Nature of Plasticity in Eyeblink Conditioning

Question 1

How does synaptic plasticity produce classical conditioning?

Answer 1

Synaptic plasticity acts to reduce firing in PCs

Question 2

Who conducted electrophysiological recordings of PCs to assess their role in learning (CC)?

Answer 2

Jirenhead et al. (2007)

Question 3

What did Jirenhead et al. (2007) find?

Answer 3

Recorded from the cortical eyeblink area in lobule HVI- recorded what happened during CC

First trial- PCs were firing normally, no effect on the CS

Once learning was complete- relevant cortical PCs ceased firing, as predicted

Absence of firing of relevant PCs during acquision of the CR reflected that learning was complete.

Question 4

We pick a task that produces no effect until conditioned, e.g. a quiet tone, so when we condition that response, what occurs?

Answer 4

Excitation via the synapses between PFs and PCs which balances the inhibitory effect that occurs via inhibitory interneurons (stellate and basket cells)

Question 5

What do we pair during conditioning?

Answer 5

CS paired with UCS
Firing in PFs paired with firing in CFs

Question 6

What does theory predict will happen in conditioning?

Answer 6

PF-PC synapses become less effective by a process called LTD

Question 7

What is assumed about the inhibitory pathway during conditioning?

Answer 7

That the inhibitory pathway is unchanged and that the PCs receive a net inhibitory input when the CS comes on, so the PC pauses, releasing firing in the anterior interpositus nuclei

Question 8

Who modelled the role of LTD in CC?

Answer 8

Medina & Mauk (2000)

Question 9

How does synaptic plasticity produce CC?

Answer 9

Models predict that LTD of synapses between PFs and PCs produces CRs

Question 10

Is there evidence for LTD?

Answer 10

Yes

Ito (1984)
Ito (2002)

Stimulate PFs and CFs together
Find after conditioning the PC response is reduced

Clear evidence of LTD in cerebellar slices

Question 11

What is the role of LTD in CC?

Answer 11

Almost none

Question 12

What is a limitation of using slices?

Answer 12

They are unnatural, no afferents, no blood supply – We cannot assume that processes observed in slices are necessarily present in the intact brain

Even if LTD observed in slices was present in the intact brain, it might not be there for learning, it might have a protective function (De Schutter, 1995)

Question 13

What did De Schuttter (1995) suggest was the function of LTD?

Answer 13

Normalising the excitation of PCs

Question 14

What can slice work offer us?

Answer 14

Hypotheses about functions in the whole animal

Question 15

Beyond slice work, what else do we need?

Answer 15

Experiments that link biochemistry and behaviour to test those hypotheses

Question 16

What mice could we use to test hypotheses about LTD’s role in CC?

Answer 16

Knock-out mice

Question 17

What are knock-out mice?

Answer 17

Mice genetically engineered to lack a particular aspect of cellular processing, lacking necessary cellular machinery

Question 18

What did Schonewille et al. (2011) find?

Answer 18

Mice lacked LTD in slices, but showed normal eyeblink conditoning- so LTD is not involved in CC

Question 19

What mice do not show CC?

Answer 19

Mice lacking LTP

Question 20

What is LTP in the context of cerebellar learning?

Answer 20

When pairing a stimulus with CF discharge results in the firing PF synapses increasing in strength

Question 21

What is the covariance learning rule for supervised learning?

Answer 21

If input signal is positively correlated with error, decrease its influence

If negatively correlated, increase it’s influence

Correlation treated as cause

Question 22

Describe cerebellar implementation?

Answer 22

Increasing the influence of signals positively associated with error appears to be accomplished by increasing the influence of the inhibitory interneurons- stellate and basket cells

This is a consequence of the fact that individual synapses are either excitatory or inhibitory, so we need a parallel pathway with excitatory and inhibitory inputs

Question 23

What does the CS tone do during conditioning?

Answer 23

The CS tone decreases PC firing rate, the inhibitory input gets bigger (rather than the argument that the PF-PC synapse gets smaller)

Question 24

What is the bigger picture?

Answer 24

We can apply these findings to motor control in general

Need to know how big a command to send to muscles wherever the target is located

Question 25

How do we know how big a motor command to make?

Answer 25

Use the error signal

Question 26

Apply this to motor control in general.

Answer 26

Know when an error has occurred
Change control signal in appropriate direction

Question 27

What is an adpative filter?

Answer 27

Long been used in control of artificial systems
It takes relevant information about the motor command to be carried out and the context in which it is carried

Question 28

What did Dean et al. (2011) find about the cerebellum as an adaptive filter?

Answer 28

Most models of cerebellar function are now some form of adaptive filter

Directly relevant to motor control in a wider context

Question 29

What can we think of the cerebellum as?

Answer 29

An operating system

Question 30

How is the cerebellum an operating system?

Answer 30

Point and click- carries out high-level instructions without you being aware of what is going on
These instructions originate elsewhere e.g. cerebral cortex

Frees up system so that you can e.g. carry on walking or talking or thinking about what to do or say next