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PROFESSOR: OK.

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I guess we'll get started.

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So last time we were talking
about the auditory midbrain,

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where the big structure is
the inferior colliculus.

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And we talked about
its inputs coming

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from the superior
olivary nuclei,

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like the lateral
superior olive, which

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has neuron sensitive to
enter oral level differences,

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and another input
being the MSO, where

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the neurons insensitive
to binaural stimuli

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with interaural
time differences.

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And those inputs converge
on the inferior colliculus.

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And in today's lecture,
we have a little slide

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of the inferior colliculus.

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And the big part of the inferior
colliculus, diagrammed here

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is this central
nucleus, the ICC.

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And that structure
has been well studied,

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part because it's the big part.

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It's easy to record from,
it's deep in the brain.

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It has a strong
tonotopic organization.

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We talked last time about
neurons there having

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time intensity trading because
they get in some cases, input

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from both LSO and MSO.

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We talked about coding for
stimulating head precedence

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like effects in the
inferior colliculus,

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and we talked a little bit about
sound localization in there

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in the mammal, at
least for the parts

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of the inferior colliculus
that had been studied,

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there being no really good or
obvious map of sound location

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to place in the colliculus,
and we also talked about some

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of the other edge
regions of the colliculus

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like the external nucleus
of the colliculus that

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has been explored very
nicely in the bar now.

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And we talked about
its projections

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up to the optic tectum,
or the tectum in the bar

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now, which is the analog
of the superior colliculus

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in the mammal.

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And there's this
beautiful mapping

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of auditory space
in the barn owl

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at that position in the brain.

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Now, such mappings are
not found in general

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in the auditory
system of mammals,

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with the one exception
being in the deep layers

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of the superior colliculus.

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There are neurons that are
responsive to auditory,

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as well as visual stimuli.

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Of course, we think of
the superior colliculus

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as being a visual nucleus.

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And in those deeper
layers, there

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is a mapping of
auditory space that's

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in line with the mapping
for visual space there.

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So it's as if a mapping of space
can be created in the mammal,

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but it just doesn't
appear, at least

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in the main nuclei of
the auditory pathway.

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The superior colliculus is
really not an auditory nucleus.

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OK.

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So any questions from last time?

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So today, we're going to
be talking about mainly

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the auditory cortex
and how it has

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a number of fields
in the cortex.

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Usually we talk about
fields rather than nuclei,

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and these fields
are tonotopically

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organized-- at least,
several of them are.

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And some of them
aren't, but we'll

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be emphasizing the
tonotopic ones.

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There are some very
interesting experiments

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where investigators have
explored how changes in hearing

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can affect the tonotopic
mappings in these fields

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so that they can be plastic.

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They can be molded or shaped
depending on experience.

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So we'll talk about
that plasticity.

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Because there are many
fields, the obvious question

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is, well, what does one field
do in your sense of hearing,

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and what does another field do.

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And we're generally not able
to answer those questions.

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I like to think that there
are Nobel Prizes waiting

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to be earned in this area as
that function is worked out

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for each of the fields.

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But it's clear that there's a
big role of one field, which

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we call A1, in
sound localization.

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And we'll review that
line of investigation.

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That if A1 is lost, an
experimental animal's ability

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to localize sounds
is completely gone.

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OK?

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So we'll talk about
the evidence, how

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we test animals for
sound localization.

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Then we'll talk about where
A1 is in the human auditory

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cortex.

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And we'll talk finally about
some very interesting imaging

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studies that have shown that
there is a center that lights

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up in imaging studies
when you present

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sounds with salient pitch.

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That is, very strong
sensations of pitch,

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and it's an area near A1,
but a little bit beyond it.

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So we'll talk about
those imaging studies.

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And that relates to
the paper that we

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have for assigned reading
for today's lecture.

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So that's the roadmap for today.

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So the first slide is a
very complicated slide

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that as I said, has the
inferior colliculus on it.

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And in the second row, has
the auditory thalamus on it.

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So the auditory thalamus
is the medial geniculate.

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And I'm not going
to say very much

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about the medial geniculate.

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Probably Peter Schiller
talked a lot more

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about the lateral geniculate in
the visual part of the course.

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I want to just say that
there is a large part

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of the medial geniculate called
the ventral division, indicated

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here.

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There's a couple
little symbols that

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say v. That stands
for ventral division.

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And there is a large part
of the medial geniculate

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that is tonotopically organized.

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And so it receives
a lot of input

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from the central nucleus of the
colliculus, which is tonotopic.

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It is tonotopic.

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And it, in turn, projects
2 auditory cortical fields

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that are listed up
there, which we'll

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go over in detail
in just a minute.

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And all of those
listed cortical fields,

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with the exception of the
one that says t, all of those

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are tonotopically organized.

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So to some people
than, there is a part

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of this auditory pathway
at these higher levels

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that's called the
tonotopic system.

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And that has a
bulk of the nuclei.

00:07:42.660 --> 00:07:44.090
There are some other systems.

00:07:45.120 --> 00:07:48.950
And at least in
this author's idea,

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they're labeled as diffuse
and multisensory systems.

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We're not going to
talk much about them.

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But they start out in other
parts of the colliculus,

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like the dorsal part
of the colliculus,

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and the external nucleus
of the colliculus.

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And they pass through other
divisions of the thalamus.

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And they either go to other
auditory cortical fields,

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like A2 here, or they
project diffusely

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to a whole bunch of
places in auditory cortex.

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So we're not going to emphasize
them very much at all.

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Just stick with the
tonotopic system for now.

00:08:29.580 --> 00:08:33.620
So in the auditory
cortex, there's

00:08:33.620 --> 00:08:37.799
been a lot of research done
on the cortex of the cat.

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Cat has been a standard
model for auditory cortex

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work since the beginning,
since the '60s.

00:08:46.230 --> 00:08:48.815
And so the fields are very
well known in the cat.

00:08:49.840 --> 00:08:54.000
And they're indicated in
the colored shading here.

00:08:54.000 --> 00:08:56.940
And this is showing
you the cat's brain

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from looking at its left side.

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So you see that the colored
areas, the auditory areas,

00:09:05.070 --> 00:09:08.520
are in the part of
the brain called

00:09:08.520 --> 00:09:13.530
the temporal cortex,
the side of the cortex.

00:09:13.530 --> 00:09:19.820
So way up here would be the
frontal part of the cortex,

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the frontal lobes here.

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Way back here, you're familiar
with the occipital cortex,

00:09:25.130 --> 00:09:26.655
which would be the visual areas.

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And these areas are on the side,
our so-called temporal cortex.

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Those are the auditory areas.

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And the cat is a nice
model for cortex.

00:09:38.350 --> 00:09:41.900
Because much of the big
auditory cortical field,

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A1 here, is on the surface.

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It's on a big gyrus
that's accessible.

00:09:52.530 --> 00:09:55.020
You can get to it, you
can record from it.

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You can make lesions in it.

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A little bit of A1 goes
down into a sulcus.

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And those sulci are
labeled by the lines.

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This one is labeled ps, the
posterior ectosylvian sulcus.

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And this is the cortex with
the cortex map pulled apart.

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So you can see the parts
of the cortex that's

00:10:19.150 --> 00:10:21.820
down in the sulcus.

00:10:21.820 --> 00:10:24.330
And those are the
dark pink here.

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And in the front part, rostral
part of the auditory cortex,

00:10:28.450 --> 00:10:31.970
there's another anterior
ectosylvian sulcus.

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And that's shown by
the dark pink here.

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So much of A1 is on the
surface, but a little bit of it

00:10:37.700 --> 00:10:40.075
dives down into a sulcus.

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Now, when you go with
microelectrodes and record

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from the auditory cortex,
you take off the skull,

00:10:53.350 --> 00:10:55.910
you take off the dura,
and you see the cortex.

00:10:55.910 --> 00:10:57.410
And you can take
your microelectrode

00:10:57.410 --> 00:11:00.170
and go right into the cortex.

00:11:00.170 --> 00:11:02.940
And of course, the
cortex has layers.

00:11:02.940 --> 00:11:06.590
So you'd be going, starting
in layer 1, and going down.

00:11:06.590 --> 00:11:09.140
How many layers are
there in cortex?

00:11:09.140 --> 00:11:10.700
There's 6, right?

00:11:12.120 --> 00:11:12.830
OK.

00:11:12.830 --> 00:11:16.030
And you find that if you go
down through all those layers

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and make recordings in
the different layers,

00:11:18.500 --> 00:11:21.790
all of the neurons in
one cortical penetration

00:11:21.790 --> 00:11:23.574
with your electrode
have the same CF.

00:11:24.936 --> 00:11:29.120
So of course, we want to measure
the characteristic frequency

00:11:29.120 --> 00:11:31.905
from the tuning curve, just
like we do in other places.

00:11:33.410 --> 00:11:37.150
And if you do that,
in these recordings

00:11:37.150 --> 00:11:39.045
you find that they
all have the same CF.

00:11:39.045 --> 00:11:44.090
And that's like going down
through a cortical column.

00:11:45.700 --> 00:11:51.510
So columnar organization is
very important in cortex.

00:11:56.960 --> 00:12:00.685
And if we draw it from the
side, this would be the surface.

00:12:02.860 --> 00:12:06.080
And you'd have these 6
layers usually labeled

00:12:06.080 --> 00:12:07.100
by Roman numerals.

00:12:14.250 --> 00:12:18.150
And your electrode would be
coming down here and sampling

00:12:18.150 --> 00:12:21.900
from the various layers,
single neurons at a time.

00:12:21.900 --> 00:12:24.540
Of course, you'd have to
maybe record from layer 1

00:12:24.540 --> 00:12:27.590
first, then layer 2, and
then so on, and so forth.

00:12:28.940 --> 00:12:34.110
And as long as you stay
within a column of cortex,

00:12:34.110 --> 00:12:37.640
the neurons have the same
characteristic frequency.

00:12:37.640 --> 00:12:41.190
So looking at it from
the surface here then,

00:12:41.190 --> 00:12:43.210
one column would be like a dot.

00:12:43.210 --> 00:12:44.950
You'd be looking
down at the very top

00:12:44.950 --> 00:12:49.190
of the column from the capital
down to the base of the column,

00:12:49.190 --> 00:12:50.890
if it were an
architectural column.

00:12:52.420 --> 00:12:56.600
When you do that, you
can make a CF mapping

00:12:56.600 --> 00:12:59.250
for these tonotopic fields.

00:12:59.250 --> 00:13:03.720
And you find that if you're
way over here, rostral in A1,

00:13:03.720 --> 00:13:06.455
you get very high CFs.

00:13:06.455 --> 00:13:11.170
And so high CFs for a cat would
be like 40 kilohertz, maybe

00:13:11.170 --> 00:13:13.220
even 50 kilohertz.

00:13:13.220 --> 00:13:17.270
An octave beyond the upper
limit of human hearing.

00:13:17.270 --> 00:13:21.210
But if you move your
electrode, more caudally,

00:13:21.210 --> 00:13:24.020
the CFs get lower,
and lower, and lower

00:13:24.020 --> 00:13:26.790
until you reach the
posterior edge of A1.

00:13:27.870 --> 00:13:29.860
And this little
word, "low" means,

00:13:29.860 --> 00:13:35.130
that's where the lowest
CFs in A1 would be found.

00:13:35.130 --> 00:13:40.805
And the low CFs would be like
0.1 kilohertz, 100 Hertz.

00:13:43.150 --> 00:13:48.010
If you went perpendicular to
that so-called tonotopic axis,

00:13:48.010 --> 00:13:52.301
you can have recordings that go
one here, one there, one there,

00:13:52.301 --> 00:13:52.800
one there.

00:13:52.800 --> 00:13:55.270
If you're moving up
from ventral to dorsal,

00:13:55.270 --> 00:13:57.610
then you find they
all have the same CFs.

00:13:57.610 --> 00:13:59.153
So that's an iso CF.

00:14:00.452 --> 00:14:02.170
Lamina, if you will.

00:14:03.570 --> 00:14:05.000
And it starts right here.

00:14:05.000 --> 00:14:06.930
This line right here
is an iso CF lamina.

00:14:06.930 --> 00:14:08.200
This would be the highest CFs.

00:14:10.400 --> 00:14:12.020
And then as you go
caudally the CFs

00:14:12.020 --> 00:14:13.353
get lower, and lower, and lower.

00:14:14.900 --> 00:14:19.280
Then, when you keep moving
your electrode, more and more

00:14:19.280 --> 00:14:23.510
caudally, you find further CFs.

00:14:23.510 --> 00:14:26.870
And then the
progression changes.

00:14:26.870 --> 00:14:29.575
The CFs start to become
higher, and higher, and higher.

00:14:31.720 --> 00:14:35.410
That's the signal that you've
entered another auditory

00:14:35.410 --> 00:14:38.840
cortical field right behind A1.

00:14:40.410 --> 00:14:42.616
And it gets its name
from being behind it,

00:14:42.616 --> 00:14:44.910
behind an anatomical
terminology is posterior.

00:14:46.100 --> 00:14:49.590
So this field is p,
or sometimes called

00:14:49.590 --> 00:14:52.620
PAF, posterior auditory field.

00:14:53.770 --> 00:14:57.270
And if you keep going,
more and more caudally.

00:14:57.270 --> 00:14:59.840
In this case, the
thing takes a turn.

00:14:59.840 --> 00:15:02.830
So you go, caudally and
ventrally, the CFs then

00:15:02.830 --> 00:15:09.880
start to get higher, until
you approach the boundary of p

00:15:09.880 --> 00:15:13.470
with the next auditory
cortical field, which is VP.

00:15:13.470 --> 00:15:17.580
Ventral posterior
auditory field.

00:15:17.580 --> 00:15:21.070
Then the CFs go
from high to low.

00:15:23.410 --> 00:15:29.290
Same thing happens where A1
meets the anterior auditory

00:15:29.290 --> 00:15:31.780
field, indicated by a here.

00:15:31.780 --> 00:15:36.013
Those two fields share a high
frequency, high CF boundary.

00:15:37.190 --> 00:15:38.704
And then, as you
go more rostral,

00:15:38.704 --> 00:15:40.370
the CFs get lower,
and lower, and lower.

00:15:41.800 --> 00:15:46.600
Sometimes this organization,
at the edges of the fields,

00:15:46.600 --> 00:16:02.780
is called, mirror image
tonotopy in the auditory system.

00:16:02.780 --> 00:16:04.660
And where else have
you guys seen this?

00:16:09.340 --> 00:16:12.410
Did you go over this in the
vision part of the course

00:16:12.410 --> 00:16:17.220
where you have the mapping
of the retina on V1

00:16:17.220 --> 00:16:19.150
in the occipital cortex, right?

00:16:19.150 --> 00:16:20.935
And it has a retina
topic mapping.

00:16:22.570 --> 00:16:25.890
And that has some image where
the nasal part of the retina

00:16:25.890 --> 00:16:29.560
is over here, and the temporal
part of the retina's over here.

00:16:29.560 --> 00:16:34.580
And where V1 abuts V2, you also
have a retina topic mapping.

00:16:34.580 --> 00:16:37.975
But it's a mirror
image reversal of V1.

00:16:39.600 --> 00:16:41.190
So you should have
gone over that

00:16:41.190 --> 00:16:42.565
in the visual part
of the course.

00:16:44.030 --> 00:16:50.590
You find such mirror image flips
in the somatosensory cortex.

00:16:51.690 --> 00:16:53.950
In the somatosensory
cortex, there's

00:16:53.950 --> 00:16:57.260
a mapping of the body surface.

00:16:57.260 --> 00:16:59.470
If you touch here
on the body surface,

00:16:59.470 --> 00:17:02.524
a certain part of the
somatosensory cortex responds.

00:17:02.524 --> 00:17:04.524
If you touch up here, a
different part responds.

00:17:04.524 --> 00:17:08.650
And there's a mapping
of the body surface

00:17:08.650 --> 00:17:10.770
onto the surface of the cortex.

00:17:10.770 --> 00:17:15.310
And where S1 meets S2,
there's also a mapping.

00:17:15.310 --> 00:17:16.465
But it's a mirror image.

00:17:17.619 --> 00:17:18.119
OK.

00:17:18.119 --> 00:17:20.569
So this is not a
surprise in terms

00:17:20.569 --> 00:17:23.990
of general cortical
organization.

00:17:23.990 --> 00:17:28.950
And it's also not a surprise
in the visual periphery.

00:17:28.950 --> 00:17:31.030
You have the retina
topic mapping.

00:17:31.030 --> 00:17:33.216
In the auditory periphery,
you have the CF mapping.

00:17:34.320 --> 00:17:36.925
And you have this nice CF
mapping along the cortex.

00:17:40.070 --> 00:17:40.570
OK.

00:17:40.570 --> 00:17:44.520
And in the cat, you have
these four tonotopically

00:17:44.520 --> 00:17:46.520
organized system fields.

00:17:46.520 --> 00:17:53.080
And you have several
fields; A2, DPV, and T,

00:17:53.080 --> 00:17:56.686
where the tonotopy is either
nonexistent, or much less

00:17:56.686 --> 00:17:57.185
obvious.

00:17:58.860 --> 00:18:01.920
And there are some
challenges here

00:18:01.920 --> 00:18:06.380
to exploring responses
in these other areas.

00:18:06.380 --> 00:18:18.305
For example, tuning curves in
A2 can sometimes look like this.

00:18:20.520 --> 00:18:25.145
And it's very difficult
then, to assign a CF

00:18:25.145 --> 00:18:28.880
to such a broad bowl
shaped tuning curve.

00:18:28.880 --> 00:18:30.790
You could do it, if you
really were pressed.

00:18:30.790 --> 00:18:33.990
But there's not much difference
between that frequency

00:18:33.990 --> 00:18:34.920
and that frequency.

00:18:34.920 --> 00:18:39.170
So this could be an
octave or more difference.

00:18:39.170 --> 00:18:42.740
And so it's hard to
assign a CF to some

00:18:42.740 --> 00:18:45.330
of the neurons in
these other fields.

00:18:45.330 --> 00:18:47.480
That's not true in A1.

00:18:47.480 --> 00:18:50.170
In the tonotopically
organize fields in general,

00:18:50.170 --> 00:18:53.110
there's very precise,
sharp frequency tuning.

00:18:55.571 --> 00:18:56.070
OK.

00:18:56.070 --> 00:18:59.030
So the tuning curves,
there's a little table here.

00:18:59.030 --> 00:19:04.080
They're usually sharp in these
tonotopically organized fields.

00:19:04.080 --> 00:19:05.940
Yes, there's tonotopic
organization.

00:19:05.940 --> 00:19:06.865
The latency is short.

00:19:09.430 --> 00:19:11.940
The response is brisk
or robust compared

00:19:11.940 --> 00:19:15.420
to response that might be
called poor or insecure.

00:19:15.420 --> 00:19:20.080
That just simply means, every
time you turn on a sound,

00:19:20.080 --> 00:19:22.340
and people remember,
typically tend

00:19:22.340 --> 00:19:24.590
to measure histograms
in response

00:19:24.590 --> 00:19:28.900
to hundreds of sound bursts
every time there's a response.

00:19:28.900 --> 00:19:30.550
But here, there
might be a response

00:19:30.550 --> 00:19:32.740
to the first tone
burst in a train.

00:19:32.740 --> 00:19:35.240
And then the neuron might shut
down and not respond anymore.

00:19:36.570 --> 00:19:41.290
So these diffuse areas
are hard to investigate.

00:19:44.110 --> 00:19:47.290
Most of these cortex
recordings I'm talking about

00:19:47.290 --> 00:19:49.940
have been done in
anesthetized animals.

00:19:49.940 --> 00:19:51.800
And so there's
always a question of,

00:19:51.800 --> 00:19:56.080
how much has anesthesia
changed the response patterns?

00:19:56.080 --> 00:19:59.190
Of course, anesthesia
has a big effect

00:19:59.190 --> 00:20:01.300
on these higher levels
of the nervous system.

00:20:01.300 --> 00:20:05.190
So it's not always clear
how much of these properties

00:20:05.190 --> 00:20:08.015
or change in these properties
has been due to anesthesia.

00:20:11.510 --> 00:20:14.640
So back to the
somatosensory cortex.

00:20:16.620 --> 00:20:20.180
Here's a mapping of the
somatosensory cortex.

00:20:20.180 --> 00:20:23.520
And this is the
surface of the body map

00:20:23.520 --> 00:20:26.120
onto the surface of
the cortex that I

00:20:26.120 --> 00:20:28.030
was referring to earlier.

00:20:29.090 --> 00:20:33.670
So if you stimulate
the surface of the body

00:20:33.670 --> 00:20:35.710
over here, the tips
of the toes, you

00:20:35.710 --> 00:20:38.330
get a response here in
the somatosensory cortex.

00:20:39.460 --> 00:20:42.200
If you stimulate the
fingers, you get a response

00:20:42.200 --> 00:20:45.480
here in the
somatosensory cortex.

00:20:45.480 --> 00:20:49.040
You stimulate the facial region,
you get a response over here.

00:20:50.320 --> 00:20:55.090
And this distorted
mapping or caricature

00:20:55.090 --> 00:20:58.620
of the body's surface,
sometimes called a homunculus.

00:20:58.620 --> 00:21:02.460
And it shows you
that a lot of cortex

00:21:02.460 --> 00:21:05.940
is devoted to certain
important parts of your body,

00:21:05.940 --> 00:21:06.665
like the face.

00:21:07.720 --> 00:21:11.710
And less important parts,
like the trunk of your body,

00:21:11.710 --> 00:21:16.240
receives much smaller
representation in the cortex.

00:21:17.710 --> 00:21:19.760
In the auditory
cortex, if you draw

00:21:19.760 --> 00:21:24.380
the mapping-- so
here's a mapping of A1.

00:21:25.970 --> 00:21:28.505
In this case, it's from
the guinea pig cortex.

00:21:29.900 --> 00:21:32.230
And in this case, the
mapping is plotted

00:21:32.230 --> 00:21:36.620
with the CF on the
y-axis, and the distance

00:21:36.620 --> 00:21:40.640
along the cortex on the x-axis.

00:21:40.640 --> 00:21:42.300
And these are the data.

00:21:42.300 --> 00:21:44.830
Each dot indicates
a recording site

00:21:44.830 --> 00:21:47.470
from a single column
in the cortex.

00:21:47.470 --> 00:21:48.970
And if you could
read these numbers,

00:21:48.970 --> 00:21:50.255
they would indicate the CFs.

00:21:51.830 --> 00:21:55.952
And these lines are
the ISO CF contours.

00:21:57.550 --> 00:22:02.160
And this CF axis is plotted
along this distance here.

00:22:02.160 --> 00:22:05.230
So this distance
is going like this,

00:22:05.230 --> 00:22:07.290
and this distance is
going along like this.

00:22:07.290 --> 00:22:10.923
And there's a very nice,
almost linear relationship.

00:22:12.530 --> 00:22:15.450
And it shows you
something quite different

00:22:15.450 --> 00:22:17.900
from the somatosensory
mapping, which

00:22:17.900 --> 00:22:20.786
is that there aren't any
really important frequencies.

00:22:22.630 --> 00:22:26.130
They all have about the same
representation in the cortex.

00:22:26.130 --> 00:22:30.170
It's a pretty boring,
straight line, if you will.

00:22:30.170 --> 00:22:34.460
It's not as interesting
as the homunculus

00:22:34.460 --> 00:22:35.905
in the somatosensory cortex.

00:22:37.110 --> 00:22:39.300
So this is true in
the general mammal.

00:22:40.380 --> 00:22:44.270
Next time, when we talk about
the auditory cortex in the echo

00:22:44.270 --> 00:22:48.210
locating bat, we'll have
quite a different finding.

00:22:48.210 --> 00:22:50.480
There are some very
important frequencies

00:22:50.480 --> 00:22:54.780
in certain types of bats that
relate to the echo locating

00:22:54.780 --> 00:22:57.730
signal that they
emit, and the echo

00:22:57.730 --> 00:23:00.900
that comes back to them so
that they can find targets,

00:23:00.900 --> 00:23:01.700
even in the dark.

00:23:02.910 --> 00:23:06.880
But most of general mammals
do not echolocate, of course.

00:23:06.880 --> 00:23:10.900
And so their mapping
of the sensory cortex

00:23:10.900 --> 00:23:15.180
is pretty linear and
boring, if you will.

00:23:15.180 --> 00:23:19.460
So today's reading
comes from what

00:23:19.460 --> 00:23:23.110
motivates the next
experiment that I'll show.

00:23:23.110 --> 00:23:24.900
For a long time,
these mappings were

00:23:24.900 --> 00:23:29.230
thought to be laid down at
birth and not changeable.

00:23:29.230 --> 00:23:30.865
So they were just immutable.

00:23:31.970 --> 00:23:34.290
But some very
interesting experiments

00:23:34.290 --> 00:23:39.260
by Dexter Irvine and Don
Robertson in the 1980s

00:23:39.260 --> 00:23:41.320
showed that was not true.

00:23:41.320 --> 00:23:44.770
And they were not the
pioneers in showing

00:23:44.770 --> 00:23:47.745
that cortex can change as
a result of experiment.

00:23:48.960 --> 00:23:52.240
Rather, some people who
were working, especially

00:23:52.240 --> 00:23:55.550
in the somatosensory
cortex, were the first.

00:23:55.550 --> 00:23:59.770
And so I didn't have
a reading for today.

00:23:59.770 --> 00:24:03.650
So right before I came over, I
pulled up the Wikipedia entry

00:24:03.650 --> 00:24:05.340
on the Silver Spring monkeys.

00:24:05.340 --> 00:24:08.320
So has anybody heard of
the Silver Spring monkeys?

00:24:09.890 --> 00:24:15.850
So Silver Spring monkeys were
in the news in the 1980s.

00:24:15.850 --> 00:24:17.810
They got their name
from the Institute

00:24:17.810 --> 00:24:22.180
of Behavioral Research in Silver
Springs, Maryland-- Silver

00:24:22.180 --> 00:24:24.230
Spring, Maryland.

00:24:24.230 --> 00:24:28.890
And from 1981 to
1991, they became

00:24:28.890 --> 00:24:33.560
what one writer called, the most
famous lab animals in history,

00:24:33.560 --> 00:24:37.930
as a result of battle between
animal researchers, animal

00:24:37.930 --> 00:24:40.650
advocates, politicians,
and courts.

00:24:40.650 --> 00:24:45.340
So there was a researcher
whose name was Edward Taub.

00:24:45.340 --> 00:24:49.720
And he was experimenting on the
somatosensory sensory cortex.

00:24:49.720 --> 00:24:51.730
And he was taking
the monkeys, and he

00:24:51.730 --> 00:24:54.950
was denervating
the sensory input

00:24:54.950 --> 00:24:56.860
from certain parts
of their limbs.

00:24:56.860 --> 00:25:01.110
So for example, he would cut the
nerves that carried information

00:25:01.110 --> 00:25:04.330
from the middle
finger of the monkeys.

00:25:04.330 --> 00:25:09.210
And he was studying to see
if the somatosensory cortex

00:25:09.210 --> 00:25:12.520
remapped, and he was
finding small effects.

00:25:12.520 --> 00:25:19.300
But in May, 1981, Alex Pacheco,
from the animal rights group

00:25:19.300 --> 00:25:22.250
PETA, began working
undercover in his lab,

00:25:22.250 --> 00:25:26.816
alerted the police to what PETA
viewed as unacceptable living

00:25:26.816 --> 00:25:27.940
conditions for the monkeys.

00:25:29.180 --> 00:25:31.650
And there was a long battle.

00:25:31.650 --> 00:25:35.060
Initially, the researcher was
convicted of animal cruelty,

00:25:35.060 --> 00:25:37.610
and these charges were
subsequently overturned.

00:25:41.410 --> 00:25:44.740
But anyway, the monkeys
were held in limbo

00:25:44.740 --> 00:25:48.770
for in some cases, many
years because his research

00:25:48.770 --> 00:25:49.530
was put on hold.

00:25:50.540 --> 00:25:53.030
During the subsequent
experiments

00:25:53.030 --> 00:25:55.900
on the monkeys after the
court battles were all done,

00:25:55.900 --> 00:25:59.710
it was discovered that
significant cortical remapping

00:25:59.710 --> 00:26:00.350
had occurred.

00:26:02.110 --> 00:26:04.210
This is evidence of
the brain's plasticity,

00:26:04.210 --> 00:26:06.980
and it helped to overturn the
widely held view that the old

00:26:06.980 --> 00:26:10.250
adult brain cannot reorganize
itself in response to its

00:26:10.250 --> 00:26:11.480
environment.

00:26:11.480 --> 00:26:16.090
So the analogous experiments
in the auditory system

00:26:16.090 --> 00:26:17.980
have been done in small animals.

00:26:17.980 --> 00:26:22.930
And maybe it's a result
of much decline and use

00:26:22.930 --> 00:26:24.525
of primates in research.

00:26:24.525 --> 00:26:27.420
There was hardly
any auditory work

00:26:27.420 --> 00:26:29.470
done on primates these days.

00:26:29.470 --> 00:26:32.505
This reorganization work
is done in the guinea pigs.

00:26:33.850 --> 00:26:35.805
And the experiments
are done like this.

00:26:38.320 --> 00:26:43.530
There's a peripheral lesion
made in the cochlear.

00:26:43.530 --> 00:26:47.560
In the Guinea pig
cochlear, it's very easy

00:26:47.560 --> 00:26:50.250
to make a little hole
in the middle layer,

00:26:50.250 --> 00:26:51.500
and look down on the cochlear.

00:26:51.500 --> 00:26:53.405
And the cochlear's
a bony structure.

00:26:55.260 --> 00:26:58.950
The most accessible part is
the basal turn of the cochlear.

00:26:58.950 --> 00:27:01.260
And you can go right
through the round window

00:27:01.260 --> 00:27:04.435
and see the basilar
membrane, and the hair cells.

00:27:05.610 --> 00:27:09.820
And you can make a
little tiny pinpoint

00:27:09.820 --> 00:27:15.500
opening in the organ of
corti with a fine metal pick,

00:27:15.500 --> 00:27:17.880
and create a
substantial hearing loss

00:27:17.880 --> 00:27:19.935
in one little place
of the cochlear.

00:27:21.150 --> 00:27:25.380
So here is indicated a
graph of the compound action

00:27:25.380 --> 00:27:27.080
potential threshold.

00:27:27.080 --> 00:27:29.820
This is a response from
the auditory nerve.

00:27:29.820 --> 00:27:32.090
Action potential,
obviously, is an impulse

00:27:32.090 --> 00:27:34.030
from single auditory
nerve fibers.

00:27:34.030 --> 00:27:37.960
Compound means it's a
recording from many, many,

00:27:37.960 --> 00:27:41.730
if not all of the
auditory nerve in response

00:27:41.730 --> 00:27:46.190
to a tone burst of the
different frequencies.

00:27:46.190 --> 00:27:48.560
And if you make a small
lesion at the basal turn,

00:27:48.560 --> 00:27:50.950
remember the frequency
organization of the cochlear

00:27:50.950 --> 00:27:55.860
is such that the basal turn
processes, high frequencies.

00:27:57.190 --> 00:28:01.400
And so instead of the normal
curve in the lesion animal,

00:28:01.400 --> 00:28:05.710
you have a big increase in
threshold, maybe 60, or 70,

00:28:05.710 --> 00:28:08.820
or 80 dB in the lesion case.

00:28:10.280 --> 00:28:13.760
And that lesion goes
from about 10 kilohertz

00:28:13.760 --> 00:28:15.075
to about 20 kilohertz.

00:28:16.460 --> 00:28:19.240
And in other parts
of the cochlear,

00:28:19.240 --> 00:28:21.090
the hearing is normal.

00:28:21.090 --> 00:28:23.315
So this is a peripheral
hearing loss.

00:28:26.020 --> 00:28:29.720
And now, we're going to
then look in the cortex

00:28:29.720 --> 00:28:32.714
and see if the tonotopy
of the auditory cortex

00:28:32.714 --> 00:28:33.755
is the same or different.

00:28:33.755 --> 00:28:35.740
And obviously, my
big build up here,

00:28:35.740 --> 00:28:38.850
that there's plasticity
of tonotopy, is found.

00:28:39.900 --> 00:28:43.880
This is the normal
mapping that we first saw.

00:28:43.880 --> 00:28:47.460
This is the mapping in
the lesioned animal.

00:28:47.460 --> 00:28:50.610
And in this case, it's a mapping
where each of these dots,

00:28:50.610 --> 00:28:52.590
of course, is a recording site.

00:28:52.590 --> 00:28:54.175
These are very high CFs.

00:28:55.720 --> 00:28:58.390
You march along here, and
the CF gets a little lower.

00:28:59.590 --> 00:29:04.850
But there's a big region
of about 20 kilohertz--

00:29:04.850 --> 00:29:08.230
big, long distance in the
cortex-- when all you get

00:29:08.230 --> 00:29:09.915
is CFs of 20 kilohertz.

00:29:11.900 --> 00:29:14.535
Notice that that is right
at the edge of the lesion.

00:29:17.160 --> 00:29:21.120
In the lesion, between
20 and 10 kilohertz,

00:29:21.120 --> 00:29:23.050
you don't get any response.

00:29:23.050 --> 00:29:25.000
Well, there's a huge
hearing loss there.

00:29:25.000 --> 00:29:27.670
It's no surprise that there's no
response to those frequencies.

00:29:28.790 --> 00:29:32.440
The auditory periphery is
not sending you any messages,

00:29:32.440 --> 00:29:35.260
or sending you very few messages
about those frequencies.

00:29:36.740 --> 00:29:39.385
Then you jump a little
bit in distance.

00:29:40.680 --> 00:29:45.030
And the CF jumped from
20 down to 10 kilohertz.

00:29:45.030 --> 00:29:47.370
And there's a long
region of cortex

00:29:47.370 --> 00:29:49.400
at which the CFs are
all 10 kilohertz.

00:29:51.050 --> 00:29:53.730
And notice that 10 kilohertz
is a very important frequency

00:29:53.730 --> 00:29:56.130
in the audiogram of this
animal, and that it's

00:29:56.130 --> 00:29:58.790
right at the edge, the low
frequency edge of the hearing

00:29:58.790 --> 00:29:59.290
loss.

00:30:00.840 --> 00:30:02.940
After that extensive
region then, you

00:30:02.940 --> 00:30:07.400
pick up your normal
tonotopy of auditory cortex.

00:30:08.760 --> 00:30:12.700
So this is clearly a
massive reorganization

00:30:12.700 --> 00:30:20.190
compared to the normal
of this lesioned animal's

00:30:20.190 --> 00:30:21.110
cortical mapping.

00:30:21.110 --> 00:30:23.250
So couple comments about this.

00:30:25.100 --> 00:30:31.520
If you do the mapping
right after the lesion,

00:30:31.520 --> 00:30:33.875
this reorganization
is not found.

00:30:35.990 --> 00:30:37.135
So it takes some time.

00:30:41.350 --> 00:30:42.970
In the case of the
auditory system,

00:30:42.970 --> 00:30:49.026
it takes more than three weeks
to see the reorganization.

00:30:58.960 --> 00:31:00.886
What's the mechanism
for this reorganization?

00:31:09.240 --> 00:31:17.510
Well, we have input coming
up to here from the thalamus,

00:31:17.510 --> 00:31:19.580
where the inputs
from the 20 kilohertz

00:31:19.580 --> 00:31:22.535
place of the thalamus,
did they come up here?

00:31:23.950 --> 00:31:28.650
And did they grow into a
large part of the cortex

00:31:28.650 --> 00:31:31.250
where they weren't
present before?

00:31:31.250 --> 00:31:35.640
And did they do that growth
because that part of the cortex

00:31:35.640 --> 00:31:38.790
had gone silent because
of the hearing loss?

00:31:38.790 --> 00:31:45.780
So one mechanism
could be growth,

00:31:45.780 --> 00:31:48.065
if you will, sideways
growth of axons.

00:31:52.870 --> 00:31:56.580
Another mechanism
could be the inputs

00:31:56.580 --> 00:31:58.270
from the thalamus
are coming up here.

00:31:58.270 --> 00:32:00.830
And even in the normal
case, they don't just

00:32:00.830 --> 00:32:03.890
go to one place, but they have
all sorts of side branches.

00:32:05.160 --> 00:32:09.470
And these side branches in
the normal case are inhibited,

00:32:09.470 --> 00:32:12.550
or they're not
strong to begin with.

00:32:12.550 --> 00:32:15.290
Because there's a lot of
other stuff coming in here,

00:32:15.290 --> 00:32:17.640
and the other stuff is
saying, you guys be quiet.

00:32:17.640 --> 00:32:18.650
I'm the main input.

00:32:19.940 --> 00:32:22.010
And maybe after
the hearing loss,

00:32:22.010 --> 00:32:23.440
that other stuff is silenced.

00:32:24.800 --> 00:32:29.050
And these previously weak
inputs become stronger.

00:32:29.050 --> 00:32:31.700
So you could say then
that another mechanism

00:32:31.700 --> 00:32:47.210
is strengthening of
preexisting inputs

00:32:47.210 --> 00:32:50.930
that are weak before
the perturbation.

00:32:50.930 --> 00:32:52.810
And I wrote mechanism, ?

00:32:52.810 --> 00:32:55.900
because we don't know
what the mechanism is.

00:32:55.900 --> 00:32:57.160
And it may be both.

00:32:57.160 --> 00:32:58.655
They're not mutually exclusive.

00:33:01.770 --> 00:33:04.390
And we're thinking here, cortex.

00:33:04.390 --> 00:33:05.800
This is a lecture on the cortex.

00:33:07.270 --> 00:33:13.973
But I should bring up, where is
the locus of this plasticity?

00:33:17.110 --> 00:33:21.280
So in the auditory system, we
have a rich array of nuclei.

00:33:21.280 --> 00:33:24.950
We have the cochlear nucleus,
we have the superior olivary

00:33:24.950 --> 00:33:28.053
complex, we have the
inferior colliculus.

00:33:29.560 --> 00:33:32.920
We've just learned a little
about the auditory thalamus.

00:33:32.920 --> 00:33:37.730
Well, could one of
those lower level nuclei

00:33:37.730 --> 00:33:41.610
have reorganized, and
then just passively spit

00:33:41.610 --> 00:33:44.290
their reorganized
input up to the cortex?

00:33:44.290 --> 00:33:47.490
And the answer is yes, and that
actually has been looked at.

00:33:50.100 --> 00:33:53.915
So there's no reorganization
in the cochlear nucleus.

00:33:56.640 --> 00:34:01.670
The part of the cochlear nucleus
that processes 20 kilohertz

00:34:01.670 --> 00:34:03.640
is supposed to be normal.

00:34:03.640 --> 00:34:07.940
In between 20 and 10 kilohertz,
you have a normal region.

00:34:07.940 --> 00:34:12.505
But it's completely silent in
these types of hearing loss.

00:34:13.850 --> 00:34:20.969
You have a small amount
of reorganization

00:34:20.969 --> 00:34:23.310
in the inferior colliculus.

00:34:23.310 --> 00:34:25.585
But it's not as big as
what we see in the cortex.

00:34:27.409 --> 00:34:30.650
And maybe in the
medial geniculate body,

00:34:30.650 --> 00:34:37.330
we have a larger reorganization,
but probably not quite as much

00:34:37.330 --> 00:34:38.949
as you do in the
auditory cortex.

00:34:38.949 --> 00:34:42.139
So there may be a little
bit of reorganization,

00:34:42.139 --> 00:34:48.139
an IC, a little bit in MGB,
and then further reorganization

00:34:48.139 --> 00:34:49.195
in auditory cortex.

00:34:50.320 --> 00:34:51.469
So that has been looked at.

00:34:51.469 --> 00:34:55.830
And the answer is at all
of these higher levels,

00:34:55.830 --> 00:34:57.010
there's reorganization.

00:34:57.010 --> 00:34:59.330
But there's maybe more as
you go higher in the pathway.

00:35:01.290 --> 00:35:02.070
Now, who cares?

00:35:02.070 --> 00:35:05.710
We usually don't have
hearing losses, right?

00:35:05.710 --> 00:35:08.230
Well I should remind
you that we had

00:35:08.230 --> 00:35:09.840
a big lecture on hearing loss.

00:35:09.840 --> 00:35:14.470
Then let me show you one
of the slides from it.

00:35:14.470 --> 00:35:20.760
So we had this slide under
the lecture on hearing loss.

00:35:20.760 --> 00:35:24.360
Well, I've given
it a new title now

00:35:24.360 --> 00:35:28.360
because I was thinking
about getting old this week.

00:35:29.930 --> 00:35:35.120
And the type of hearing loss
that you have when you get old

00:35:35.120 --> 00:35:36.900
is called presbycusis.

00:35:36.900 --> 00:35:39.140
Presbycusis is the
age related loss

00:35:39.140 --> 00:35:41.985
of hearing, especially
at high frequencies.

00:35:41.985 --> 00:35:44.360
And almost all of us are going
to go through presbycusis.

00:35:46.370 --> 00:35:51.680
This is a normal audiogram
or threshold of hearing curve

00:35:51.680 --> 00:35:54.810
when you're young, and this
is one when you get older.

00:35:56.130 --> 00:35:58.990
And invariably, we lose
our high frequency hearing.

00:36:01.080 --> 00:36:02.440
The causes are not known.

00:36:02.440 --> 00:36:06.340
But clearly it takes
place in the periphery,

00:36:06.340 --> 00:36:10.440
which is very similar to the
lesion study we just went over.

00:36:10.440 --> 00:36:12.850
It's a peripheral
hearing loss, what

00:36:12.850 --> 00:36:14.700
happens to your central pathway.

00:36:14.700 --> 00:36:22.940
It probably results in cortical
reorganization in the human.

00:36:22.940 --> 00:36:24.120
And again, I can't spell.

00:36:24.120 --> 00:36:25.205
There's a missing t here.

00:36:28.730 --> 00:36:31.800
So we probably all-- and
we have plenty of time.

00:36:31.800 --> 00:36:33.594
This hearing loss
doesn't happen in days.

00:36:33.594 --> 00:36:35.385
It happens over the
course of our lifetime.

00:36:36.670 --> 00:36:39.830
There's plenty of time
to reorganize the cortex.

00:36:39.830 --> 00:36:41.500
Now, let me go back
a little bit here

00:36:41.500 --> 00:36:44.720
and ask an interesting
question which

00:36:44.720 --> 00:36:48.465
has some negative answers,
and some positive answers.

00:36:49.750 --> 00:36:51.330
People have said, well, wow.

00:36:51.330 --> 00:36:53.490
This animal-- you
have a lot of cortex.

00:36:54.550 --> 00:36:59.205
Half a millimeter devoted
to CFs of 20 kilohertz.

00:36:59.205 --> 00:37:03.430
And you have a lot of cortex
devoted to CF of 10 kilohertz.

00:37:03.430 --> 00:37:07.630
Does this animal do something a
lot better at those frequencies

00:37:07.630 --> 00:37:11.000
than this normal animal
which just has a little bitty

00:37:11.000 --> 00:37:13.310
part of cortex devoted
to 20 kilohertz,

00:37:13.310 --> 00:37:15.790
and a little bit
devoted to 10 kilohertz.

00:37:15.790 --> 00:37:20.690
So it's not clear what the
answer is to that question yet.

00:37:20.690 --> 00:37:23.100
And people have
speculated in the normal--

00:37:23.100 --> 00:37:26.480
if you train a normal
person or a normal animal

00:37:26.480 --> 00:37:28.790
to do a task at 10 kilohertz.

00:37:28.790 --> 00:37:31.360
So they're listing to 10
kilohertz over and over again.

00:37:32.370 --> 00:37:35.220
It's clearly a training
effect for many tasks.

00:37:35.220 --> 00:37:36.485
You get better with training.

00:37:37.700 --> 00:37:39.860
Does that mean in
the normal case

00:37:39.860 --> 00:37:43.530
that we enlarge the 10
kilohertz part of our cortex?

00:37:43.530 --> 00:37:44.980
Well, it's not known.

00:37:44.980 --> 00:37:48.400
Does that means this
big area of 10 kilohertz

00:37:48.400 --> 00:37:52.370
and 20 kilohertz in the
lesioned animals cortex

00:37:52.370 --> 00:37:54.750
enable that animal to
do something better?

00:37:54.750 --> 00:37:56.047
That's not clear.

00:37:58.970 --> 00:38:02.200
There's evidence for both
answers to those questions.

00:38:05.950 --> 00:38:08.740
Let's move on to some
other properties that

00:38:08.740 --> 00:38:11.930
have been observed
in auditory cortex.

00:38:11.930 --> 00:38:16.490
And we've been stuck in
this mode and this course

00:38:16.490 --> 00:38:19.530
on frequency organization.

00:38:19.530 --> 00:38:23.160
It's clearly a very
strong component

00:38:23.160 --> 00:38:25.390
of central auditory nuclei.

00:38:25.390 --> 00:38:29.830
And here are some tuning curves
from auditory cortex neurons.

00:38:30.970 --> 00:38:33.370
You have the x-axis
being frequency,

00:38:33.370 --> 00:38:36.550
and the y-axis being
sound pressure level,

00:38:36.550 --> 00:38:38.900
response being inside
the tuning curve.

00:38:38.900 --> 00:38:41.500
In this case, they've
embellished the tuning curve

00:38:41.500 --> 00:38:44.100
a little bit by plotting
the biggest, best

00:38:44.100 --> 00:38:46.820
response in real black shading.

00:38:46.820 --> 00:38:49.890
And these are the
tuning curves we've

00:38:49.890 --> 00:38:52.330
been talking about in
the course all along.

00:38:52.330 --> 00:38:54.800
You might see goes
from the auditory nerve

00:38:54.800 --> 00:38:56.780
from cochlear nucleus
and lower levels.

00:38:58.560 --> 00:39:01.427
In the auditory
cortex, you see some

00:39:01.427 --> 00:39:02.760
of those kinds of tuning curves.

00:39:02.760 --> 00:39:05.070
But you also see from
different neurons,

00:39:05.070 --> 00:39:06.570
other types of tuning curves.

00:39:07.600 --> 00:39:10.700
And these are seen to a greater
extent in the auditory cortex,

00:39:10.700 --> 00:39:12.710
although you do see some,
to a certain extent,

00:39:12.710 --> 00:39:14.630
in the colliculus, and
to a certain extent,

00:39:14.630 --> 00:39:15.940
in the thalamus.

00:39:15.940 --> 00:39:19.150
So you see them in a numerically
greater extent in the cortex.

00:39:20.440 --> 00:39:23.575
And here is a tuning curve
that sure has a best frequency.

00:39:24.770 --> 00:39:27.555
But at that best frequency, if
you get it higher and higher

00:39:27.555 --> 00:39:29.880
in level, the neuron
actually stops

00:39:29.880 --> 00:39:34.380
responding at a pretty moderate,
and certainly at a high level.

00:39:35.750 --> 00:39:39.840
And if you study its response
inside the black shading,

00:39:39.840 --> 00:39:42.450
you can say, well, that
neuron has the best

00:39:42.450 --> 00:39:44.370
frequency, or
characteristic frequency.

00:39:44.370 --> 00:39:46.155
It also has a
characteristic level.

00:39:47.170 --> 00:39:51.660
It likes it a lot when the
tone frequency is 10 kilohertz,

00:39:51.660 --> 00:39:54.190
and the tone level is 40 dB.

00:39:54.190 --> 00:39:57.140
That's its maximal response.

00:39:57.140 --> 00:39:59.000
That's the one it
prefers, if you will.

00:40:00.010 --> 00:40:01.610
Here's a different one.

00:40:01.610 --> 00:40:03.970
A best level is somewhere
in the middle here.

00:40:03.970 --> 00:40:08.500
Here's a best level here in
a very narrow response area.

00:40:10.450 --> 00:40:14.460
So many of the neurons
in the auditory cortex

00:40:14.460 --> 00:40:16.620
has to have these not
only characteristic

00:40:16.620 --> 00:40:19.040
frequencies, but
also best levels.

00:40:19.040 --> 00:40:23.560
If you, at their CF,
raise the sound level,

00:40:23.560 --> 00:40:24.930
you get this type of pattern.

00:40:24.930 --> 00:40:27.720
These are rate level functions.

00:40:27.720 --> 00:40:31.480
So this is the firing rate, and
this is the tone level or tone

00:40:31.480 --> 00:40:32.579
intensity.

00:40:32.579 --> 00:40:34.120
And this is from a
number of neurons.

00:40:34.120 --> 00:40:35.650
But just concentrate
on this one.

00:40:35.650 --> 00:40:39.700
The firing rate goes up with
level, reaches a maximum,

00:40:39.700 --> 00:40:41.010
and then it declines.

00:40:41.010 --> 00:40:45.050
And at the highest level,
it doesn't respond anymore.

00:40:45.050 --> 00:40:47.520
So we don't know
what this means.

00:40:47.520 --> 00:40:51.420
It means somehow that
these neurons could

00:40:51.420 --> 00:40:56.920
tell the animal or the person,
well, the sound level is x dB.

00:40:58.630 --> 00:41:00.340
They can tell you
the sound frequency

00:41:00.340 --> 00:41:04.900
is a certain number of
kilohertz in the sound level

00:41:04.900 --> 00:41:08.490
if they're responding
maximally, is a certain SPO.

00:41:10.220 --> 00:41:12.780
It's clearly very different.

00:41:12.780 --> 00:41:18.820
Now, I brought that
up because people

00:41:18.820 --> 00:41:23.180
have looked at that
in terms of coding

00:41:23.180 --> 00:41:28.686
for preferred areas of space
where the neuron's response is

00:41:28.686 --> 00:41:29.185
maximum.

00:41:30.630 --> 00:41:40.000
And these are some data from
Clarey et al on azimuth level

00:41:40.000 --> 00:41:42.220
response areas for
cortical neurons.

00:41:42.220 --> 00:41:43.515
So what does that mean?

00:41:43.515 --> 00:41:46.990
Well, they're recording from
a single neuron in the cortex.

00:41:48.290 --> 00:41:50.710
And they have the
animal-- in this

00:41:50.710 --> 00:41:53.760
it's, a cat-- in
an anechoic room.

00:41:53.760 --> 00:41:57.015
And they move the sound
source around in azimuth.

00:41:57.950 --> 00:42:00.450
We've talked about this with
experiments in the [INAUDIBLE].

00:42:03.140 --> 00:42:05.830
And they study the
neuron's response

00:42:05.830 --> 00:42:07.680
as a function of azimuth.

00:42:07.680 --> 00:42:11.195
In this particular study, they
also varied the sound level.

00:42:12.720 --> 00:42:15.150
And so that's what
the y-axis is here.

00:42:15.150 --> 00:42:16.560
This is the sound level axis.

00:42:18.030 --> 00:42:21.380
And what we just said is
that many neurons in cortex

00:42:21.380 --> 00:42:23.630
have a preferred sound level.

00:42:23.630 --> 00:42:26.510
They start to
increase their firing.

00:42:26.510 --> 00:42:28.960
And that's what's meant
by this shading here,

00:42:28.960 --> 00:42:32.380
the dark of the shading,
the higher the firing rate.

00:42:32.380 --> 00:42:36.420
And then at high sound
levels, the firing trails off,

00:42:36.420 --> 00:42:37.880
or it goes down to zero.

00:42:37.880 --> 00:42:41.096
This is a level function
for these different neurons.

00:42:42.968 --> 00:42:47.720
These are recordings now
from the auditory cortex

00:42:47.720 --> 00:42:50.750
within a single column.

00:42:50.750 --> 00:42:56.350
So shown here is the electrode
penetration going from unit

00:42:56.350 --> 00:42:58.960
one down two unit 10.

00:42:58.960 --> 00:43:03.415
And those are indicated here,
unit 1, down to unit 10.

00:43:05.030 --> 00:43:08.380
And the cortical layers are
indicated by the Roman numerals

00:43:08.380 --> 00:43:10.140
1 through 6 here.

00:43:10.140 --> 00:43:12.950
And they're recording
these 10 different neurons

00:43:12.950 --> 00:43:14.650
from a given cortical column.

00:43:17.110 --> 00:43:20.300
And what's impressive
about these studies is

00:43:20.300 --> 00:43:24.260
that the azimuth
of each of these

00:43:24.260 --> 00:43:27.230
neurons, where it
prefers in space,

00:43:27.230 --> 00:43:31.740
it is it a certain
azimuth, 45 to 90 degrees.

00:43:33.610 --> 00:43:35.670
And that's as if
you were recording

00:43:35.670 --> 00:43:37.890
from the left auditory cortex.

00:43:37.890 --> 00:43:41.214
45 degrees would be
over here, to 90 degrees

00:43:41.214 --> 00:43:42.380
would be straight over here.

00:43:43.580 --> 00:43:45.170
So these neurons
are going to respond

00:43:45.170 --> 00:43:48.980
when the speaker is in
a position over here.

00:43:48.980 --> 00:43:53.970
And they're going to respond
when there's a moderate sound

00:43:53.970 --> 00:43:55.110
level.

00:43:55.110 --> 00:43:58.980
Not the lowest level, and
not the highest level.

00:43:58.980 --> 00:44:01.990
So they prefer a
certain sound level.

00:44:01.990 --> 00:44:06.100
And within a given column,
almost all of the neurons

00:44:06.100 --> 00:44:09.335
have similar types of
azimuth level functions.

00:44:11.030 --> 00:44:12.950
And remember, before
we said that these all

00:44:12.950 --> 00:44:14.262
have about the same CF.

00:44:15.468 --> 00:44:20.490
So a second thing that is common
to units in a given column

00:44:20.490 --> 00:44:24.760
and auditory cortex is their
azimuth level response areas.

00:44:24.760 --> 00:44:26.180
And that's shown
very nicely here.

00:44:28.490 --> 00:44:33.360
These type of data suggests
that maybe these neurons

00:44:33.360 --> 00:44:36.590
play some kind of
role in telling us

00:44:36.590 --> 00:44:38.290
where a sound is coming from.

00:44:39.600 --> 00:44:41.630
Like without this
column, maybe we really

00:44:41.630 --> 00:44:44.100
wouldn't know that sound
sources were located

00:44:44.100 --> 00:44:47.980
at 45 to 90 degrees over there
on the contralateral hemifield.

00:44:49.680 --> 00:44:55.435
So there's been a lot of work
on auditory cortex and sound

00:44:55.435 --> 00:44:55.976
localization.

00:44:58.340 --> 00:45:00.420
And I want to get into it here.

00:45:00.420 --> 00:45:07.290
So how do experimenters
test behaviorally

00:45:07.290 --> 00:45:10.040
for how an animal
can localize sound?

00:45:11.280 --> 00:45:13.980
Well, this is the
formal way to do it.

00:45:13.980 --> 00:45:15.455
Here's an experimental animal.

00:45:16.490 --> 00:45:19.715
It's going to a speaker
that emitted a sound.

00:45:21.370 --> 00:45:25.600
Before, it had been sitting
in this central position

00:45:25.600 --> 00:45:27.110
in the testing cage here.

00:45:28.640 --> 00:45:30.980
Waiting maybe cued by
a light that's saying,

00:45:30.980 --> 00:45:32.460
the trial's about to start.

00:45:32.460 --> 00:45:33.925
And the animal then listens.

00:45:35.800 --> 00:45:40.300
And this speaker up here
near b didn't emit the sound.

00:45:40.300 --> 00:45:42.650
But the speaker down
here did emit the sound.

00:45:42.650 --> 00:45:44.980
And then the animal is
trained to go to the speaker

00:45:44.980 --> 00:45:47.540
that it had heard
emit the sound.

00:45:47.540 --> 00:45:51.690
If it does that correctly,
there's a little food reward

00:45:51.690 --> 00:45:54.745
area down below the speaker, and
the animal gets a food reward.

00:45:54.745 --> 00:45:56.290
And the animals
are food deprived,

00:45:56.290 --> 00:45:58.015
so they're motivated
to do this task.

00:45:59.250 --> 00:46:01.430
In this case, the
speakers can be moved.

00:46:03.340 --> 00:46:05.710
So you have removable speakers.

00:46:05.710 --> 00:46:10.060
Or you can have an array of
speakers, as indicated here.

00:46:11.450 --> 00:46:15.160
And the animal has to choose
which of the several speakers

00:46:15.160 --> 00:46:19.350
emitted the sound, and
go to the correct one

00:46:19.350 --> 00:46:21.480
to get the food reward.

00:46:21.480 --> 00:46:23.260
And this has been
done with a variety

00:46:23.260 --> 00:46:24.360
of experimental animals.

00:46:25.690 --> 00:46:27.390
In this case, it
looks like a cat.

00:46:27.390 --> 00:46:29.818
But they've also tested
rats and monkeys.

00:46:33.610 --> 00:46:36.960
Now, there's a couple things
you have to worry about here.

00:46:36.960 --> 00:46:40.460
You have to worry if your
sound is on a long time

00:46:40.460 --> 00:46:42.750
that the animal isn't cheating.

00:46:42.750 --> 00:46:44.990
And one way of cheating
would be for the animal

00:46:44.990 --> 00:46:48.510
to sit still here, and
listen to the sound,

00:46:48.510 --> 00:46:50.710
and then move a
little bit, maybe just

00:46:50.710 --> 00:46:52.620
by bending over, saying, OK.

00:46:52.620 --> 00:46:55.270
If I moved over here,
did the sound get louder?

00:46:55.270 --> 00:46:57.480
Oh, that means the sound
is coming from this side.

00:46:59.490 --> 00:47:02.000
So generally, these
tests are using

00:47:02.000 --> 00:47:05.555
pretty short stimulae--
50, 100 milliseconds.

00:47:06.740 --> 00:47:08.930
And during that
period, the animal

00:47:08.930 --> 00:47:13.560
doesn't have a chance to move
and sample the sound field.

00:47:15.630 --> 00:47:19.060
So what are the data in
normal hearing animals?

00:47:20.260 --> 00:47:26.200
75% correct at distinguishing
which of the speakers

00:47:26.200 --> 00:47:29.530
have emitted the
sound at 5 degrees.

00:47:29.530 --> 00:47:33.430
So in that case, it's
when the movable speaker's

00:47:33.430 --> 00:47:34.480
just 5 degrees.

00:47:35.820 --> 00:47:38.110
With a, in this
case, 500 millisecond

00:47:38.110 --> 00:47:40.420
long spectrally complex stimuli.

00:47:40.420 --> 00:47:44.980
So animals are not as good at
this sound localization task.

00:47:44.980 --> 00:47:48.530
In human performance, I think
back a few lectures ago,

00:47:48.530 --> 00:47:50.960
we talked about the minimum
audible angle in humans

00:47:50.960 --> 00:47:53.230
being a couple of degrees.

00:47:53.230 --> 00:47:54.155
Maybe 1 degree.

00:47:55.370 --> 00:47:57.475
In this case, the animal's
going to 5 degrees.

00:47:57.475 --> 00:47:59.900
So it's not quite as good.

00:48:01.340 --> 00:48:07.400
The animal can still do
the task surprisingly,

00:48:07.400 --> 00:48:10.790
even if it has just
one functioning ear.

00:48:12.350 --> 00:48:13.615
And how is that possible?

00:48:13.615 --> 00:48:15.570
Well, the animal's pinna.

00:48:15.570 --> 00:48:18.090
We talked about the
external ear or pinna,

00:48:18.090 --> 00:48:20.345
providing you some
nice spectral queues.

00:48:21.740 --> 00:48:25.860
And it looks like the spectrally
complex stimuli are being used.

00:48:25.860 --> 00:48:27.455
So those spectra
cues are available.

00:48:28.470 --> 00:48:31.940
But the minimum audible angle's
more like 10 to 12 degrees,

00:48:31.940 --> 00:48:34.690
with just one ear with
a good pinna on it.

00:48:36.150 --> 00:48:38.310
So the best performance
is with two ears.

00:48:39.400 --> 00:48:41.600
Now, why am I going
over this paradigm?

00:48:41.600 --> 00:48:46.230
Well, people have then
taken experimental animals

00:48:46.230 --> 00:48:47.810
and studied them after lesions.

00:48:49.450 --> 00:48:52.740
And we're talking about
the auditory cortex.

00:48:52.740 --> 00:48:58.670
So let's look at the results of
lesioning the auditory cortex

00:48:58.670 --> 00:49:00.130
on sound localization.

00:49:00.130 --> 00:49:03.190
So looks like in
this study, they're

00:49:03.190 --> 00:49:04.706
using the array of loudspeakers.

00:49:07.990 --> 00:49:12.190
The lesion is located
in the auditory cortex.

00:49:12.190 --> 00:49:15.980
And this is the right
side of the cortex.

00:49:15.980 --> 00:49:18.880
This is the occipital or
back part of the cortex.

00:49:18.880 --> 00:49:20.360
This is the front of the cortex.

00:49:20.360 --> 00:49:22.300
So the lesion is made
on the right side.

00:49:24.940 --> 00:49:27.460
When a lesion is made
on the right side

00:49:27.460 --> 00:49:30.480
of the auditory
cortex, the animal

00:49:30.480 --> 00:49:34.710
has problems localizing sound
in the opposite hemifield.

00:49:36.470 --> 00:49:38.670
So the lesion is made
on the right side.

00:49:40.110 --> 00:49:44.110
The animal doesn't know if it's
this speaker, this speaker,

00:49:44.110 --> 00:49:46.250
this speaker, or
this speaker that's

00:49:46.250 --> 00:49:50.170
emitting the sound as a random
performance on that side.

00:49:50.170 --> 00:49:53.250
However, the animal
can distinguish

00:49:53.250 --> 00:49:57.630
between the speakers in
the hemifield ipsilateral

00:49:57.630 --> 00:50:04.280
to the lesion, which suggests
that the intact auditory

00:50:04.280 --> 00:50:06.990
cortex is mediating
that behavior.

00:50:06.990 --> 00:50:09.240
So there's a deficit
contralaterally

00:50:09.240 --> 00:50:10.520
in the opposite hemifield.

00:50:11.900 --> 00:50:15.240
And as you can see from this
lesion, which was located smack

00:50:15.240 --> 00:50:20.660
in the middle of A1,
A1 lesions effectively

00:50:20.660 --> 00:50:22.810
knock out sound
localization behavior.

00:50:25.530 --> 00:50:28.050
So these early studies
suggested that A1

00:50:28.050 --> 00:50:32.020
is critically important, and
is necessary for correct sound

00:50:32.020 --> 00:50:33.125
localization behavior.

00:50:34.370 --> 00:50:36.770
And in these early
studies, the lesions

00:50:36.770 --> 00:50:41.610
were actually made surgically by
taking out some cortex tissue.

00:50:42.990 --> 00:50:47.510
And they became, as time
went on in the mid1980s,

00:50:47.510 --> 00:50:49.580
the lesion studies
became more elegant

00:50:49.580 --> 00:50:56.275
in that before the lesion was
made, frequency mapping of A1

00:50:56.275 --> 00:50:56.775
was made.

00:50:59.180 --> 00:51:01.680
And this frequency
mapping is shown here.

00:51:01.680 --> 00:51:04.766
This is best frequency, or CF.

00:51:04.766 --> 00:51:06.065
Those terms are synonymous.

00:51:07.770 --> 00:51:10.015
And this is distance
along the cortex.

00:51:11.580 --> 00:51:16.440
And not the entire auditory
cortex, field A1, was removed,

00:51:16.440 --> 00:51:21.470
but just a particular part,
just a little distance here.

00:51:21.470 --> 00:51:22.930
And it was known
from the mapping

00:51:22.930 --> 00:51:26.690
what CF was affected
by the lesion.

00:51:26.690 --> 00:51:28.915
And the other CFs
were left intact.

00:51:30.850 --> 00:51:34.570
You can test the animal for
any frequency you want to.

00:51:34.570 --> 00:51:38.830
So you can test for
frequencies in the intact area,

00:51:38.830 --> 00:51:42.430
or you can test for frequencies
in the lesioned area.

00:51:42.430 --> 00:51:48.180
And it was shown very clearly
then by plotting performance.

00:51:48.180 --> 00:51:50.390
This is a performance
axis, where

00:51:50.390 --> 00:51:52.640
downward is very accurate.

00:51:52.640 --> 00:51:56.070
This must be the number
of mistakes made.

00:51:56.070 --> 00:51:58.930
So 0 is no mistakes made.

00:51:58.930 --> 00:52:01.725
At the low frequencies
where the cortex is intact.

00:52:03.540 --> 00:52:06.910
At the midfrequencies, where
the cortex is lesioned,

00:52:06.910 --> 00:52:08.210
performance goes to chance.

00:52:09.720 --> 00:52:11.210
And then at the
high frequencies,

00:52:11.210 --> 00:52:13.910
again, where the
cortex is intact,

00:52:13.910 --> 00:52:17.310
the performance gets
very few errors.

00:52:17.310 --> 00:52:18.010
It's very good.

00:52:20.820 --> 00:52:24.760
So this elegant
experiment shows then

00:52:24.760 --> 00:52:29.250
that sound localization
proceeds by frequency

00:52:29.250 --> 00:52:30.210
independent channels.

00:52:32.430 --> 00:52:35.830
That is, the part of A1 that's
responsive to low frequencies

00:52:35.830 --> 00:52:39.850
is mediating low sound
frequency localization.

00:52:39.850 --> 00:52:42.670
And the part that's
responsive to high frequencies

00:52:42.670 --> 00:52:44.749
is mediating high frequency
sound localization.

00:52:44.749 --> 00:52:46.165
So a very beautiful
demonstration.

00:52:49.640 --> 00:52:54.050
Now, these lesions were
done with the techniques

00:52:54.050 --> 00:52:55.390
available at the time.

00:52:55.390 --> 00:52:59.005
And it's very simple to go in
and destroy a part of cortex.

00:53:00.450 --> 00:53:04.660
And for one reason
or another, people

00:53:04.660 --> 00:53:10.620
decided to revisit these
lesion experiments,

00:53:10.620 --> 00:53:12.370
even though they
were very convincing,

00:53:12.370 --> 00:53:14.595
done in many, many
different species.

00:53:15.850 --> 00:53:19.540
They decided to revisit them
with a completely different way

00:53:19.540 --> 00:53:20.395
of making a lesion.

00:53:22.510 --> 00:53:32.105
And this is the method of
inactivation by cooling.

00:53:34.610 --> 00:53:37.330
And maybe many of you
have heard of this.

00:53:37.330 --> 00:53:40.130
This might be the auditory
cortex, the surface.

00:53:40.130 --> 00:53:42.630
This is layer 1 and the
different cortical layers.

00:53:44.820 --> 00:53:48.590
The way you can
inactivate the cortex

00:53:48.590 --> 00:54:00.690
by cooling is by taking a piece
of tubing that has cooling

00:54:00.690 --> 00:54:02.820
fluid, or if you will, coolant.

00:54:06.020 --> 00:54:11.930
And you can put this coolant
with a pump through this tube,

00:54:11.930 --> 00:54:14.895
and you can lay the tube right
on the surface of the cortex.

00:54:16.010 --> 00:54:19.150
And obviously, as the
coolant comes through here,

00:54:19.150 --> 00:54:22.220
it's going to cool down
first the top layer

00:54:22.220 --> 00:54:25.270
of the cortex, and
then the lower layers.

00:54:25.270 --> 00:54:28.540
And finally, all of the cortex.

00:54:28.540 --> 00:54:33.760
And you can assure yourself that
this cooling has inactivated

00:54:33.760 --> 00:54:36.655
the cortex by doing things like
recording evoked potentials.

00:54:38.990 --> 00:54:42.260
And what's elegant about
the cooling experiments

00:54:42.260 --> 00:54:46.120
is that you can reverse them.

00:54:46.120 --> 00:54:48.230
So I don't know
if this is a word,

00:54:48.230 --> 00:54:53.410
but instead of coolant,
you can use a warmant,

00:54:53.410 --> 00:54:55.320
and restore this to
body temperature.

00:54:58.286 --> 00:54:59.910
And responses come back.

00:55:02.310 --> 00:55:06.600
And what's very impressive is
that these kinds of experiments

00:55:06.600 --> 00:55:09.570
can be done in animals
that are actually doing

00:55:09.570 --> 00:55:13.030
a behavioral task,
localizing sound.

00:55:15.650 --> 00:55:20.310
And clearly, those experiments
confirm these earlier lesion

00:55:20.310 --> 00:55:23.380
experiments that
if you cool A1, you

00:55:23.380 --> 00:55:26.510
get a deficit for a
localization ability

00:55:26.510 --> 00:55:27.890
in the contralateral hemifield.

00:55:29.040 --> 00:55:34.180
However, they have also come
up with an interesting result

00:55:34.180 --> 00:55:40.450
in that if you cool
some other fields,

00:55:40.450 --> 00:55:42.975
you also change sound
localization behavior.

00:55:45.820 --> 00:55:53.220
Field PAF, when cooled, also
interrupts sound localization

00:55:53.220 --> 00:55:53.820
behavior.

00:55:53.820 --> 00:55:55.190
So that's posterior to A1.

00:55:57.070 --> 00:56:01.440
And a small field
that's not named, but is

00:56:01.440 --> 00:56:06.320
right on top of the anterior
ectosylvian sulcus, the AES.

00:56:08.000 --> 00:56:11.800
When that area is cooled,
sound localization behavior's

00:56:11.800 --> 00:56:12.445
also disrupted.

00:56:14.010 --> 00:56:16.620
So I used to be
able to say, anyone

00:56:16.620 --> 00:56:20.770
who performs this critical
function, sound localization,

00:56:20.770 --> 00:56:23.260
well, not so sure
about it anymore.

00:56:23.260 --> 00:56:25.940
Because if you cool
these other fields,

00:56:25.940 --> 00:56:29.870
you have a disruption of
sound localization behavior.

00:56:29.870 --> 00:56:34.430
If you cool any of the other
fields like A2, of VPAF,

00:56:34.430 --> 00:56:36.482
or most of the
AAF, you don't get

00:56:36.482 --> 00:56:37.815
an interruption of the behavior.

00:56:38.920 --> 00:56:43.070
So what do we take
home from that?

00:56:43.070 --> 00:56:46.430
Well, it seems like there
are several fields that

00:56:46.430 --> 00:56:48.830
are important in sound
localization behavior.

00:56:50.320 --> 00:56:59.230
Looks like A1, p, or PAF
as it's sometimes called,

00:56:59.230 --> 00:57:07.565
and region near the
anterior ectosylvian sulcus

00:57:07.565 --> 00:57:08.315
are all important.

00:57:09.530 --> 00:57:11.590
And it's a little
bit controversial,

00:57:11.590 --> 00:57:14.720
why the old lesions
didn't actually show this.

00:57:14.720 --> 00:57:16.140
It seemed like in
the old lesions,

00:57:16.140 --> 00:57:19.060
there were some studies which
said, if you leave A1 intact,

00:57:19.060 --> 00:57:22.540
and you lesion all the
other cortical fields,

00:57:22.540 --> 00:57:24.670
the animal can
still do the task.

00:57:24.670 --> 00:57:27.100
That doesn't really fit with
the cooling results, which

00:57:27.100 --> 00:57:29.600
has several fields
that are important.

00:57:31.000 --> 00:57:35.230
So don't let me leave
you with the idea

00:57:35.230 --> 00:57:40.976
that what these fields do
is only sound localization

00:57:40.976 --> 00:57:41.475
behavior.

00:57:42.840 --> 00:57:45.790
So A1 may be involved
then hundreds

00:57:45.790 --> 00:57:48.600
of other tasks related
to our sense of hearing.

00:57:49.690 --> 00:57:51.545
It's also involved in
sound localization.

00:57:53.160 --> 00:57:56.400
So that's the right
way to think about it,

00:57:56.400 --> 00:57:58.910
that these fields
probably do many things.

00:57:58.910 --> 00:58:03.310
And I think if you got the gist
of what Doctor Schiller talked

00:58:03.310 --> 00:58:07.140
about in vision, he's not a
big fan of this little area

00:58:07.140 --> 00:58:09.090
of cortex does this
little function.

00:58:09.090 --> 00:58:11.250
And over here, this little
area does this function.

00:58:11.250 --> 00:58:16.950
He's more of a believer in
holistic cortex function

00:58:16.950 --> 00:58:20.780
where to do a task, you
employ a lot of cortex;

00:58:20.780 --> 00:58:23.195
auditory cortex if you're
doing an auditory task.

00:58:24.210 --> 00:58:26.840
And perhaps the more
difficult a task is,

00:58:26.840 --> 00:58:28.230
the motor cortex you use.

00:58:29.460 --> 00:58:30.940
We'll see an evidence of that.

00:58:30.940 --> 00:58:35.110
And next time, when we talk
about language processing

00:58:35.110 --> 00:58:36.800
in humans from imaging studies.

00:58:38.960 --> 00:58:44.760
So what else does cortex do
besides sound localization?

00:58:51.424 --> 00:58:53.870
Oh, I forgot to talk
about auditory cortex

00:58:53.870 --> 00:58:57.300
in humans, how many
tonotopic fields there are.

00:58:57.300 --> 00:59:02.895
So I brought this nice
model of the primate brain.

00:59:04.170 --> 00:59:07.265
And where is auditory
cortex in humans?

00:59:08.470 --> 00:59:11.510
So this is a slice
of the brain, as

00:59:11.510 --> 00:59:13.320
if you were to cut it like this.

00:59:13.320 --> 00:59:15.320
And look at one slice.

00:59:15.320 --> 00:59:19.000
And this is the right
and left temporal lobes.

00:59:19.000 --> 00:59:22.640
So in the primate, you have
actually a separate lobe

00:59:22.640 --> 00:59:24.320
of the brain called
the temporal lobe.

00:59:25.860 --> 00:59:30.810
And in the temporal lobe,
you have to-- the primate

00:59:30.810 --> 00:59:32.880
is a little bit more
difficult to examine

00:59:32.880 --> 00:59:37.490
than the cat-- you have to pull
down the sylvian fissure, which

00:59:37.490 --> 00:59:39.660
is between-- separates
the temporal lobe

00:59:39.660 --> 00:59:42.150
from the parietal
cortex up here,

00:59:42.150 --> 00:59:47.470
and look on the superior
surface of the temporal lobe,

00:59:47.470 --> 00:59:48.740
and find the sight of A1.

00:59:50.720 --> 00:59:55.560
And on that superior
temporal lobe surface,

00:59:55.560 --> 01:00:00.150
you have a little gyrus that was
examined by an animus Heschl.

01:00:00.150 --> 01:00:02.810
And Heschl's gyrus in
humans is the site of A1.

01:00:05.750 --> 01:00:10.670
Some humans actually
have 2 Heschl's, gyri,

01:00:10.670 --> 01:00:14.710
and they have their
A1 either on one

01:00:14.710 --> 01:00:19.710
or both of the Heschl's gyri.

01:00:20.890 --> 01:00:26.090
Now, looking at it from the
side view, in the temporal lobe,

01:00:26.090 --> 01:00:29.060
you have the 3 big gyri.

01:00:29.060 --> 01:00:33.520
Superior temporal gyrus,
inferior temporal gyrus--

01:00:33.520 --> 01:00:36.980
sorry, middle temporal gyrus,
and inferior temporal gyrus.

01:00:36.980 --> 01:00:40.090
And so A1 is on the
superior surface

01:00:40.090 --> 01:00:43.725
of the superior temporal
gyrus on a little bitty gyrus

01:00:43.725 --> 01:00:45.140
called Heschls.

01:00:45.140 --> 01:00:48.050
So I'm going to pass
this model around.

01:00:48.050 --> 01:00:51.060
And A1 is indicated by a little
piece of yellow tape there.

01:00:51.060 --> 01:00:53.460
You can take a look at it.

01:00:53.460 --> 01:00:58.740
And so that area,
Heschl's gyrus,

01:00:58.740 --> 01:01:01.350
lights up very nicely
in imaging studies

01:01:01.350 --> 01:01:04.070
when you present
auditory stimuli.

01:01:04.070 --> 01:01:08.890
And so here's an imaging study
where the imaging plane was

01:01:08.890 --> 01:01:13.530
parallel to the sylvian
fissure or sylvian sulcus,

01:01:13.530 --> 01:01:16.750
and it's capturing just this
superior temporal gyrus.

01:01:17.900 --> 01:01:19.620
And the plane is
looking down here.

01:01:19.620 --> 01:01:23.200
And on Heschl's gyrus, you
see the left and the right

01:01:23.200 --> 01:01:27.020
in this case, and just the
right in this case lighting up.

01:01:29.020 --> 01:01:33.220
And you can use, of course,
different frequency sounds.

01:01:36.260 --> 01:01:39.700
And change the
frequencies of those

01:01:39.700 --> 01:01:44.640
sounds in a progression
from high frequencies

01:01:44.640 --> 01:01:45.590
to low frequencies.

01:01:46.630 --> 01:01:48.650
And you can draw
the progressions

01:01:48.650 --> 01:01:51.140
that you see in imaging
signals, and that's

01:01:51.140 --> 01:01:52.595
what's drawn with these arrows.

01:01:53.930 --> 01:01:56.785
This is a MIT thesis
by Tom Talavage.

01:01:58.350 --> 01:02:00.520
And he showed that
there were at least 1,

01:02:00.520 --> 01:02:07.110
2, 3, 4, 5 clear progressions
of frequency sensitivity,

01:02:07.110 --> 01:02:09.800
as if you were progressing
along tonotopically

01:02:09.800 --> 01:02:13.660
mapped auditory cortical
fields in the human.

01:02:13.660 --> 01:02:19.130
So remember, we saw 4
tonotopically mapped fields

01:02:19.130 --> 01:02:19.860
in the cat.

01:02:19.860 --> 01:02:24.300
And here we have at least
4, perhaps 5 in humans.

01:02:25.760 --> 01:02:28.935
This one is labeled HG,
that's Heschl's gyrus.

01:02:30.670 --> 01:02:33.100
And that's probably
primary auditory cortex.

01:02:34.800 --> 01:02:38.690
This is a view looking down
on the superior surface

01:02:38.690 --> 01:02:39.720
of the temporal lobe.

01:02:39.720 --> 01:02:42.380
And this is what's
called an inflated view.

01:02:43.420 --> 01:02:46.020
So it's like taking
that cortex model

01:02:46.020 --> 01:02:48.370
and blowing it up
like a balloon.

01:02:48.370 --> 01:02:52.260
And so the gyri are indicated
by the lighter shading,

01:02:52.260 --> 01:02:57.125
and the sulci are indicated
by the more dark shading.

01:02:57.125 --> 01:02:59.910
So that's what that is.

01:02:59.910 --> 01:03:01.260
These are the dimensions here.

01:03:01.260 --> 01:03:03.740
Posterior lateral
is that direction.

01:03:03.740 --> 01:03:08.270
So we have multiple
tonotopically organized areas

01:03:08.270 --> 01:03:09.955
in human auditory cortex.

01:03:11.580 --> 01:03:17.190
Now, the paper that we read for
today's class by Penagos et al

01:03:17.190 --> 01:03:25.800
talks about a center near A1,
near Heschl's gyrus, which

01:03:25.800 --> 01:03:30.380
lights up in imaging studies
when the subject is presented

01:03:30.380 --> 01:03:33.880
with sounds that have a
strong cessation of pitch.

01:03:34.990 --> 01:03:37.250
So we talked about pitch
a little bit earlier

01:03:37.250 --> 01:03:37.800
in the class.

01:03:37.800 --> 01:03:40.130
And this is the
slide that I showed.

01:03:40.130 --> 01:03:42.420
And it has a
different title now.

01:03:42.420 --> 01:03:47.622
I think it was titled something
like complicated sounds,

01:03:47.622 --> 01:03:48.580
or something like that.

01:03:48.580 --> 01:03:52.510
Well, a complex sound
is simply a sound

01:03:52.510 --> 01:03:54.035
that has multiple frequencies.

01:03:55.560 --> 01:03:57.970
And so the stimulate
used in the paper

01:03:57.970 --> 01:04:00.890
are complex sounds in that
they have multiple frequencies.

01:04:02.750 --> 01:04:05.060
Earlier, we talk
about this in terms

01:04:05.060 --> 01:04:07.700
of the context of
musical sounds.

01:04:07.700 --> 01:04:11.796
Musical sounds almost always
have a fundamental frequency,

01:04:11.796 --> 01:04:13.296
and then a whole
bunch of harmonics.

01:04:15.120 --> 01:04:19.600
And to have a strong
sensation of pitch,

01:04:19.600 --> 01:04:24.930
these musical sounds have
a very tight relationship

01:04:24.930 --> 01:04:27.050
of the fundamental
and the harmonics.

01:04:27.050 --> 01:04:29.550
They can't be a
random relationship.

01:04:29.550 --> 01:04:32.150
They actually have to be
multiples of the fundamental.

01:04:33.260 --> 01:04:52.140
For example, this complex of
tones, 100 hertz, 200 hertz,

01:04:52.140 --> 01:04:59.850
300 hertz, 400, and so on,
are multiples of one another.

01:04:59.850 --> 01:05:04.080
But if you had the
fundamental be 100,

01:05:04.080 --> 01:05:10.070
the next harmonic be 150,
the next harmonic be 190,

01:05:10.070 --> 01:05:13.070
the next harmonic be
230, where they're not

01:05:13.070 --> 01:05:15.870
multiples of one another,
that stimulus would not

01:05:15.870 --> 01:05:18.576
have a strong pitch
associated with it.

01:05:21.240 --> 01:05:25.680
These musical sounds are
interesting because they

01:05:25.680 --> 01:05:27.580
have a strong pitch.

01:05:27.580 --> 01:05:29.790
The pitch is almost
always related

01:05:29.790 --> 01:05:32.920
to the lowest, or fundamental
frequency of them.

01:05:34.060 --> 01:05:36.050
And the pitch is very invariant.

01:05:36.050 --> 01:05:39.860
As long as you have this nice
pattern of harmonics that

01:05:39.860 --> 01:05:43.000
are related to each
other by multiples,

01:05:43.000 --> 01:05:48.140
the pitch of this, no, which
I think is a piano note,

01:05:48.140 --> 01:05:52.660
and the pitch of this note,
which-- let's do these two.

01:05:52.660 --> 01:05:55.924
This is a guitar sound, and
this is an alto saxophone sound

01:05:55.924 --> 01:05:57.340
where the fundamental
is the same.

01:05:58.800 --> 01:06:01.760
The harmonic amplitude
is completely different.

01:06:03.550 --> 01:06:06.755
But we recognize them as
playing the same pitch.

01:06:08.690 --> 01:06:11.240
You can play a lot
around with the amplitude

01:06:11.240 --> 01:06:12.250
of these harmonics.

01:06:12.250 --> 01:06:13.415
I drew them all the same.

01:06:14.640 --> 01:06:16.995
But clearly, they
can be any jumble

01:06:16.995 --> 01:06:21.080
of pattern, as long as they're
multiples of one another.

01:06:21.080 --> 01:06:24.290
You hear this as having
the same pitch as that.

01:06:24.290 --> 01:06:26.440
And pitch is very
invariant to things

01:06:26.440 --> 01:06:28.710
like where the sound
is coming from.

01:06:28.710 --> 01:06:34.340
Pitch is invariant to how
high and level the sound is.

01:06:34.340 --> 01:06:38.400
So pitch is a very fundamental
attribute of the sound.

01:06:38.400 --> 01:06:41.340
Defined in the
psychophysics textbook

01:06:41.340 --> 01:06:46.320
is, pitch is that attribute
of auditory sensation in terms

01:06:46.320 --> 01:06:49.540
of which sounds may be
ordered on a musical scale.

01:06:49.540 --> 01:06:53.570
So this one's low, this one's
middle, and this one's high.

01:06:53.570 --> 01:06:56.910
And so when cochlear implant
users are programmed first,

01:06:56.910 --> 01:07:00.780
they take this electrode,
and they stimulate it.

01:07:00.780 --> 01:07:03.240
And the user says, yeah,
that sounds like a low one.

01:07:03.240 --> 01:07:06.140
Then they activate
the next electrode.

01:07:06.140 --> 01:07:08.765
And the audiologist
says, is this one higher,

01:07:08.765 --> 01:07:10.720
or is this one lower?

01:07:10.720 --> 01:07:15.090
And if it's higher, then they
route their speech processor,

01:07:15.090 --> 01:07:16.875
higher frequencies,
into that electrode.

01:07:19.650 --> 01:07:22.455
So they do a pitch ranking
in an auditory implants.

01:07:24.240 --> 01:07:27.100
Now, pitch of the
complicated sound

01:07:27.100 --> 01:07:29.130
depends strongly on the
fundamental frequency.

01:07:29.130 --> 01:07:30.470
Everybody knows that.

01:07:30.470 --> 01:07:34.880
Wow, you can play little
tricks in these stimuli.

01:07:34.880 --> 01:07:38.180
You can do something like remove
the fundamental frequency.

01:07:40.000 --> 01:07:41.450
How does that change the pitch?

01:07:41.450 --> 01:07:44.335
Well, this guy becomes
the new fundamental.

01:07:46.080 --> 01:07:47.510
That's what you might think.

01:07:47.510 --> 01:07:50.520
But actually, removing
this fundamental

01:07:50.520 --> 01:07:54.250
is just like playing around
with the amplitude of the higher

01:07:54.250 --> 01:07:54.840
frequencies.

01:07:54.840 --> 01:07:56.430
It doesn't change
the pitch at all.

01:07:57.530 --> 01:07:59.730
And this is called the
missing fundamental.

01:08:07.930 --> 01:08:11.600
And that's actually lucky
for cheap speakers that

01:08:11.600 --> 01:08:12.970
might not have a very good base.

01:08:14.320 --> 01:08:16.120
The fundamental is
hardly there at all,

01:08:16.120 --> 01:08:18.810
but the piece still
sounds musical,

01:08:18.810 --> 01:08:23.000
and it's not changed a lot.

01:08:23.000 --> 01:08:24.810
Or why does that happen?

01:08:24.810 --> 01:08:31.050
Well, this very nice multiples
of 100 is still present.

01:08:31.050 --> 01:08:36.060
And so the temporal pattern
of all these harmonics, if you

01:08:36.060 --> 01:08:43.640
add them up and look at this
thing in the time domain--

01:08:43.640 --> 01:08:45.610
remember, this was
a graph frequency.

01:08:47.970 --> 01:08:51.680
Whatever this looks
like, it's going

01:08:51.680 --> 01:08:54.439
to repeat after 10 milliseconds.

01:08:54.439 --> 01:08:56.890
Because it's period
is still 100 hertz.

01:08:58.029 --> 01:09:00.660
I'm not a very good artist,
but it's going to be the same.

01:09:00.660 --> 01:09:02.939
And it's going to
be the same here.

01:09:02.939 --> 01:09:07.170
So each 10 milliseconds, it's
going to repeat its pattern.

01:09:07.170 --> 01:09:12.989
It has the same regularity, even
if you remove the fundamental.

01:09:14.300 --> 01:09:15.520
Now, you may not believe me.

01:09:15.520 --> 01:09:16.978
So let me give you
a demonstration.

01:09:18.040 --> 01:09:19.580
And in this
demonstration, there's

01:09:19.580 --> 01:09:21.925
a whole bunch of harmonics
presented at first.

01:09:23.250 --> 01:09:25.180
And then in the
second presentation,

01:09:25.180 --> 01:09:27.140
they remove the fundamental.

01:09:27.140 --> 01:09:29.490
And you should listen
to see if the pitch

01:09:29.490 --> 01:09:32.990
that your ears hear
changes at all.

01:09:32.990 --> 01:09:37.720
On the second presentation,
they remove this next harmonic,

01:09:37.720 --> 01:09:39.010
and so on, and so forth.

01:09:39.010 --> 01:09:41.310
And I think they
end up with removing

01:09:41.310 --> 01:09:44.069
four different
harmonics after they

01:09:44.069 --> 01:09:46.760
present the complete stimulus.

01:09:46.760 --> 01:09:50.395
So listen to this demonstration
of the missing fundamental.

01:09:50.395 --> 01:09:51.311
[AUDIO PLAYBACK]

01:09:51.311 --> 01:09:54.007
-Pitch of the missing
fundamental, or virtual pitch.

01:09:55.410 --> 01:09:59.470
You will hear a complex tone
with 10 harmonics, first

01:09:59.470 --> 01:10:03.380
complete, and then with the
lower harmonics successively

01:10:03.380 --> 01:10:04.165
removed.

01:10:04.165 --> 01:10:05.852
Does the pitch of
the complex change?

01:10:06.890 --> 01:10:08.740
The demonstration
is repeated once.

01:10:11.680 --> 01:10:16.090
[SERIES OF PITCHES]

01:10:32.260 --> 01:10:33.290
[END AUDIO PLAYBACK]

01:10:33.290 --> 01:10:35.930
PROFESSOR: I think
it's pretty clear.

01:10:35.930 --> 01:10:38.130
Does everybody want
to discuss this?

01:10:38.130 --> 01:10:40.810
So when you lose
these first 1 or 2,

01:10:40.810 --> 01:10:43.190
the pitch doesn't
change a great deal.

01:10:43.190 --> 01:10:45.420
But by the end of
the demo, this pitch

01:10:45.420 --> 01:10:46.905
is starting to
sound a lot higher.

01:10:48.460 --> 01:10:51.570
So if you move some of
these around or decrease

01:10:51.570 --> 01:10:54.190
their amplitude, this
one's a low fundamental.

01:10:54.190 --> 01:10:55.890
The pitch doesn't
change a great deal.

01:10:57.060 --> 01:11:01.820
Now, that is what
they did in the paper

01:11:01.820 --> 01:11:02.895
that we read for today.

01:11:04.790 --> 01:11:07.190
What they do is they
have a complex tone

01:11:07.190 --> 01:11:08.650
with a whole bunch of harmonics.

01:11:11.010 --> 01:11:13.830
And they do a clever
thing like they've

01:11:13.830 --> 01:11:15.340
done on this demonstration.

01:11:15.340 --> 01:11:17.570
They just select
some of the harmonics

01:11:17.570 --> 01:11:21.470
to present to the observers
in the imaging study.

01:11:23.610 --> 01:11:26.740
And the cleverness
of this study is

01:11:26.740 --> 01:11:32.380
that by clever filtering
of this harmonic pattern,

01:11:32.380 --> 01:11:34.720
they can give you
some stimulae that

01:11:34.720 --> 01:11:37.330
have really strong
sensations of pitch.

01:11:38.400 --> 01:11:40.680
Or in this one
case, which I think

01:11:40.680 --> 01:11:46.040
is condition 2, a very weak
sensation of pitch because

01:11:46.040 --> 01:11:48.130
of the particular
harmonics they've chosen.

01:11:50.170 --> 01:11:52.450
So they have 3 stimulate.

01:11:52.450 --> 01:11:54.710
They giving you a strong
sensation of pitch,

01:11:54.710 --> 01:11:57.520
and one that has a very weak
sensation of pitch because

01:11:57.520 --> 01:12:00.340
of the clever way
they've filtered it.

01:12:00.340 --> 01:12:04.690
And further clevering,
all of these stimulae

01:12:04.690 --> 01:12:06.570
have the same regularity.

01:12:06.570 --> 01:12:10.000
They have the same
regularity in terms

01:12:10.000 --> 01:12:11.340
of their temporal waveform.

01:12:12.360 --> 01:12:14.560
So the cleverness
of this study then

01:12:14.560 --> 01:12:16.660
is that the temporal
waveform hasn't

01:12:16.660 --> 01:12:19.800
changed in terms
of its regularity.

01:12:19.800 --> 01:12:22.270
But the subject's
impression of the pitch,

01:12:22.270 --> 01:12:27.590
whether it's a strong pitch
or a weak pitch, has changed.

01:12:27.590 --> 01:12:29.790
So by weak pitch,
I mean something

01:12:29.790 --> 01:12:32.620
that sounds like a
noise, or a click.

01:12:32.620 --> 01:12:35.230
Those stimulate don't have
strong sensation of pitch

01:12:35.230 --> 01:12:36.390
because they're random.

01:12:36.390 --> 01:12:39.170
They don't have this nice
pattern of harmonics.

01:12:40.460 --> 01:12:46.770
So I wasn't convinced by
this verbiage and the figure.

01:12:46.770 --> 01:12:51.730
So I decided I wanted to
listen to these stimuli myself.

01:12:51.730 --> 01:12:54.940
And it was convenient, because
I know all three authors.

01:12:54.940 --> 01:12:58.810
So Hector Penagos, when
he wrote this paper,

01:12:58.810 --> 01:13:02.300
was a graduate student
in the speech and hearing

01:13:02.300 --> 01:13:03.925
bioscience and
technology program.

01:13:05.730 --> 01:13:08.040
Jennifer Melcher
is a faculty member

01:13:08.040 --> 01:13:09.450
over at the Eaton-Peabody Lab.

01:13:09.450 --> 01:13:11.860
Her office is
right next to mine.

01:13:11.860 --> 01:13:16.157
And Andrew Oxenham was a
faculty member here at MIT,

01:13:16.157 --> 01:13:18.115
and has since moved to
University of Minnesota.

01:13:19.320 --> 01:13:23.290
So I started asking the
authors, because they're

01:13:23.290 --> 01:13:25.877
all friends of mine, if
I could have the demos.

01:13:25.877 --> 01:13:27.960
And one of them said, well,
it's been a long time.

01:13:27.960 --> 01:13:29.350
I'm not sure I still have them.

01:13:30.380 --> 01:13:32.600
And the other author,
is the second author

01:13:32.600 --> 01:13:34.300
I went to-- I won't
say who it is,

01:13:34.300 --> 01:13:35.680
said, I got them right away.

01:13:35.680 --> 01:13:39.200
So he sent them-- that author
sent them to me right away.

01:13:40.300 --> 01:13:43.420
And so I have them, and
I'll play them for you.

01:13:43.420 --> 01:13:46.000
Now, you'll listen
to these stimuli.

01:13:46.000 --> 01:13:47.594
And what was
surprising to me that I

01:13:47.594 --> 01:13:49.260
didn't get from the
methods of the paper

01:13:49.260 --> 01:13:52.540
is that they don't just keep
presenting the same thing over

01:13:52.540 --> 01:13:53.060
and over.

01:13:53.060 --> 01:13:54.970
The pitch actually moves around.

01:13:54.970 --> 01:13:58.000
And that's one of the
nice parts of this demo

01:13:58.000 --> 01:14:01.720
is that you can actually tell
that the pitch is moving around

01:14:01.720 --> 01:14:04.270
in the ones with strong
sensation of pitch.

01:14:05.430 --> 01:14:08.480
Second thing that
they did was, they

01:14:08.480 --> 01:14:12.470
added a little bit of
background noise to these.

01:14:12.470 --> 01:14:14.700
And it turns out
that when you present

01:14:14.700 --> 01:14:17.410
a whole bunch of harmonics
with the speaker,

01:14:17.410 --> 01:14:19.955
the speaker will introduce
a little distortion.

01:14:19.955 --> 01:14:22.230
Your ear introduces distortion.

01:14:22.230 --> 01:14:25.160
And they wanted to mask
that distortion out.

01:14:25.160 --> 01:14:27.780
And the distortion is
pretty low in level.

01:14:27.780 --> 01:14:30.240
And so this noise that's
a continuous background

01:14:30.240 --> 01:14:32.570
is a pretty effective mask.

01:14:32.570 --> 01:14:36.580
I think you can still hear that
these stimuli, in some cases,

01:14:36.580 --> 01:14:39.517
have pretty strong
sensations of pitch.

01:14:39.517 --> 01:14:41.850
So I'm going to start out
with condition one, which they

01:14:41.850 --> 01:14:43.915
say has a strong
sensation of pitch.

01:14:43.915 --> 01:14:46.406
And you can judge for
yourself, whether you

01:14:46.406 --> 01:14:48.604
hear the pitch moving around.

01:14:48.604 --> 01:14:52.076
[PITCH WITH STATIC]

01:15:13.404 --> 01:15:15.388
PROFESSOR: Maybe it
will go on forever.

01:15:15.388 --> 01:15:17.372
I don't know how long
it would go on for.

01:15:18.390 --> 01:15:20.575
Well, anyway, could you
hear those moving around?

01:15:20.575 --> 01:15:21.982
You could rank them.

01:15:23.460 --> 01:15:24.460
Here's number 2.

01:15:24.460 --> 01:15:27.890
[PITCH WITH STATIC]

01:15:27.890 --> 01:15:30.510
PROFESSOR: It's
moving around, right?

01:15:30.510 --> 01:15:32.280
Number 3.

01:15:32.280 --> 01:15:35.837
[LOWER PITCH WITH STATIC]

01:15:35.837 --> 01:15:36.420
PROFESSOR: OK.

01:15:36.420 --> 01:15:40.170
Now, to me, those have strong
sensations of pitch, I believe.

01:15:40.170 --> 01:15:41.314
I'm a believer.

01:15:41.314 --> 01:15:42.730
Now, here's the
last one that they

01:15:42.730 --> 01:15:44.302
say has a weak [INAUDIBLE].

01:15:44.302 --> 01:15:48.166
[PITCH WITH STATIC]

01:15:54.837 --> 01:15:55.420
PROFESSOR: OK.

01:15:55.420 --> 01:15:59.890
So at first, I was expecting to
hear no change in pitch at all.

01:15:59.890 --> 01:16:02.090
But actually, the pitches
change a little bit.

01:16:02.090 --> 01:16:05.970
And so when you go back and say,
it's a weak sensation of pitch,

01:16:05.970 --> 01:16:06.711
OK.

01:16:06.711 --> 01:16:07.210
Right?

01:16:07.210 --> 01:16:08.001
So we're believers?

01:16:08.940 --> 01:16:14.350
Or does anybody want
to say-- all right.

01:16:14.350 --> 01:16:16.500
What happened in
their imaging study?

01:16:16.500 --> 01:16:19.380
Well, this is
pretty small figure.

01:16:19.380 --> 01:16:22.160
But it summarizes the
results in that they

01:16:22.160 --> 01:16:25.970
had an activation of
the circled area, which

01:16:25.970 --> 01:16:31.870
is near Heschl's gyrus-- just,
I believe, anterior to it.

01:16:31.870 --> 01:16:35.550
And this is the place that
had a high activation.

01:16:36.630 --> 01:16:38.905
In the cases of the
stimuli, was strong.

01:16:40.400 --> 01:16:43.750
Psychophysical
sensations of pitch,

01:16:43.750 --> 01:16:46.270
but had a low
activation in the case

01:16:46.270 --> 01:16:49.390
where there was a weak
sensation of pitch.

01:16:49.390 --> 01:16:51.900
Other areas of the
brain-- for example,

01:16:51.900 --> 01:16:56.860
Heschl's gyrus lit up for
all of the conditions.

01:16:58.250 --> 01:17:00.540
And what's interesting
about this study

01:17:00.540 --> 01:17:04.520
is they examined some of
the subcortical nuclei

01:17:04.520 --> 01:17:05.770
that we've been talking about.

01:17:05.770 --> 01:17:10.480
For example, the inferior
colliculus and the cochlear

01:17:10.480 --> 01:17:10.980
nuclei.

01:17:12.280 --> 01:17:16.750
And these are the activations
for those centers.

01:17:16.750 --> 01:17:19.310
Cochlear nucleus activates
pretty much the same

01:17:19.310 --> 01:17:21.680
for all of the conditions.

01:17:21.680 --> 01:17:23.800
This black one is the
one that was associated

01:17:23.800 --> 01:17:26.000
with the weak
sensation of pitch.

01:17:26.000 --> 01:17:28.250
The inferior colliculus,
perhaps a little bit less

01:17:28.250 --> 01:17:33.170
activation for that stimulus,
but not significantly so.

01:17:33.170 --> 01:17:37.430
In the case of this center
for pitched salience

01:17:37.430 --> 01:17:40.355
in the auditory cortex, clearly
there's a lot less activation.

01:17:41.750 --> 01:17:45.320
For that stimulus with the
weak sensation of pitch,

01:17:45.320 --> 01:17:48.210
about the same amount
of activation as you'd

01:17:48.210 --> 01:17:50.737
find with noise bursts there.

01:17:52.380 --> 01:17:54.700
So that, I think,
clearly demonstrates,

01:17:54.700 --> 01:17:56.790
and other imaging
studies have clearly

01:17:56.790 --> 01:18:00.690
demonstrated that this area
is the region of cortex that

01:18:00.690 --> 01:18:04.180
becomes very active when
we experience stimuli

01:18:04.180 --> 01:18:05.710
with strong sensations of pitch.

01:18:07.220 --> 01:18:10.480
In experimental animals,
recordings from, for example,

01:18:10.480 --> 01:18:13.430
the marmoset auditory cortex.

01:18:13.430 --> 01:18:17.690
You find neurons in
an equivalent area

01:18:17.690 --> 01:18:22.880
that respond very nicely
to harmonic complexes that

01:18:22.880 --> 01:18:25.190
have strong
sensation of pitches.

01:18:25.190 --> 01:18:29.030
If you remove too
many of the harmonics

01:18:29.030 --> 01:18:32.905
where the pitch changes a
lot, the neurons fire less.

01:18:35.070 --> 01:18:38.030
And clearly, in those
cases, remember,

01:18:38.030 --> 01:18:40.540
most neurons in the
cortex are finally

01:18:40.540 --> 01:18:42.550
tuned to sound frequency.

01:18:42.550 --> 01:18:45.070
You can remove a whole bunch
of these lower harmonics,

01:18:45.070 --> 01:18:48.970
and not change the response,
suggesting that there is really

01:18:48.970 --> 01:18:53.100
signaling, that there is pitch
associated with that stimulus

01:18:53.100 --> 01:18:55.614
rather than there's a
certain kind of frequency.

01:18:58.850 --> 01:19:01.720
So that's the bottom
line for this study.

01:19:01.720 --> 01:19:03.910
Let me just mention
a couple things that

01:19:03.910 --> 01:19:07.270
make auditory
experiments difficult

01:19:07.270 --> 01:19:08.920
when you're trying
to image the brain.

01:19:08.920 --> 01:19:12.605
Has anybody listened
to an fMRI machine?

01:19:12.605 --> 01:19:13.105
An imager?

01:19:14.700 --> 01:19:16.515
Very loud, right?

01:19:17.740 --> 01:19:21.310
So you have problems
with the subjects

01:19:21.310 --> 01:19:25.050
listening to the stimulus that
you intend to present to them

01:19:25.050 --> 01:19:29.435
rather than listening to
the imaging noise itself.

01:19:29.435 --> 01:19:35.500
And so in this study,
they went to great extent

01:19:35.500 --> 01:19:38.265
to try to reduce
the imaging noise.

01:19:39.460 --> 01:19:45.660
The subjects were wearing
protective earmuffs,

01:19:45.660 --> 01:19:47.950
and the stimulae
were loudspeakers

01:19:47.950 --> 01:19:51.600
that led to those
earmuffs in long tubes.

01:19:51.600 --> 01:19:55.100
Of course, you can't have a
speaker right near the ear

01:19:55.100 --> 01:19:57.445
because there's a magnet
associated with the speaker.

01:19:57.445 --> 01:19:59.570
So you have to have the
speaker outside the imager.

01:20:01.110 --> 01:20:05.115
So they actually turned one
of the imaging pumps off.

01:20:07.350 --> 01:20:11.950
There is a lot of challenge in
imaging such small structures

01:20:11.950 --> 01:20:14.270
as the cochlear nuclei
in inferior colliculus.

01:20:15.350 --> 01:20:18.150
And they said to improve
the detection of activation

01:20:18.150 --> 01:20:20.780
in these brainstem
[? structures, ?]

01:20:20.780 --> 01:20:24.050
the data were activated
using cardiac triggering.

01:20:24.050 --> 01:20:25.790
So does anybody know
what that means?

01:20:28.490 --> 01:20:33.630
Well, when your heart beats,
it pulses on all the arteries,

01:20:33.630 --> 01:20:36.080
and actually moves
the brainstem.

01:20:36.080 --> 01:20:38.670
Brainstem is so small,
it can be moved.

01:20:38.670 --> 01:20:41.920
Cortex is moving too, but the
areas are generally bigger.

01:20:41.920 --> 01:20:46.930
And so if you weren't going
to take care of the heartbeat,

01:20:46.930 --> 01:20:48.590
the brainstem might
be imaged when

01:20:48.590 --> 01:20:50.280
it was in this
position at one point.

01:20:50.280 --> 01:20:53.270
And the next image might,
when it was over here.

01:20:54.490 --> 01:20:57.650
So what cardiac
triggering is, they

01:20:57.650 --> 01:20:59.840
record the EKG from the subject.

01:21:01.050 --> 01:21:04.620
And when they see the
QRS complex, or whatever

01:21:04.620 --> 01:21:07.260
waveform from the
EKG, and they say,

01:21:07.260 --> 01:21:09.035
that's the time
to take the image.

01:21:09.035 --> 01:21:11.720
So they only take the
image at a certain point

01:21:11.720 --> 01:21:13.920
relative to the cardiac cycle.

01:21:13.920 --> 01:21:15.930
So the brain, even
though it's moving,

01:21:15.930 --> 01:21:17.875
it's always moved in
this certain position.

01:21:19.200 --> 01:21:22.640
So that's a challenge
that's associated

01:21:22.640 --> 01:21:26.270
with imaging small structures
like these brainstem nuclei.

01:21:33.470 --> 01:21:35.250
So then, another
property, at least

01:21:35.250 --> 01:21:37.350
of this field of
the auditory cortex,

01:21:37.350 --> 01:21:42.130
is to process stimulae that
to have high pitch salience.

01:21:42.130 --> 01:21:45.140
So we've had two functions
associated with auditory cortex

01:21:45.140 --> 01:21:47.220
then, just as a summary here.

01:21:47.220 --> 01:21:51.470
One is processing stimuli
with high pitch salience,

01:21:51.470 --> 01:21:54.170
and the other is
processing sound stimuli

01:21:54.170 --> 01:21:55.580
that change in location.

01:21:56.770 --> 01:22:00.180
So those are the two things you
can really hang your hat on,

01:22:00.180 --> 01:22:05.220
and what is done at the auditory
cortex in terms of function.

01:22:06.350 --> 01:22:08.625
And for the pitch
sensitive area,

01:22:08.625 --> 01:22:10.790
you have this area near A1.

01:22:12.760 --> 01:22:18.700
For the localization, you
have A1, posterior field,

01:22:18.700 --> 01:22:22.180
and a field near the
anterior ectosylvian sulcus,

01:22:22.180 --> 01:22:23.375
as we know currently.

01:22:27.280 --> 01:22:27.780
All right.

01:22:27.780 --> 01:22:28.279
Questions?

01:22:30.730 --> 01:22:32.735
If not, have a
good Thanksgiving.

01:22:33.850 --> 01:22:37.610
Don't eat too much, or enjoy
eating too much, I guess.

01:22:39.120 --> 01:22:41.410
I'll see you on Monday.