Topic 8: Cerebellum Flashcards
What is the cerebellum’s role in the Hierarchical sensory-motor organization
What happens if there is damage to the cerebellum?
integration
if you had damage to the cerebellum, movements would be uncoordinated
What is the cerebellum also known as?
How many layers has it got?
how is it folded?
what does it influence?
where is it connected to?
- Little brain - powerful learning machine
- 1 layer
- Heavily folded
- Movement - via motor and pre-motor cortex, coordination, fine control, skill to basic movement patterns
- Connected to the brainstem and spinal cord
What does length and width reflect in the cerebellum?
length reflects body mass
width may reflect cognitive properties
how many cells in the human cerebellum
Total (102 billion): 102,000,000,000
Granule cells 101,000,000,000
Purkinje cells 15-30,000,000
Golgi, basket, stellate 150-200,000,000
Nuclear cells 5,000,000
Purkinje cell inputs:
from Parallel fibres 200,000
from Climbing fibres 1
Take home: many many cells for a small component of the brain
What layers have you got in the cerebellar cortex
What are the two inputs into the cerebellum?
How are they connected to each other?
Molecular >
Purkinje granular > climbing fibres > mossy fibres
1) mossy fibres > connect to granular cells > granular cells have parallel fibres which shoot through purkinje cells and have many connections
2) climbing fibre (from the inferior olive), it is wrapped around one single purkinje cell
Remember inputs: climbing and mossy
Where does purkinje cells output go?
purkinje cells output connects deep cerebellar nuclei > connects to thalamus > rest of cortex
what are three sections of the cerebellum
1) Vermal
2) Intermediate/paravermal
3) Lateral hemisphere
are purkinje cells excitatory or inhibitory?
purkinje cells are inhibitory on the cerebellar nuclei - stops it sending outputs
What are 5 disorders caused by damage to cerebellum
Hypermetria: causes overshooting of finger to nose (coordination)
Intention tremor: tremor that occurs during action
Ataxia: loss of coordination and skill
Nystagmus: involuntary oscillation of the eyes - balance, gait, speech
Cerebellar affective disorder: executive, emotional, personality, particularly in children
What is the “Marr-Albus” model of learning?
Theory of how the cerebellum learns involving teaching signals and plasticity
- The synapse between granule cells (parallel fibres) and Purkinje cells is plastic, and can undergo Long Term Depression (LTD)
- The trigger for LTD is simultaneous activity of parallel fibres and climbing fibres (associative learning) via mossy fibres, error signal via climbing fibres
- LTD reduces P-cell inhibition of cerebellar nuclei, and dis-inhibits the direct pathway
What are four example of cerebellar learning?
1) Vestibular Ocular Reflex (VOR)
3) Eye Blink conditioning
4) Skill Learning
4) Visuo-motor recalibration
1) Vestibular Ocular Reflex (VOR)
Input : vestibular system signal of head motion
Output : modulation of direct path to ocular motor neurons
Consider: VOR gain too weak
Retinal slip drives LTD
Reduced excitation of P-cell
Dis-inhibition of vestibular nucleus = stronger drive = higher gain
2) Eye blink conditioning
Classical conditioning Lesion of cerebellum causes failure to learn
US: puff of air into eye (also activates climbing fibres)
UR: eyeblink
CS: a tone or light (activates parallel fibres)
CR: learned eyeblink to avoid air-puff
3) Skill learning
Assumption of LTD
Not easy to measure LTD in intact, behaving animals
But can record complex spikes
4) Visuo-motor recalibration
Prism glasses distort visual inputs – need to adjust movement output to recalibrate
Short term learning of visuo-motor relationship
Learning blocked by cerebellar lesions
