Course Overview

Introduction

Issue 1: What is Controlled?

• Striated muscles (n=640)
• Tendons
• Bones
• Joints
• Soft tissue
• + Smooth muscles
• + Glands

Distinction Between Voluntary and Involuntary Movements:

• Reflexes
• Example: patellar reflex (myotatic reflex)
• Is a knee jerk not voluntary?
• Modulation of reflexes
• Jendrassik maneuver
• Suppression of reflexes

External:

• Visual
• Auditory

Issue 2: Cues Used by the Nervous System

• Reflexes
• Example: patellar reflex (myotatic reflex)
• Is a knee jerk not voluntary?
• Modulation of reflexes
• Jendrassik maneuver
• Suppression of reflexes

External:

• Visual
• Auditory
• Touch/Pressure
• Pain
• Gravity
• Receptors
• Olfactory

Internal:

• Proprioreceptors
• Receptors in muscles, tendons, fascia and ligaments
• Learned triggers
• S    R
• UCS    UCR
• (Si + UCS)n    Si    Ri
• Intention
• Cognitive Control

Issue 3: Cues Used by the Nervous System to Control Movements

• Sensorimotor, mnemonic, and cognitive
• Example of the language system

Issue 4: Levels of Analysis

Level I:

• Emotion/Cognition
• Grapho-Motor System
• Motor-Speech System
• Auditory System
• Visual System
• Writing Speaking Hearing Reading
• Formulation

Language System:

• Working
• Memory
• Comprehension
• Serial model of motor control
• Computations required by serial model of motor control
• Feed-forward / feedback control

Issue 5: What is Computed and How?

Serial Model of Motor Control:

• Definitions

Kinematics:

• Change in position, for example, of limb over time. Could specify in terms of timedependent changes in joint angle.

Dynamics:

• Patterns of forces associated with the movements – joint torques.
• Assume you visually specify object position with respect to the body. To reach it, is then necessary to compute:
  • Inverse kinematics: Compute the joint angle to get the finger to the target.
  • Inverse dynamics: Given desired target position and kinematics, compute the forces needed to get the arm there.
• Computations required by serial model of motor control
• Feed-forward / feedback control
• E.g. touch X
• Eye in head
• Head on trunk
• Arm on trunk
• Arm joints / hand
• Egocentric
• Center scan
• Retinotopic
• Object centered?

Issue 6: Spatial Coordinate Frames Used for Sensorimotor Control

• Cerebral cortex
• Basal ganglia
• Cerebellum
• Brainstem
• Spinal cord

Issue 7: What Brain Regions are Involved in Motor Control?

• Stimulation
• Ablation / human clinicopath correlations
• Anatomy of connections
• Animal studies
• Reflexes
• Locomotion
• Behavioral patterns
• Gene-based studies

Issue 8: What Techniques are Used to Study Motor Control?

• Degrees of freedom problem
• Serial order of behavior
• Sensory / perceptual motor transform
• Motor equivalence
• Motor learning and plasticity
• Higher order control: cognition, motivation
• Computational models

Issue 9: Challenges for the Field

• 3DF

Degrees of Freedom Problem:

• 1DF
• DF
• DF 3DF at wrist
• 2DF

Degrees of Freedom Problem:

1. Plan ahead
2. Minimize jerk (da/dt)
3. Built-in synchronies (e.g. “associated movements”)
4. “Too complicated so can’t be done so we don’t do it” (Alexander + Crutcher)
5. End point calculations vs. trajectory calculations

Possible Solutions to the Degrees of Freedom Problem:

• Speech
• Complex actions
• Milk in cupboard
• Cereal box in fridge
• Co-articulation
• Fingers move ahead – not in order of letters to be typed – as in “an epic”
• Modularity?
• Chunking?

Examples of Serial Order of Behavior:

• Source: Rosenbaum, D.A. (1991) Human Motor Control. New York, Academic, p. 16.

Co-articulation

• Source: Rosenbaum, D.A. (1991) Human Motor Control. New York, Academic, p. 6.
  

Sample Lecture Outline for Lecture 5: Motor Cortex

Primary Motor Cortex

• M1 has body map
• But controversy about maps is coming...
• Wilder Penfield experiments
• Microelectrode stimulation-recording experiments (Asanuma)
• Multiple motor areas in addition to M1

Role of the Pyramidal Track

• Anatomy of the Pyramidal Track (origin and destination)
• Stroke
• Privileged access to motor neurons in spinal cord
• Kuypers' experiments (transsection of pyramidal tract vs.. reticular spinal tracts)
• Paradox of one PT neuron innervates motor neurons for multiple motor neuronal pools

What is Coded by M1 Neurons?

• Breakthrough with experimental protocol introduced by Edward Everets (1960's)
• M1 neurons code for load - early story
• M1 neurons have a population code for direction of movement (Georgopoulos experiments)
• Population vectors

M1 Map/Representation is Highly Plastic.

• Laboratory evidence (Nudo)
• Evidence from human scans

What M1 Neurons Respond to is not Simply Related to Corresponding Muscle EMG Activity.

• Different conditions producing EMG activity in a single muscle may not all induce spike activity in a motor neuron connected to that muscle.

The Hypothesis that Different Motor Cortical Areas Specialize in Different Aspects of Movement.

• "Simple" movements
• Sequential movements
• Imagined movements