Summary of Lecture 2 Cerebellum

1
Summary of Lecture 2Cerebellum

• Demo of VOR in owl VOR plasticity
• Contrast procedural learning with declarative
  memory
• World record cerebellum Electric fish
  nanosecond timing
• Summary of structure and function in cerebellum
• Time-to-place conversion
• The concept of efference copy
• fMRI experiments on tickling

2
(No Transcript)
3
Procedural Memory

• Gain of reflexes (e.g. VOR)
• Conditioned reflexes (e.g. eye blink)
• Skilled sequences (e.g. cycling, typing)

4
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)

5

• VOR circuit
• 1. Vestibular hair cell

2. Vestibular neuron
3. Oculomotor neuron
Only 2 synapses. Purkinje cell modulates
VOR reflex at vestibular neuron
6
Trout Electric Fish
7
Basic fish
Electric Fish
8
(No Transcript)
9
Forebrain
Cerebellum
10

• Purkinje Cell.
• Only output of cerebellum
• GABAergic inhibition
• 106 spine synapses
• Spines modifiable by LTD
• Climbing fibrePunishes
• co-active spine synapses

11

• Excitatory Inputs.
• Mossy fibre to
• granule cells to
• parallel fibres to
• spine synapses
• on Purkinje cells
• Vast combinations
• provide the sensory
• context

12

• 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)

13

• Time-to-Place Conversion
• Purkinje cells along beam
• of parallel fibres
• e.g. 10 m/sec gives 10 mm/msec
• or 10 mm/msec.
• So a 10 mm spacing
• between Purkinje cells
• allows a time resolution
• of 10 msec.
• Electric fish achieve
• nanosecond timing with
• larger, faster beams.

4
3
2
1
14

• Time-to-Place Conversion
• Purkinje cells along beam
• of parallel fibres
• e.g. 10 m/sec gives 10 mm/msec
• or 10 mm/msec.
• So a 10 mm spacing
• between Purkinje cells
• allows a time resolution
• of 10 msec (humans).
• Electric fish achieve nanosecond
• timing with larger, faster beams.

msec
30
20
10
0
15
Efference Copy

• Spatio-temporal pattern of activity that is
  copied from the motor output to the sensory
  system so that the sensory consequences of the
  motor act can be precisely annulled.
• Hallucinations are d/t aberrant efference copy
• Cerebellum produces efference copy
• Why it is hard to tickle yourself

16
Cerebellum activated by externally produced
tactile stimuli
Anterior lobe Talairach coordinates 16 -44 -32 Z
4.24 PSelf-produced tactile stimuli
Rest
Externally- produced tactile stimuli
Self-produced movement
17
Declarative vs Procedural Memory

• Forebrain
• Single trial possible
• Creative fraction of inputs
• LTP
• Error-prone
• ?Sleep needed

• Hindbrain
• Many trials needed
• Stupid needs all inputs
• LTD
• Precise
• Corrected in waking state