Biopsych Lecture 7

Front 1

Reaching task: describe setup and results

Back 1

Motor reaching task with handle and targets, also performed by monkeys

Found:
Speed profiles smooth
BUT
Joint movement and musculoskeletal apparatus are COMPLEX: might have to reverse/switch force, direction

Front 2

Dynamics problem

Back 2

How do you convert muscle activity into appropriate joint torques with appropriate timing

Front 3

Extrinsic kinematics

Back 3

High level features a motor plan

Identifies target location
Pictures spatial hand paths

Front 4

Intrinsic Kinematics

Back 4

Figures out what the JOINT MOTIONS are

Front 5

Intrinsic dynamics

Back 5

Figures out joint torques and muscle activity

Front 6

M1/cortex does which part of the plan?

Back 6

Extrinsic kinematics, only makes a motor plan - not the actual dynamics problem

Front 7

What parts (may) solve the dynamics problem?

Back 7

The brain stem and spinal cord

Front 8

How can we find the parts of the brain that solve the dynamics problem?

what is one thing (example) you might measure from?

Back 8

Record neural activity in individual neurons across brain, assess their activity profiles

Use fMRI and PET

EXAMPLE: put electrode in large pyramidal betz cell in cortex which sends output to cortical spinal tract while monkey does reaching task

Front 9

Preferred direction

Back 9

Discharge pattern for each neuron is related to direction. So, each neuron is specialized for one direction, called the preferred direction

Front 10

Neuronal firing rate can be represented as...

Back 10

a vector, which shows overall direction and strength towards that direction for each neuron

NOTE: Firing rate also varies with FORCE - more force = stronger vector

Front 11

Population vector

Back 11

The overall vector/summation over a population of neurons

Front 12

All directions have..

Back 12

a population vector

Front 13

If you train the monkey to rotate the vector 90 deg from what is actually shown...

Back 13

you can see the anticipation in the neurons through the "flipping" of vectors - the overall population vector turns 90 deg.

This is called DIRECTIONAL DISCHARGE PATTERN

Front 14

Directional discharge pattern is also used in

Back 14

3 dimensions

Front 15

Vector hypothesis

Back 15

explains how the mind deals with the extrinsic kinematics issue - planning/visualizing movement - BUT NOT the dynamics problem

Front 16

fMRI activation during directional movement in humans shows..

Back 16

the motor cortex is one of several areas in brain activated

Front 17

Properties of population vector coding scheme for movement

Back 17

1) Predicts movement direction for different origins
2) Different cortical layers contribute similarly
3) Does not depend on single cell
4) Predicts the direction of the force

Front 18

Other possible solutions to the dynamics problem (that don't work)

Back 18

Table lookup method- every movement is a little varied, doesn't work

Compute in real time - too long

so neither works

Front 19

Equilibrium hypothesis

Back 19

A set position can be achieved by a balance in agonist and antagonist muscles

Front 20

Solution to dynamics problem

Back 20

Microstimulation of spinal cords reveal modules of equilibrium points

Sequential activation of these modules can produce movement

A sequence of equilibrium points could move limbs in consistent pattern

Higher level (supraspinal) systems could play the keys in this modular system to invoke particular movements

Modular organization of spinal cord - provides an alphabet of equilibrium points

Front 21

Notes about neural coding/representation of behavior in brain

Back 21

No single neuron has the code for a movement, coding is a distributed process across many brain structures and layered heirarchial systems

Front 22

Shorcomings of vector hypothesis

Back 22

Directional coding not adequate since some neurons are clearly related to forces - not direction

Other neurons related to accelaration, movement preparation, arm position, etc...

too many codes not well explained

Front 23

Exploiting vector hypothesis

Back 23

Using utah electrode array on cortex, measure 100 neurons simultaneously to see animal's intention (what does it WANT to do), use brain-machine interface (with monkey)

Front 24

Which disorder's patients have a hard time with movement sequences?

Back 24

Parkinsons

Reaction and movement times slower, even though they can LEARN complex tasks

performance of well learned motor plans impaired

Front 25

What brain part is responsible for automatic execution of motor movement?

Back 25

basal ganglia

Front 26

Motor plan

Back 26

1) Concept about neural processing
2) Between perceptual recognition and motor action
3) Concept of action
4) Requires sequential motor action

Front 27

What is an example of a syntatic chain? Describe it

Back 27

Rodent grooming

INNATE Movements in chain sequences
Depends on integrity of striatum
INDEPENDENT of learning/memory
Some movements in flexible combinations
nonchain grooming unchanged by striatal lesions