All summary questions- classical conditioning

Question 1

Strategy for studying neural basis of memory?

Answer 1

– Need to pick a simple task to start with

Question 2

– Suitable simple task?

Answer 2

– Eyeblink conditioning has been well studied.

– Simplest version: delay conditioning of nictitating membrane response (NMR)

Question 3

Where in brain are the plastic synapses that mediate this conditioning?

Answer 3

– In people, medial temporal lobe damage prevents formation of new long-term memories, but has little effect on eyeblink conditioning
– In rabbits the forebrain not needed for delay NMR conditioning
– But both electrophysiological and lesion studies implicate the cerebellum

Question 4

How to establish circuitry underlying delay NMR conditioning?

Answer 4

– Use standard neuroscience techniques
• Anatomy
• Electrophysiology
• Manipulation

Question 5

Circuitry can be broken down into 5 parts

Answer 5

– Unconditioned reflex pathway
– Output of anterior interpositus nucleus controlling the conditioned response
– Output of eyeblink region of cerebellar cortex controlling the anterior interpositus nucleus
– Eyeblink region receives information about conditioned stimulus via mossy fibres
– Eyeblink region receives information about unconditioned stimulus via climbing fibres

Question 6

What are the main cell types in cerebellar cortex?

Answer 6

– Purkinje, granule, Golgi, stellate, basket.

Question 7

How are they connected?

Answer 7

– See circuit diagram

Question 8

Where are the potential sites of plasticity?

Answer 8

– Purkinje cell dendrites receive information about the CS from parallel fibres, and about the US from climbing fibres
– Cells in anterior interpositus nucleus also receive these inputs

Question 9

How is eyeblink conditioning related to other ‘cerebellar’ tasks?

Answer 9

– They are all mediated by the same basic neural circuit

Question 10

General theories of cerebellar function: what task do they model?

Answer 10

– Making sure movements are accurate

Question 11

What methods (algorithms) have been proposed?

Answer 11

– Supervised learning: an error signal makes movements bigger or smaller as required

Question 12

How does learning theory work in cerebellum?

Answer 12

– Mossy fibres convey input information
– Climbing fibres convey error information
– Latter used to depress synapses contributing to error (LTD)

Question 13

Can this general theory be applied to eyeblink conditioning?

Answer 13

– In principle yes. In practice?

Question 14

Where are the plastic synapses in NMR conditioning?

Answer 14

– Modelling predicts the synapses between granule cells and Purkinje cells

Question 15

Evidence: are plastic synapses in cerebellum or brainstem?

Answer 15

– Several lines of evidence strongly point to the cerebellum

Question 16

Are plastic synapses in cerebellar cortex, or the deep cerebellar nuclei

Answer 16

– Evidence increasingly indicates that the cerebellar cortex mediates initial learning

Question 17

Is there any plasticity in the deep nuclei?

Answer 17

– Perhaps with extended training

Question 18

What kind of synaptic plasticity was predicted to underlie eyeblink conditioning?

Answer 18

– LTD at the synapses between parallel fibres and Purkinje cells

Question 19

What is evidence for LTD at these synapses?

Answer 19

– Generally agreed that in slices LTD can be demonstrated reliably

Question 20

How does it work?

Answer 20

– Unclear: one suggestion is activation of mGluR1 receptors (in conjunction with climbing fibre input)

Question 21

Does this apply to actual conditioning in vivo?

Answer 21

– A quite different mechanism involving mGluR7 receptors has been implicated
– What (if any) role LTD plays is unclear