Motor control

Question 1

What are corticospinal tracts?

Answer 1

Direct pathways from the motor cortex to the lower motor neurones.

Question 2

Describe a typical corticospinal tract.

Answer 2

Mono synaptic connection to increase speed.
Neurons in the motor cortex give rise to axons that travel through the internal capsule to the ventral surface of the midbrain.
These axons continue through the pons and come to lie on the ventral surface of the medulla, giving rise to the pyramids.
Most of these pyramidal fibres cross in the caudal part of the medulla to form the lateral corticospinal tract in the spinal cord.

Question 3

What are the functionally distinct motor areas?

Answer 3

Supplementary motor area / cortex (SMA)
Primary motor area / cortex (M1)
Posterior parietal area / cortex
Premotor cortex (PMA)

Question 4

What are the descending pathways responsible for?

Answer 4

planning, initation, execution and direction of voluntary movements.

Question 5

What is the Graziano M. 2006 study?

Answer 5

Long (meaningful) stimulation of primary motor areas (M1) caused natural movements in monkeys. Discovered that M1 causes simple as well as complex muscle movements.

Question 6

What is the directional tuning experiment?

Answer 6

1. Monkey in restrained chair with electrode implant.
2. Operantly conditioned to move joystick in response to light.
3. Raster plot used to illustrate firings of individual neurones.
4. Certain neurones only fired in response to certain angles of the monkey’s movement. A preferred range.
5. Each upper motor neurone has a preferred direction. This is determined by which neurones fired most in response to a movement direction.

Question 7

Which area of the brain is responsible for defensive behaviour?

Answer 7

Premotor area (PMA). Electrical stimulation of the PMA caused defensive behaviour in primates.

Question 8

What areas do complex motor tasks activate?

Answer 8

M1 and SMA. Mostly SMA. Simple motor tasks do not engage the SMA.

Question 9

Where and how in the brain do we store information for the orderly performance of volitional movements?

Answer 9

Tanji and Shima (1994) found a group of cells in the SMA in the cerebral cortex of monkeys who’s activity is exclusively related to a sequence of multiple movements performed in a particular order.

Question 10

What was the previous idea about motor control areas of the brain?

Answer 10

A topographic map of the cortex shows how each area of the cortex has a specific body part it is responsible for. These areas of the cortex can be divided into the corticospinal tract area and corticobulbar tract area. This idea has since been disproved.

Question 11

Describe Tanji and Shima’s 1994 study.

Answer 11

A monkey was trained to do a set of movements in a certain order, (pushing, pulling or turning the joy stick). Discovered that neurones fire in anticipation of a movement, but go silent during the actual action of a movement. Certain neurones only responded in response to a certain order of movements. They aren’t responsible for the actual action but order. Pre SMA neurones only and always fired before the 3rd movement, regardless of what the movements were.
Also, certain neurones in M1 fired only in response to certain movements (push) and were not affected by order or anything like that.

Question 12

What is the crayfish startle response?

Answer 12

involving lateral and medial giant neuronal fibres to excite flexor motor neurones via electrical synapses. Fast and involuntary reflex reaction.

Question 13

What is the desophila giant fibre system?

Answer 13

Giant neurones in giant fibres synapse onto motor neurones via electrical synapses. Used in escape flight which is characterised by a jump to initiate flight without wing use and chaotic initial orientation. Makes the flight path unpredictable.

Question 14

What are the 3 levels of motor control?

Answer 14

Level 1 - spinal cord, muscles, motor neurones
Level 2 - brainstem - improve postural control, vary speed of oscillatory patterns.
Level 3 - cerebral cortex

Question 15

What was Benjamin Libet’s experiment? (1983)

Answer 15

Unconscious initiation of of a freely voluntary act. Readiness potential proposed by him. Brain activity recorded while the participant was able to press a button whenever he felt like it. Had to remember the time when they decided to press the button. Brain started to prepare for the action before conscious decision made (about 1.5 second build up of potential before action).
Suggests there is an unconscious path underlying experience of conscious will. The actual causal path is not present in our unconsciousness.

Question 16

What is the fMRI evidence of Libet’s experiment?

Answer 16

Participant had to remember what card was being displayed when they decided to press a button. Right and left motor cortex as well as pre supplementary area displayed activity AFTER conscious decision was made. However
Lateral and medial frontopolar cortices displayed heightened activity BEFORE the decision was consciously made.

Question 17

What are mirror neurones?

Answer 17

Discovered first in monkeys
Neurones that discharge both when the monkey executes a motor act as well as when it observes another individual carrying out the act. They don’t discharge with presentation of food or other interesting objects, or when observing hand actions mimicked without the target object.
Found in the inferior parietal lobe

Question 18

Where are mirror neurones found?

Answer 18

Parietal lobe (P5)
Frontal lobe (F5)

Question 19

What is the function of the parietal lobe?

Answer 19

Integrating sensory information from various parts of the body and in the manipulation of objects.

Question 20

What are the three steps to conscious decisions?

Answer 20

1. Deliberation/prior intention in the frontopolar cortex
2. The preparation of the action in the supplementary motor area. Generates readiness potential
3. Immediately before action, M1 is active.
   Then the neural signals leave M1 down spinal cord converging on lower motor neurones.

Question 21

What are the binding processes?

Answer 21

Prediction - during a decision, predictions are made on the action and the outcome of the action
Reconstructive inference - After the action, retrospectively assesses the importance of the intention and action.
They bind the 3 aspects of conscious experience together (intention action and outcome).

Question 22

What are the 5 cognitive processes underlying the experience of voluntary action?

Answer 22

1. Self as agent
2. Sense of voluntary control
3. Binding processes
4. Conscious experience
5. Neural events

Question 23

What is the experimental evidence that mirror neurones understand the ‘what’ and the ‘why’ of an action?

Answer 23

The neurones fired when watching an action with the object as well as after when the object was hidden but the action was the same. Mirror neurones seem to have some understanding of the observed actions.

Question 24

What is the cerebellum responsible for?

Answer 24

coordinated execution of movements, maintenance of balance, motor learning.
Number of fibres entering cerebellum much higher than what leaves (a ratio of about 40:1 - CONVERGENCE)
Must ensure that behaviour is appropriate for task

Question 25

What type of circuit is the cerebellum a part of?

Answer 25

A closed side loop

Question 26

From where does sensory information go to the cerebellum?

Answer 26

skin, joints, muscles, vestibular apparatus, eyes.

Huge amounts of the cerebral cortex project to the cerebellum.

Question 27

Describe the output circuits of the cerebellum.

Answer 27

Ascending 
- projections from cerebellum to cortex
- brainstem
Descending
- Brainstem eg Vestibular nuclei.

Question 28

Summarise the motor modulation of the cerebellum.

Answer 28

1.The central processing
component, the cerebellar cortex,
receives massive input from the
cerebral cortex and generates
signals that adjust the responses
of upper motor neurones to
regulate the course of a
movement.
2.Modulatory inputs also influence
the processing of information
within the cerebellar cortex.
3. The output signals from the
cerebellar cortex are relayed to the
thalamus and then back to the
motor cortex, where they
modulate the motor commands.

Question 29

Describe pathological changes to cerebellum after alcohol abuse.

Answer 29

degeneration of anterior cerebellum. Caused difficulty in walking

Question 30

Examples of effects of lesions to the cerebellum

Answer 30

Ataxia - disturbances in voluntary movement coordination
- dysmetria
- Asynergia
Flocculomodular syndrome - disturbances to eye movements

Question 31

What is the vestibulo - occular reflex?

Answer 31

keeping your eyes directed towards the same point in space as your head moves.

Question 32

What are the adaptive changes in the vestibulo - occular reflex?

Answer 32

When animal wears minifying glasses, the eyes move too far with respect to the slippage of the visual image of the retina.
After some practise, the VOR is reset so the eyes move a shorter distance in relation to head movement.

Question 33

Describe cerebellar structures in VOR.

Answer 33

One climbing fibre from the inferior olive synapses onto each purkinje cell but with many synapses (divergence). Many mossy fibres become parallel fibres and synapse onto one purkinje cell however many dendrites of the purkinje cell (convergence).
1. Both the mossy/ parallel fibres and climbing fibres provide excitatory inputs to purkinje cells as well deep nuclear cells. This is important. Why?
Allows error correction signal to be generated, as if level of excitation at deep nuclear cells is different to excitation at site of purkinje cell divergence, then it can detect an error.
Error corrected by GABAergic (-) connection between purkinje and deep nuclear cell. ALSO, error corrected via: The climbing fibres modify the efficacy of the parallel fibre to Purkinje cell connection, producing long-term changes in cerebellar output (e.g., LTD).

Question 34

Describe the cellular mechanisms of the adaptation of the vestibulo-ocular reflex (VOR). (The LTD changes).

Answer 34

1. the cerebellum recieves afferent information about head movement and retinal slippage.
2. The cerebellar flocculus detects mismatch between afferent information of head movement and retinal slippage. (If you buy new glasses)
3. Plastic changes occur due to coinciding climbing fibre and parallel fibre activity.
4. Purkinje output is modified. (error correction)
5. VOR gain is adjusted.
   This is all using excitatory inputs (glutamate) apart from the purkinjej output to the deep nuclear cell (gaba). They are inhibitory.