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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
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Procedural Memory
• Gain of reflexes (e.g. VOR)
• Conditioned reflexes (e.g. eye blink)
• Skilled sequences (e.g. cycling, typing)
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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)
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VOR circuit:
1. Vestibular hair cell
2. Vestibular neuron
3. Oculomotor neuron
Only 2 synapses.
Purkinje cell modulates VOR
reflex at vestibular neuron
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Trout Electric Fish
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Basic fish Electric Fish
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Forebrain
Cerebellum
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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”.
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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
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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.
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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)
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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.
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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
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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