All summary questions- classical conditioning Flashcards
Strategy for studying neural basis of memory?
– Need to pick a simple task to start with
– Suitable simple task?
– Eyeblink conditioning has been well studied.
– Simplest version: delay conditioning of nictitating membrane response (NMR)
Where in brain are the plastic synapses that mediate this conditioning?
– 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
How to establish circuitry underlying delay NMR conditioning?
– Use standard neuroscience techniques
• Anatomy
• Electrophysiology
• Manipulation
Circuitry can be broken down into 5 parts
– 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
What are the main cell types in cerebellar cortex?
– Purkinje, granule, Golgi, stellate, basket.
How are they connected?
– See circuit diagram
Where are the potential sites of plasticity?
– 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
How is eyeblink conditioning related to other ‘cerebellar’ tasks?
– They are all mediated by the same basic neural circuit
General theories of cerebellar function: what task do they model?
– Making sure movements are accurate
What methods (algorithms) have been proposed?
– Supervised learning: an error signal makes movements bigger or smaller as required
How does learning theory work in cerebellum?
– Mossy fibres convey input information
– Climbing fibres convey error information
– Latter used to depress synapses contributing to error (LTD)
Can this general theory be applied to eyeblink conditioning?
– In principle yes. In practice?
Where are the plastic synapses in NMR conditioning?
– Modelling predicts the synapses between granule cells and Purkinje cells
Evidence: are plastic synapses in cerebellum or brainstem?
– Several lines of evidence strongly point to the cerebellum
Are plastic synapses in cerebellar cortex, or the deep cerebellar nuclei
– Evidence increasingly indicates that the cerebellar cortex mediates initial learning
Is there any plasticity in the deep nuclei?
– Perhaps with extended training
What kind of synaptic plasticity was predicted to underlie eyeblink conditioning?
– LTD at the synapses between parallel fibres and Purkinje cells
What is evidence for LTD at these synapses?
– Generally agreed that in slices LTD can be demonstrated reliably
How does it work?
– Unclear: one suggestion is activation of mGluR1 receptors (in conjunction with climbing fibre input)
Does this apply to actual conditioning in vivo?
– A quite different mechanism involving mGluR7 receptors has been implicated
– What (if any) role LTD plays is unclear
