Lecture Six; Brain Machine Interface

Question 1

What was the first study of neural movement?

Answer 1

Fritsch

First idea that;

• Motor cortex was responsible for motor control
• Areas of the cortex are connected to specific muscles

Question 2

What did fritsch do?

Answer 2

• Very first electrical recording generating a MAP

- Used observation

Question 3

What did penfield study do?

Answer 3

Drew the motor homonculus

Note; functions are not perfectly delineated i.e there are areas of overlap that encode for movement

Question 4

What is the evarts study?

Answer 4

Relation of pyramidal tract activity to force exerted during voluntary movement

Question 5

Describe the setup for the evarts study;

Answer 5

• AWAKE Monkey with stimulating electrode in the pyramidal tract
• Recording electrode in wrist area of right motor cortex
• Wrist flexion / extension, with and without load atnagonist

Question 6

What was recorded in the evarts study as the monkey performed the wrist movements?

Answer 6

• Recording SINGLE neurons in the motor cortex.

Confirm these are PTNs by stimulating the spinal cord

Question 7

In the evarts study what movement did the monkeys perform?

Answer 7

Extension to flexion movement

Question 8

Describe the neural recordings in the evarts study, no load, extension -> flexion ;

1/3

Answer 8

• Extensors tonically active, holding it in extension (when move to flexion, little activity present)
• Move to flexion, burst of activity then tonic
• CTN active with agonist muscle

look at page 20

Question 9

Describe the neural recordings in the evarts study, FLEXOR load, extension -> flexion ;

2/3

Answer 9

• Burst of flexor activity following movement, then tonic
• No extensor activity
• CTN (corticopsinal tract neurons) activity increases with increased load

Question 10

Describe the neural recordings in the evarts study, EXTENSOR load, extension -> flexion ;

3/3

Answer 10

• Extensor burst prior to movement

- no CTN activity, flexion movement results from relaxation of agonist

Question 11

What was the conclusion of the evarts study;

Answer 11

• Single cell firing encodes for contraction
• “neurons behave like muscles”
  i. e direction + muscle contraction all in same direction therefore if neurons encoded direction then activity would be the same for all movements (doesnt happen in this study)

THis is old and not true in reality

Question 12

Describe the setup for the georgopoulus study 1982;

Answer 12

• The activity of SINGLE CELLS in the motor cortex were recorded while monkeys made movements in 8 directions (45 degree intervals) in a 2d apparatus.
• Same start point
• Same amplitude of movement

Question 13

In the georgopololus study, how many neurons were able to be examined?

Answer 13

• The frequency discharge of 241/323 cells (74.6%) varied in an orderly fashion with the direction of movement

Question 14

In the georgopolus study when was neuron discharge rate the highest?

Answer 14

Discharge was most intense with movements in a preferred direction

and was reduced gradually when the movement was made farther and farther away from the preferred direction

Question 15

What graph did the georgeopolus researchers create?

Answer 15

Resulted in a bell shaped directional tuning curve

Question 16

Describe the relationship of the directionally tuned cells;

Answer 16

75% of the 241 directionally tuned cells, the frequency of discharge, D, was a sinusoidal function of the direction of movement.

Firing rate = baseline + m (modulation) cos (movement direction (angle) - Preferred direction (angle))

Question 17

What did they find with tuning curves and the neuron population?

Answer 17

Preferred directions differed for different cells so that the tuning curves partially overlapped

Question 18

What was the georgeopolus conclusion / hypothesis?

Answer 18

Movement trajectory in a desired direction might be generated by the cooperation of cells with overlapping tuning curves

‘Population coding’

Question 19

Describe the schwartz 1988 study;

Answer 19

• Awake monkeys, single neuron recording, 8 3D directions of movements
• Equal amplitude of movement
• Same starting position

Question 20

What was schwartz 1988 describing?

Answer 20

The relationship between the neuronal activity in primate motor cortex and the direction of arm movement in 3D space.

Question 21

What was found in the schwartz study?

Answer 21

• Discharge rate of cells varied in an orderly fashion with the direction of movement i.e neurons have a preferred 3D direction of movement (highest discharge)

Question 22

What was the conclusion of the schwartz 1988 study?

Answer 22

Preferred directions are uniformly distributed in space i.e all directions are equally represented (populations of neurons)

Question 23

What formula did the schwartz 1988 study create?

Answer 23

Firing rate = baseline + Bx Dx + By Dy + Bz Dz

Bx = Preferred direction, x plane
Dx = Direction, x plane

(vector representation)

Question 24

What did the georgopolus + schwartz 1988 study describe?

Answer 24

A code by which a population of motor cortical neurons could determine uniquely the direction of reaching movements in 3D space.

Question 25

What did the georgopolus + schwartz 1988 study find?

Answer 25

The neuronal population code (cosine tuning) assumes that for a particular movement direction each cell makes a vectorial contribution (votes) which direction in the cells preferred direction and magnitude proportional to the change in cells discharge rate associated with the particular direction of movement

Question 26

What do these vectors contribute to?

Answer 26

The vector sum of these contributions is the outcome of the population code (population vector algorithm) and points in the direction of movement in space well before the movement begins

Question 27

What was the conclusions of the georgopolus + schwartz 1988 study about population size and confidence?

Answer 27

Confidence cone,

Describes the confidence for the number of neurons in the population vector as to how accurate it will be

<50 = best

Question 28

Describe the kakei study;

Answer 28

The activity of motor neurons (m1) was recorded in monkeys trained to perform a task that dissociates three major variables of wrist movement; muscle activity, direction of movement at the wrist joint, and direction of movement in space.

i.e trying to determine what exactly is represented in M1, muscle action of direction

Question 29

What were the findings of the kakei study?

Answer 29

• 28/88 neurons displayed changes in activity that were muscle like
• 44/88 displayed changes in activity that were related to the direction of wrist movement in space independant of the pattern of muscle activity that generated the movement.

Thus both muscles and movement appear strongly in M1

Question 30

Describe the kakei results;

Answer 30

• Muscles will shift their direction of movement preference based on hand orientation (pronation vs mid vs supination)
• Neurons dont change their direction preference regardless of hand orientation
• Neurons increase their rate of firing with changes in hand orientation (gain modulation, muscles more or less activated to perform the movement based on ahdn orientation)

Neurons behave like muscles

Question 31

What was the schwartz 7.5 study set up?

Answer 31

Illusion where monkeys saw they were drawing ellipses but over time the computer software altered the algorithm so that they were actually drawing circles but they saw ellipses.

Illusion

Question 32

What did schwartz 7.5 study find?

Answer 32

Pre-motor cortex encoded ellipses,

M1 had smaller signals (visumotor transformation??)

Question 33

Describe the churchland study set up;

Answer 33

Monkeys performed tasks at varying speeds while neuron recordings were taken

Question 34

What did the churchland study find?

Answer 34

Neurons may encode velocity

Tuning for direction was prominent but the preferred direction was inconsistent with respect to time, instructed speed, and or reach distance

Question 35

What two theories was the churchland study deliberating?

Answer 35

Dynamic system vs representative

Question 36

Describe churchlands dynamic system;

Answer 36

• Individual neurons may not represent anything
• Instead their activity is whatever is needed to generate the correct movement
• Neural networks show complexity

Question 37

What is a dynamical system?

Answer 37

A dynamic system whose state evolves with time according to a fixed rule

Where you start determines where you end up

Question 38

What was the shenoy study?

Answer 38

Reviews premotor cortex function in the dynamical systems view

Question 39

What did the shenoy study conclude?

Answer 39

Where in the neural space you start the trial after the prepatory period determines the path you take and where you end up

i.e where you start in the prepatory period determines everything, dynamic system