Function of the Cerebellum/Basal Ganglia Flashcards Preview

Nervous System: Unit III > Function of the Cerebellum/Basal Ganglia > Flashcards

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Characteristics of a feeback controller

  • 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.  


Characteristics of a feedforward controller

  • 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


Feedback vs. Feedforward in motor control

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


Parietal cortex role in reaching motion

  • 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.


Processing of visual info 

  • 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.  


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


  • 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


Mossy fiber role in cerebral-cerebellar coordination

  • 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


Ventral tegmentum (VTA) characteristics

  • 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.



Activity of dopaminergic neurons during reward trials

  • 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.


Mechanism of VTA/SNc reward prediction


  • 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.