Function of the Cerebellum/Basal Ganglia

Question 1

Characteristics of a feeback controller

Answer 1

• e.g. a simple thermostat:
  
  • turns on a powerful heater when room temperature drops below a certain threshold
  • turns on a powerful cooling system when the temperature exceeds a certain threshold.
• This would describe a feedback- regulated thermostat.
• Though simple and accurate, feedback regulation tends to be slow and attempts to speed it up cause oscillations.

Question 2

Characteristics of a feedforward controller

Answer 2

• Feedforward controllers use cues to predict the future state of the system based on an internal model of the system
• E.g. feedforward thermostat:
  
  • sense variables such as when the window opens, how much it opened, the outside temperature ==>
  • predicts the change in room temperature ==> activates the heater preemptively, counteracting the coming temperature drop, and maintaining stable target value
    *

Question 3

Feedback vs. Feedforward in motor control

Answer 3

• If using feedback instead of feedforward to target something you get an oscillation or intention tremor.

Question 4

Parietal cortex role in reaching motion

Answer 4

• In the parietal association cortex, the brain integrates visual information about the target and somatosensory information about the limb position ==>
• integrated information is fed to the motor cortices in the frontal lobe to guide movement of the limb to the target.

Question 5

Processing of visual info

Answer 5

• Visual information is processed first in the occipital cortex ==> two streams of information.
• “what” pathway = processed in ventral cortical areas that advance from occipital to the inferior temporal lobes ==> object form info
• “where” pathway = other stream of information advances dorsally from occipital cortex into the parietal lobe ==> info about location in space of visual stimuli.

Question 6

Mechanism of cerebellar adaptation of cortical networks (visual coordinates vs. joint position)

Answer 6

• Inferior olivary nucles = comparator = compares expected state to observed state
  
  • expected state is conveyed by outputs from deep cerebellar nuclei (GABA-nergic)
  • observed state is conveyed by visual and proprioceptive feedback to ION (project to fxnl zones of cerebellum)
  • if feedback differs from expected state ==> error signal via climbing fibers ==> complex spikes @ purkinje cells ==> long term depression modifications

Question 7

Mossy fiber role in cerebral-cerebellar coordination

Answer 7

• mossy fibers = reflective of current state of parietal cortical mapping between visual and proprioceptive signals
• mossy fibers ==> granule cells == parallel fibers ==> purkinje cells ==> dentate nucleus ==> thalamus ==> motor/premotor cortex

Question 8

Ventral tegmentum (VTA) characteristics

Answer 8

• The ventral tegmentum area (VTA) is a group of neurons located close to the midline on the floor of the midbrain.
• The VTA is the origin of the dopaminergic cell bodies of the mesocorticolimbic dopamine system and is widely implicated in the drug and natural reward circuitry of the brain.
• It is important in cognition, motivation, drug addiction, intense emotions relating to love, and several psychiatric disorders.

Question 9

Activity of dopaminergic neurons during reward trials

Answer 9

• first trial ==> unexpected reward ==> spike in the number of action potentials produced by the dopaminergic neuron
• After a few trials ==> association of the symbol with the reward ==> spike of dopaminergic neuronal activity ==> now occurring at the time of the reward-anticipating cue.
• more trials ==> relationship between the cue and the reward is established and expected ==> dopamine release will cease altogether.

Question 10

Mechanism of VTA/SNc reward prediction

Answer 10

• Dpoamine is released by dopanergic neurons @ VTA/SNc when unexpected rewards are encountered
• Occures b/c VTA/SNc = ~ION @ cerebellum
• Additional inputs to the SNc/VTA convey information about the actual experience of reward, the SNc/VTA acts as a comparator activated by a mismatch between observed and expected rewards.
• An unpredicted reward will strongly activate these neurons, and the dopamine released into the striatum will alter the activity and the plasticity of corticostriatal networks ==>
  
  • networks that correctly predicted the error will be reinforced, and those that do not correctly predict the error will be diminished.