Dean NMR 3

Question 1

What is the next step now the cerebellum has been implicated in NMR conditioning?

Answer 1

Locate the site(s) of synaptic plasticity that mediate simple delay conditioning of the NMR
Can get candidate sites from circuit details

Question 2

What possible sites would be candidates for the plasticity underlying NMR conditioning?

Answer 2

The CS input and US input both arrive at lobule HVI of the cerebellum, CS via mossy fibres and US via climbing fibres
The synapses of the cells at which these 2 inputs meet would be candidate sites

Question 3

What is the background of the cerebellum?

Answer 3

Located at the base of the brain, looks like a small version of cerebral cortex
But has tighter folds than cerebral cortex
Has its own cortex which can cause confusion

Question 4

What are the 2 parts of the cerebellum?

Answer 4

Extensive cerebellar cortex (where parallel fibres and climbing fibres synapse onto the purkinje cells of lobule HVI)
Compact deep nuclei (where mossy fibres and climbing fibres synapse onto neurons in the IPN)

Question 5

Who investigated the basic circuitry of the cerebellum?

Answer 5

Eccles et al. (1967) who described

1. the structure of each of the cell types in the cerebellum
2. their synaptic connections
3. their electrophysiology

Question 6

What did Eccles et al. (1967) find?

Answer 6

The basic info flow through the cortex is simple

• Mossy fibres excite granule cells
• Granule cell axons (parallel fibres) excite purkinje cells which inhibit the deep cerebellar nuclei

Question 7

What can be said about mossy fibre inputs from the CS (tone)?

Answer 7

Mossy fibres convey information about the tone CS to area HVI, and the frequency of the signals probably increases with tone intensity
They are called mossy fibres due to their appearance

Question 8

What is the function of granule cells?

Answer 8

The mossy fibres synapse with granule cells
The axons of these granule cells form parallel fibres which synapse onto the dendrites of purkinje cells
There are many granule cells, ~80% of all neurons in the human brain are granule cells
About 100 granule cells per mossy fibre - referred to as expansion recoding

Question 9

What are purkinje cells?

Answer 9

they have cell bodies in the middle layer of the cerebellar cortex and are the only output cells of cerebellar cortex.
Each cell receives ~150,000 parallel fibre synapses
They are the largest cells in the cerebellar cortex and have a distinctive dendritic field flattened out like a fan

Question 10

What are golgi cells?

Answer 10

They get input from parallel fibres, mossy fibres and granule cells
Project back to the synapses between mossy fibres and granule cells as feedback
They’re inhibitory so the more parallel fibre input they get the more they reduce it - regulating information flow and controlling expansion recoding

Question 11

What are stellate cells?

Answer 11

Inhibitory and get input from parallel fibres, up in the molecular layer of the cerebellar cortex
They synapse with purkinje cell dendrites

Question 12

What are basket cells?

Answer 12

Inhibitory and get input from parallel fibres up in the molecular layer of the cerebellar cortex
They synapse with purkinje cell body

Question 13

What is the function of stellate and basket cells?

Answer 13

Presumed to balance the average excitatory drive from parallel fibres
When you stimulate them you can silence the spontaneous firing of purkinje cells

Question 14

Describe the spontaneous firing of purkinje cells

Answer 14

They fire simple spikes usually about 50 spikes/second

Parallel-fibre input can increase this rate to >200 spikes/second

Question 15

Outline the activity and circuitry of climbing fibres

Answer 15

Inputs for the US
has cell bodies in the inferior olive and typically fires at low frequencies e.g. ~1 spike/second
It is wrapped around the purkinje cell dendrites and acts as an enormous synapse
Has complex spikes with unusual shape, which are very reliable due to the wrapping, so when the climbing fibre fires so does the purkinje cell

Question 16

What is the function of climbing fibre input?

Answer 16

Long term depression (LTD)
Possible acts to alter the efficiency of parallel fibre synapses on purkinje cells
This fits with the reliability of CFs and the lack of effect on output
Also fits with the idea of CF conveying an error signal

Question 17

What is the second candidate aside from the purkinje cells in the cerebellar cortex?

Answer 17

The IPN as the information from mossy fibres (CS) and climbing fibres (US) also come together here
However, much less is known about the electrophysiology

Question 18

Whats a key question about this research?

Answer 18

Whether a role in NMR conditioning can be related to general functions of the cerebellum

Question 19

What is the general function of the cerebellum?

Answer 19

Cerebellar damage doesn’t cause paralysis but makes movements inaccurate slow and uncoordinated
Other parts of the brain e.g. motor cortex may issue movement commands but the cerebellum ensures they are carried out properly

Question 20

What did Brindley (1964) suggest?

Answer 20

that the purpose of the cerebellum is to learn motor skills so that when they have been learned a simple or incomplete message from the cerebrum will suffice to provoke their execution e.g. like a computer shortcut

Question 21

What do mossy fibre inputs generally convey?

Answer 21

Aside from NMR conditioning, they convey the current state of the body and current motor commands

Question 22

What are climbing fibres related to?

Answer 22

Difficult to relate it to specific inputs but usually related to sensory signals such as touch, pain, and visual inputs

Question 23

What is the structure and organisation of the cerebellar modules?

Answer 23

The individual areas of the cerebellar cortex are all packed together but functionally distinct despite having a uniform surface.
They receive inputs from different regions and the external wiring is extremely diverse

Question 24

What is the idea of the ‘cerebellar chip’?

Answer 24

The same basic piece of circuitry can be plugged into different parts of the brain
It is responsible for learning motor skills, regulation of emotion and behaviour, and possible dyslexia and autism??
But also responsible for simple NMR conditioning

Question 25

What are the implications of this cerebellar chip?

Answer 25

That an exchange is possible
NMR conditioning can borrow ideas from general theories of cerebellar function
Insights from NMR conditioning can also be used to improve general theories
Understanding how the cerebellar chip works may also help us build better robots