Summary of Lecture 3VETS2011Cerebellum

• Demo of VOR in owl: VOR plasticity• World record cerebellum: Electric fish: nanosecond timing• Summary of structure and function in cerebellum• Time-to-place conversion• Adaptive plasticity of VOR (Owl, “wet head example”)• Contrast procedural learning with declarative memory

Procedural Memory

• Gain of reflexes (e.g. VOR)

• Conditioned reflexes (e.g. eye blink)

• Skilled sequences (e.g. cycling, typing)

Vestibulo-Ocular Reflex (VOR)

• Fastest reflex in brain• Operates “perfectly” without cerebellum (i.e. same conditions)• But gain adaptation requires cerebellum (i.e. as conditions change, such as growth,

ageing, muscle strength, oxidative damage etc)

VOR circuit:

1. Vestibular hair cell

2. Vestibular neuron

3. Oculomotor neuron

Only 2 synapses.

Purkinje cell modulates VOR

reflex at vestibular neuron

Trout Electric Fish

Basic fish Electric Fish

Forebrain

Cerebellum

Purkinje Cell.

•Only output of cerebellum

•GABAergic inhibition•106 spine synapses

•Spines modifiable by LTD

• Climbing fibre“Punishes”

co-active spine synapses

•“Espalier “ shape enables tight packing in coronal plane despite huge sagittal arbour: gives “delay line”.

Excitatory Inputs.

•Mossy fibre to

granule cells to

parallel fibres to

spine synapses

on Purkinje cells

•Vast combinations

provide the sensory

contextSen

sory

contex

t

Climbing fibre•Covers whole

dendritic tree of

Purkinke cell•All-or-nothing acitvation•Co-activation of climbing

fibre and parallel fibre

Leads to LTD of the

parallel fibre synapse.

Interneurons.Golgi for Granule cells

Basket and Stellate for Purkinje cells•Inhibitory•(GABA, glycine etc)•Diversity increases

With cerebellar complexity

(greatest variety in

anthropoid primates)

12

34

Time-to-Place Conversion:

•Purkinje cells along “beam”

of parallel fibres

e.g. 10 m/sec gives 10 mm/msec

or 10 m/sec.

So a 10 m spacing

between Purkinje cells

allows a time resolution

of 10 sec.

Electric fish achieve

nanosecond timing with

larger, faster beams.

Time-to-Place Conversion:

•Purkinje cells along “beam”

of parallel fibres

e.g. 10 m/sec gives 10 mm/msec

or 10 m/sec.

So a 10 m spacing

between Purkinje cells

allows a time resolution

of 10 sec (humans).

Electric fish achieve nanosecond

timing with larger, faster beams.

1020

30

0

sec

Declarative vs Procedural Memory

• Forebrain: Bilateral• Single trial possible• “Creative”; fraction of inputs • LTP• cAMP 2nd messager• Error-prone• ?Sleep needed

• Hindbrain:Midline• Many trials needed• “Stupid”: needs all inputs• LTD• cGMP 2nd messager• Precise• Corrected in waking state