Lecture 14: The Neurobiology of Motor Control

Question 1

What is the anatomy of motor control?

Answer 1

Motor control, the ability to regulate movement, involves a complex interplay of brain regions, including the motor cortex, basal ganglia, cerebellum, and spinal cord, working together to plan, execute, and refine movements

Question 2

What is the function of the spinal cord?

Answer 2

Provides direct control of the muscles via motor neurons and interneurons.

Question 3

What is the length of axons in a motor neuron?

Answer 3

Up to a metre in length

Question 4

What is the function of the preomotor/SMA and parietal cortex?

Answer 4

Action plans and goals

Question 5

What is the function of the primary motor cortex and subcortical brain region?

Answer 5

Translate the motor plans and goals into specific actions

Question 6

What are muscles composed of?

Answer 6

Elastic fibres that can change in length and tension

Question 7

How are muscles arranged?

Answer 7

In antagonist pairs e.g. biceps and triceps

Question 8

What is motor control carried out by?

Answer 8

Muscles, so when the biceps contracts, the triceps relaxes which enables flexion of the elbow, and if the triceps contracts and the biceps contracts this enables extension of the elbow.

Question 9

What are muscles controlled by?

Answer 9

Motor neurons in the spinal cord

Question 10

Where do motor neurons originate?

Answer 10

In the spinal cord and exit through the ventral root and terminate in the muscle fibres

Question 11

What does action potential in the motor neuron trigger?

Answer 11

The release of acetylcholine - a neurotransmitter that makes muscle fibres contract

Question 12

What determines the force that the muscles can generate?

Answer 12

The number and frequency of action potential and number of muscle fibres

Question 13

How many cranial nerves control essential reflexes which keep us alive?

Answer 13

12

Question 14

What to extrapyramidal tracts?

Answer 14

Send direct pathways down the spinal cord to exert indirect control over posture, muscle tone and movement speed

Question 15

What does the motor cortex regulate?

Answer 15

Activity of spinal motor neurons

Question 16

What is the function of corticospinal (pyramidal tract)?

Answer 16

Has axons that project directly form the cortex to the spinal cord

Question 17

Where do the cerebral hemispheres control movement?

Answer 17

On the opposite side of the body

Question 18

What are somatotopic organisations?

Answer 18

Different regions represent different body parts. The representation looks something like this, with larger areas dedicated to parts of the body involved in movement such as the hands and face.

Can elicit predictable twitches in the different regions using TMS

Question 19

What are the premotor and SMA involved in?

Answer 19

Planning and the control of movement, either sensory guided or internally guided.

Question 20

What do lesions result in?

Answer 20

Apraxia, which affects movement of limbs and also speech

Question 21

What is the association motor areas involved in?

Answer 21

Representation of space, attention, sensorimotor integration

Question 22

What do lesions of parietal cortex produce?

Answer 22

Apraxia but also more general problems with attention, particularly spatial attention (nelgect)

Question 23

What are Central Pattern Generators (CPGs)?

Answer 23

Neurons in the spinal cord that can generate rhythmic, patterned movements required for complex motor acts without input from higher brain regions.

Question 24

What experiment did Sherrington conduct to study motor control?

Answer 24

He severed the spinal cord of cats and placed them on a treadmill, observing that they could still produce rhythmic limb movements for walking.

Question 25

What did Sherrington’s experiment reveal about CPGs?

Answer 25

Even without descending commands from the brain, the spinal cord could independently generate rhythmic movements, proving the existence of CPGs.

Question 26

How do CPGs contribute to the hierarchical nature of motor control?

Answer 26

Higher-level brain regions can send simple signals to trigger CPGs instead of holding the entire representation of complex movements themselves.

Question 27

What did Georgopoulos' experiment investigate?

Answer 27

How neurons represent the direction of movement in the brain.

Question 28

What task did Georgopoulos require monkeys to perform?

Answer 28

Move a lever from a center position to one of eight targets.

Question 29

What was the key finding from Georgopoulos' experiment?

Answer 29

Neurons showed a preference for a specific movement direction, regardless of the starting position or target location.

Question 30

What does Georgopoulos' experiment suggest about motor control?

Answer 30

The brain encodes movement direction rather than absolute position, indicating a more abstract representation of movement.

Question 31

What is the concept of a population vector in motor control?

Answer 31

A population vector is the sum of individual neuron vectors, which helps predict the direction of movement.

Question 32

How does a single neuron's preferred direction contribute to movement prediction?

Answer 32

Each neuron has a preferred direction, but since neurons respond to multiple directions, a single neuron is not enough to predict movement accurately.

Question 33

How does the population vector improve movement prediction?

Answer 33

By summing the vectors of multiple neurons, the population vector provides an accurate prediction of movement direction, even 300 ms before movement initiation.

Question 34

How is the concept of population vectors used in brain-machine interfaces?

Answer 34

Population vector output is used to predict movement direction, forming the basis for brain-machine interfaces.

Question 35

What pioneering experiment did Chapin conduct on brain-machine interfaces?

Answer 35

He trained rats to press a lever for a reward while recording multiple neuron responses in the motor cortex.

Question 36

How were neural networks used in Chapin’s experiment?

Answer 36

They learned patterns of neuronal activation to predict the forces exerted on the lever.

Question 37

What was observed in the population vector responses in Chapin’s experiment?

Answer 37

The output of around 40 neurons showed complex patterns of activation during different stages of lever pressing.

Question 38

What does the population vector response reveal about motor control?

Answer 38

It shows how groups of neurons coordinate to generate movement and how their combined activity can predict force and direction.

Question 39

How did Chapin modify the experiment to test brain-machine interface learning?

Answer 39

He switched the input to the reward system from the lever to the neuronal population vector.

Question 40

What happened when the reward was no longer linked to the lever press?

Answer 40

Mice stopped pressing the lever as they learned the force exerted was no longer correlated with the reward.

Question 41

What surprising behavior did the mice exhibit after the switch?

Answer 41

They continued generating the cortical signals necessary to move the lever, even without physical movement.

Question 42

How can adaptation to sensorimotor mismatches be studied in the lab?

Answer 42

Using the "hidden hand" paradigm, where a mismatch is created between actual hand movement and perceived movement, leading to adaptation over time.

Question 43

What happens in the brain during the adaptation phase?

Answer 43

Increased activation across many different motor regions.

Question 44

How do lesions in motor areas affect visuomotor adaptation?

Answer 44

Patients with lesions in motor control areas show deficits in visuomotor adaptation, suggesting these regions are critical for the process.

Question 45

What method did Galea et al. use to investigate visuomotor adaptation?

Answer 45

Transcranial direct current stimulation (tDCS), which applies electrical currents to the scalp to change neuronal excitability.

Question 46

What was the effect of tDCS on the cerebellum in Galea et al.'s study?

Answer 46

It led to a faster rate of adaptation.

Question 47

What was the effect of tDCS on the primary motor cortex (M1) in Galea et al.'s study?

Answer 47

It led to increased retention of adaptation, causing more error for a longer period after adaptation ended.

Question 48

What role does the cerebellum play in visuomotor adaptation?

Answer 48

It is involved in learning new movement mappings, possibly by generating forward models.

Question 49

What role does M1 play in visuomotor adaptation?

Answer 49

It consolidates newly learned mappings, playing a less flexible, instructive role by passing motor plans to spinal cord motor neurons.

Question 50

What experiment did Miall and colleagues conduct to investigate the cerebellum's role in forward models?

Answer 50

They had subjects move their arm to the right, then make a movement to a visual target after hearing a tone, requiring a prediction of where the hand would be due to a delay between the tone and the movement initiation.

Question 51

Why is a prediction of the hand's location necessary in Miall and colleagues' experiment?

Answer 51

Because there is a delay between hearing the tone and initiating the movement, and without a prediction, the motor command would be out of date, causing the subject to miss the target.

Question 52

What did Miall and colleagues find under normal conditions in their experiment?

Answer 52

Subjects were generally accurate in hitting the target, suggesting they were predicting the hand's future location.

Question 53

What happened when TMS (Transcranial Magnetic Stimulation) was applied in Miall and colleagues' experiment?

Answer 53

The path of the hand matched what would have been expected if the motor command had been issued 138 ms earlier than when the movement was initiated.

Question 54

What does the finding from Miall and colleagues’ experiment suggest about the cerebellum?

Answer 54

It suggests that the cerebellum plays a crucial role in generating forward models by predicting the future location of the hand and adjusting the motor command accordingly.