the data-driven cerebellum

  • with the motor hierarchy alone, we will not move the way we actually move
  • the two areas that modulate movement are
    • cerebellum
    • basal ganglia
  • cerebellum is the brocoli-like brain component which sits behind the stem like hind brain
    • pons and the cerebellum share a connection
  • it looks like a sensory area judging from the number of inputs from the body system
    • but, when it is damaged, the symptoms are motor in appearance
    • ataxia is a cardinal sign of cerebellar damage
  • cerebellum receives visual, vestibular, and somatosensory (from the neck primarily) sensory information
    • cerebellum has a clear role in motor coordination
  • cerebellum is a data driven structure
    • it uses data from the individual body into that body making smooth movements
    • it doesn’t have an inherent program
    • helps accommodate changes in the body over time
    • it has no priori assumptions of what body is going to be like
  • cerebellum is like a computer chip that transforms inputs into an output
    • the nature of the transform is still a study in process
    • the output is of both motor and non-motor function in nature

the purkinje cell

  • there is lacking consensus among what the transform is going from the basics of cerebellum to its function

  • purkinje cell is a cell body that is ~50-70 microns in diameter
    • with enormous dendritic arborization in one plane
    • it is flat in the other plane
    • so it is extremely oriented
  • the dendrites are dotted with spines
    • it ends in an axon

cerebellar function

  • motor learning

  • motor coordination/execution

  • well set motor memory is virtually impossible to forget
    • this is why babies practice walking
    • i.e. you cant forget how to ride a bike
  • this is contrary to the spinal cord reflexes
    • they don’t last long and cannot be remembered without practice
  • motor execution examples
    • going from walking on concrete to beach to on a ship

cerebellar topography

  • cerebellar function is topographically arranged
  • central vermis modulates central movements
    • posture
    • gait
    • speech
  • adjacent para-vermis modulates outside organs
    • hands limbs
    • fingers modulation
  • large peripheral lateral lobes
    • the base of the pons in married to this
    • only in primates and up including dolphins
    • modulates playing music and such fine skills
    • can’t relearn new motor skills if damaged
    • assessing emotional temperature of a group
    • motor to non-motor translation
    • but clear consensus doesn’t exist
  • flocculus modulates eye movements
    • for vestibular ocular movement
    • for latching gaze on to a bird’s path across the sky smoothly

cerebellar laterality

  • left motor cortex controls the right muscles and vice-versa
    • touch pain and temperature sensory of right body goes to left cortex
  • but the sensory information from the same side arrives on the same side of the cerebellar cortex (ipsilateral - i.e. same side)
    • having crossed the midline in the pons coming down
    • going up, the information side becomes opposite
  • cerebellum is bridged to the pons through the peduncles
    • damage to cerebellum or the peduncles causes the same effect

intent matching and learning

  • the cerebellum has 40 times more input that it has outputs
    • counting then umber of axons
  • two basic types of inputs;
    • efferent copy (afferent(coming in) vs efferent(going out))
      • muscles actuation copy is also sent to cerebellum
      • it monitors intent by comparing what was sent by the cortex in the upper head to what the muscle actuation received
        • feedback control difference
    • sensory re-afference
      • the sensory inputs that come as a result of the command sent
      • a comparison of what was sent to the happen and the results of what happened
  • this helps to ensure the actual movement matched the intended movement
    • similar to feedback control
    • when this not true, cerebellum makes a course correction
      • this is how it causes learning
      • the process is called associative learning
  • a sensory image of a resulting action is used to match the intent that produced it in the first place
    • the right sensory feedback for having done the act right is anticipated continuously
    • it “feels wrong” if there is deviation between the sensory feedback and the intended movement

  • cerebellum is about smooth motor control using sensory information

  • writing, sculpting, etc are learnable movements
    • this is possible through the cerebellum
    • it can invent new motion
  • lateral lobes do the learning of new patterns
    • the vermis and the para-vermis do the execution
  • doing it without thinking about it when the cerebellum has learnt the new move
    • if thinking about it then the upper brain gets involved

VOR

  • VOR: vestibulo-ocular reflex
    • cerebellum is very involved with eye movements and the vestibular system
    • one of the most important reflex we have
  • VOR moves eye in opposition to head movement to steady ones gaze to focus on something
    • the vestibular system is extremely fast
      • used to guide eye when the head is moving
    • the visual system is slow relatively
  • all reflexes have to be modulated
    • VOR is no exception
  • VOR varies for objects close by and faw away
    • as per distance
    • this modulation is brought about by Vestibular cerebellum
      • called the flocculus and nodulus
      • it can be turned off as intended
    • if the head itself moves, then the VOR has to be turned off
    • changing the gain of the VOR requires the cerebellum
  • if the cerebellum is damaged, then the eyes move with the head all the time