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 VORreflex 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 combinationsprovide the sensory context

Sensory

context

Climbing fibre•Covers whole dendritic tree of Purkinke cell•All-or-nothing acitvation•Co-activation of climbingfibre and parallel fibreLeads to LTD of theparallel fibre synapse.

Interneurons.Golgi for Granule cellsBasket and Stellate for Purkinje cells•Inhibitory•(GABA, glycine etc)•Diversity increasesWith cerebellar complexity(greatest variety in anthropoid primates)

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Time-to-Place Conversion:•Purkinje cells along “beam”of parallel fibrese.g. 10 m/sec gives 10 mm/msecor 10 m/sec.So a 10 m spacingbetween Purkinje cells allows a time resolutionof 10 sec.Electric fish achieve nanosecond timing with

larger, faster beams.

Time-to-Place Conversion:•Purkinje cells along “beam”of parallel fibrese.g. 10 m/sec gives 10 mm/msecor 10 m/sec.So a 10 m spacingbetween Purkinje cells allows a time resolutionof 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