Lecture 9 Flashcards
where is the cerebellum placed in the hierarchical sensory-motor organization?
the cerebellum is well placed within the motor system to receive sensory information from they eyes, the ears, the limbs
And it uses this sensory input to integrate that with essentially a prediction of what movements we want to perform to help us execute movements which are both smooth, accurate, and executed without any problems or delays or errors
where is the cerebellum placed in the skull?
at the back underneath part of the brain
it is constantly monitoring what’s happening in the real world
it is always aware of what’s going on in the environment
what is the cerebellum?
· Massive cortical area, but much simpler than cerebral cortex – only 1 output layer.
· Heavily folded.
· Exerts influence on movement via influence on motor and pre-motor cortex.
· Also connects with brainstem and spinal cord.
· Adds coordination, fine control, skill to basic movement patterns.
· A powerful learning machine.
what does the length of the cerebellar cortex reflect?
body mass
what does the width of the cerebellar cortex may reflect?
cognitive properties?
it is much larger (in length and width) in humans compared to other animals
what cell is mainly for motor learning?
Purkinje cells
where structurally is the purkinje cell located?
between molecular and granular
surrounded by the climbing fibres and mossy fibres
how do cerebellar cortical connection occur/work?
Sensory information is taken in and arriving through these mossy fibres
This projects onto the granule cells, this is where the axons make up the parallel fibres
This then travels through the purkinje cells
Climbing fibres are sending information about the actual movement we want to perform
what does the cerebellar cortical circuit allow the cerebellum to do?
allows the cerebellum to refine movements, detect errors, and facilitate motor learning through precise modulation of output signals
what is the cerebellar nuclei?
So the output from the cerebellum to the rest of the brain would be through what are called these deep cerebellar nuclei (the green part) [check notes]
They send output to the motor structures of the cerebral cortex to update your movements to ensure that they’re performed accurately and smoothly
If the movement performed wasn’t accurate, then the cerebellum is capable of changing your movements to ensure that the next time is accurate
how are the cortex-cerebellar loops evidence for different kinds of sensory inputs?
So evidence for different kinds of sensory inputs arriving in the cerebellum has been demonstrated using
MRI studies
So you can put people in a brain scanner, record what the cerebellum is doing (how it is active when it is receiving information from different sensory parts of the brain), and its possible to identify regions of interest that are associated with different parts of the cerebral cortex
what are the types of cerebellar damage?
- Hypermetria (overshoot): finger-to-nose (tests for motor coordination)
- Intention tremor: during action
- Ataxia: loss of (motor) coordination, and skill(ful movement)
- Nystagmus (flickering of eye movements), balance, gait (walking), speech
Essentially drunk like behaviour whilst sober - Cerebellar affective disorder: executive, emotional, personality (children)
What is the “Marr-Albus” model of learning?
· 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.
- A decrease in Purkinje cell activity associated with learning
what are the four examples of cerebellar learning?
- Vestibular Ocular Reflex (VOR)
- Eye Blink conditioning
- Skill Learning
- Visuo-motor recalibration
what is the Vestibular Ocular Reflex?
The Vestibulo-Ocular Reflex (VOR) is a mechanism that helps stabilize vision during head movement by producing eye movements that counteract head motion.
Input (into the cerebellum) : vestibular system signal of head motion
Output (from the cerebellum) : modulation of direct path to ocular motor neurons
what occurs when VOR gain is too weak?
- Retinal slip drives LTD
- Reduced excitation of P-cell
- Dis-inhibition of vestibular nucleus = stronger drive = higher gain
what is the eye blink conditioning?
A rabbit is played a tone whilst a puff of air is blown simultaneously
Classical conditioning Lesion of cerebellum causes failure to learn
Unconditioned Stimulus: puff of air into eye (also activates climbing fibres)
Unconditioned Response: eyeblink
Conditioned Stimulus: a tone or light (activates parallel fibres)
Conditioned Response: learned eyeblink to avoid air-puff
So Purkinje cells are receiving info about the auditory tone that the animal hears from the auditory cortex, it also receives info about the puff of air from the climbing fibres
Input received at the same time by the Purkinje cells, increases learning because cells that fire together wire together
what is skill learning?
Once the animal has learned how much to twist that device to keep the weight balanced, as this is the skill the animal is having to do, you can see how the spiking activity of Purkinje cells is kind of related to the onset and offset of the movements at the beginning and the end of that movement
Which you didn’t see before learning, so you can now see the consequences of learning associated with this task
what is visuo-motor recalibration?
· Prism glasses distort visual inputs – need to adjust movement output to recalibrate
Glasses would turn the world upside down e.g. you’d move your arm upwards but you’d see it moving downwards through the goggles
· Short term learning of visuo-motor relationship
· Learning blocked by cerebellar lesions
summarise the role of the cerebellum
· Cerebellar cortex: big and (relatively!) simple
· Important for all skilful movement
· Huge numbers of parallel fibres bring very diverse sensory-motor input to Purkinje cells
· Climbing fibres induce parallel fibre : P-cell LTD – the main (but not only) mechanism
· Adjusts VOR gain, support classical conditioning of eye-blink (& other reflexes)
· Predictive control
draw the diagram for normal throwing
motor cortex -> body
motor cortex -> cerebellum
-> prediction outcome -> prediction vs actual = no error -> no need to update anything -> motor cortex
draw adaptation (update of error) diagram
motor cortex -> body
motor cortex -> cerebellum -> predict outcome -> prediction vs actual = ERROR -> update motor commands to account for this error
draw the diagram for cerebellar prediction
motor cortex -> body
motor cortex -> cerebellum -> prediction of sensory feedback based on motor commands -> compare prediction versus actual sensory feedback -> update motor commands so that error is reduced
how does damage to the cerebellum affect prediction?
If you’ve got damage to the cerebellum, then you shouldn’t be able to make a prediction to a mismatch between what you see and what you do
You shouldn’t be able to learn or adapt from this discrepancy between what you’re looking at and the movements that you’re performing
