Cerebellum Flashcards
What did Marr propose?
A detailed theory of cerebellar cortex was proposed by Marr in 1969 to outline how the cerebellum may learn to perform motor skills. He describes two forms of input-output relation, both consistent with the cortical theory. One is suitable for learning movements (actions), and the other for learning to maintain posture and balance (maintenance reflexes).
What was Marr’s theory based off of?
cells of the inferior olive and the cerebellar Purkinje cells have a special one-to-one relationship induced by the climbing fibre input
What are the assumptions made for learning actions?
a. each olivary cell responds to a cerebral instruction for an elemental movement. Any action has a defining representation in terms of elemental movements, and this representation has a neural expression as a sequence of firing patterns in the inferior olive; and
b. in the correct state of the nervous system, a Purkinje cell can initiate the elemental movement to which its corresponding olivary cell responds.
What happens when an olivary cell fires?
it sends an impulse (via the climbing fibre input) to its corresponding Purkinje cell
What is the Purkinje cell exposed to?
(via the mossy fibre input) to information about the context in which its olivary cell fired; and it is shown how, during rehearsal of an action, each Purkinje cell can learn to recognize such contexts. Later, when the action has been learnt, occurrence of the context alone is enough to fire the Purkinje cell, which then causes the next elemental movement. The action thus progresses as it did during rehearsal.
Can Purkinje cells learn more than one context?
each Purkinje cell can learn a number of contexts
What is the exposure of different contexts to Purkinje cells consistent with?
consistent both with the distributions of the various types of cell, and with their known excitatory or inhibitory natures.
What provides pattern discrimination in Purkinje cells?
It is demonstrated that the mossy fibre-granule cell arrangement provides the required pattern discrimination capability.
What 3 predictions are made about action movement in the cerebellum?
(a) The synapses from parallel fibres to Purkinje cells are facilitated by the conjunction of presynaptic and climbing fibre (or post-synaptic) activity.
(b) No other cerebellar synapses are modifiable.
(c) Golgi cells are driven by the greater of the inputs from their upper and lower dendritic fields.
In what way is the cerebellar circuit for learning maintenance reflexes compared to actions?
Each olivary cell is stimulated by one or more receptors, all of whose activities are usually reduced by the results of stimulating the corresponding Purkinje cell.
What is considered the stabilizing reflex circuit for maintenance reflex?
the circuit receptor → olivary cell → Purkinje cell → effector
What is the stabilizing reflex circuit activated by?
Learned mossy fibre inputs
What is the maintenance reflex also called and what can this reflex do?
This type of reflex has been called a learned conditional reflex, and it can solve problems of maintaining posture and balance.
