Nature of Plasticity in Eyeblink Conditioning Flashcards
How does synaptic plasticity produce classical conditioning?
Synaptic plasticity acts to reduce firing in PCs
Who conducted electrophysiological recordings of PCs to assess their role in learning (CC)?
Jirenhead et al. (2007)
What did Jirenhead et al. (2007) find?
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.
We pick a task that produces no effect until conditioned, e.g. a quiet tone, so when we condition that response, what occurs?
Excitation via the synapses between PFs and PCs which balances the inhibitory effect that occurs via inhibitory interneurons (stellate and basket cells)
What do we pair during conditioning?
CS paired with UCS
Firing in PFs paired with firing in CFs
What does theory predict will happen in conditioning?
PF-PC synapses become less effective by a process called LTD
What is assumed about the inhibitory pathway during conditioning?
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
Who modelled the role of LTD in CC?
Medina & Mauk (2000)
How does synaptic plasticity produce CC?
Models predict that LTD of synapses between PFs and PCs produces CRs
Is there evidence for LTD?
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
What is the role of LTD in CC?
Almost none
What is a limitation of using slices?
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)
What did De Schuttter (1995) suggest was the function of LTD?
Normalising the excitation of PCs
What can slice work offer us?
Hypotheses about functions in the whole animal
Beyond slice work, what else do we need?
Experiments that link biochemistry and behaviour to test those hypotheses
What mice could we use to test hypotheses about LTD’s role in CC?
Knock-out mice
What are knock-out mice?
Mice genetically engineered to lack a particular aspect of cellular processing, lacking necessary cellular machinery
What did Schonewille et al. (2011) find?
Mice lacked LTD in slices, but showed normal eyeblink conditoning- so LTD is not involved in CC
What mice do not show CC?
Mice lacking LTP
What is LTP in the context of cerebellar learning?
When pairing a stimulus with CF discharge results in the firing PF synapses increasing in strength
What is the covariance learning rule for supervised learning?
If input signal is positively correlated with error, decrease its influence
If negatively correlated, increase it’s influence
Correlation treated as cause
Describe cerebellar implementation?
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
What does the CS tone do during conditioning?
The CS tone decreases PC firing rate, the inhibitory input gets bigger (rather than the argument that the PF-PC synapse gets smaller)
What is the bigger picture?
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
How do we know how big a motor command to make?
Use the error signal
Apply this to motor control in general.
Know when an error has occurred
Change control signal in appropriate direction
What is an adpative filter?
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
What did Dean et al. (2011) find about the cerebellum as an adaptive filter?
Most models of cerebellar function are now some form of adaptive filter
Directly relevant to motor control in a wider context
What can we think of the cerebellum as?
An operating system
How is the cerebellum an operating system?
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
