cc 5

Question 1

Evidence on sites of plasticity: TWO issues?

Answer 1

1. cerebellum vs. brainstem

2. cerebellar cortex vs. deep cerebellar nuclei.

Question 2

Brain stem argument

Answer 2

Both sides agree that lesions to anterior inteprositus nucleus stop CR
Disagree on the mechanism of this effect
One side claims evidence for plasticity
- Brain stem - PERFORMANCE deficit

interpositus nucleus excites red nucleus

1. learning in area X produces CR command
2. combines with tonic excitation to produce CR

Question 3

evidence for brainstem view weak

Answer 3

Removal of tonic excitation should affect UR but UR still present even when CR is not - Yeo et al 1987

Question 4

evidence against brainstem argument (lesions)

Answer 4

Lesion cerebellar cortex decrease CR amplitude increase UR amplitude - cannot be explained by simple tonic effect on motor neurons
Gruart ad Yeo 1995)

Question 5

Evidence against brainstem argument

- cortical inactivation

Answer 5

Krupa, Thompson and Thompson (1993)
muscimol in red nucleus - no CR. CR when it wears off.
Muscimol in interpositus= NO CR when worn off= no learning.

Conclusion: MAjor site of plasticity for rabbit NMR and eyeblink conditioning is within cerebellum

Question 6

cerebellar cortex vs deep cerebellar nuclei

- lesions

Answer 6

unilateral cortical lesions in the right place impair conditioning
bilateral lesions abolish them
necessary evidence but not sufficient

Question 7

cerebellar cortex vs deep nuclei

- cortical inactivation

Answer 7

CNQX reversibly blockes AMPA receptors (PF-PC synapses)
- no CR after learning
Attwell et al., 2001

BUT
- might not be acting on PF-PC
BUT Still in cortex.

Question 8

cerebellar cortex vs deep nuclei

- cortical electrophysiology

Answer 8

Jirenhed et al 2007
- reduction in firing of purkinje cells in HVI eyeblink area shown by electrophysiological recordings.

BUT
- obtained in decerebrate ferret
- prelim data suggests pC behavee similarly
but still some probs with identification of relevant region of cortex.

Question 9

caution - cerebellar cortex in initial learning

Answer 9

Boele et al 2013
current evidence supports key role of cerebellar cortex in initial learning - it is possible that PC firing subsequently produce learning in deep nuclei

Question 10

BUT why deep nuclear inactivation also effective at blocking learning?

Answer 10

The loop - interpositus nucleus projects back to inferior olive.
Inactivation of interpositus disinhibits inferior olive
= increases complex spikes in cortex
which leads to fewer simple spikes- in effect cortical inactivation

Question 11

Zucca et al 2016

- the loop

Answer 11

electrophysiological evidence suggests that increasing inferior olive firing rates

• abolishes simple spikes in cortex
• suppresses eyeblink response