Learning sensorimotor transformations
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Learning sensorimotor transformations. Maurice J. Chacron. The principle of sensory reafference:. Von Holst and Mittelstaedt, 1950. Movements can lead to sensory reafference (e.g. body movements) An efference copy and the reafferent stimulus are combined and give rise to the

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The principle of sensory reafference
The principle of sensory reafference:

Von Holst

and Mittelstaedt, 1950


  • Movementscan lead to sensory reafference (e.g. body movements)

  • An efference copy and the reafferent stimulus are combined and give rise to the

    perceived stimulus.

  • Question: how is the efference copy combined with the reafferent stimulus to give rise to the perceived stimulus?


Mechanical tickling experiment
Mechanical tickling experiment:

Blakemore, Frith, and Wolpert, J. Cogn. Neurosci. (1999)


  • Motor command  arm movement

  • Reafference  tactile stimulus

  • Perceived stimulus  tickling sensation


Wolpert and

Flanagan, 2001


  • The predicted sensory stimulus(efference copy)is compared to the actual stimulus

  • If there is a discrepancy, then the subject perceives the stimulus as causing a tickling sensation.

  • The efference copycontainsboth temporal and spatial information about the reafferent stimulus.



Motor learning
Motor learning:

Martin et al. 1996


  • Sensorimotor coordinationdoes not require the cerebellum.

  • Adaptation to novel conditionsdoes require cerebellar function.

  • Adaptation is an error driven process.





Weakly electric fish
Weakly electric Fish expected stimuli?

  • Electric fish emit electric fields through

    an electric organ in their tail.


Anatomy
Anatomy expected stimuli?

Trout

Electric Fish


  • The expected stimuli? cerebellum of electric fish is very developed.

  • Cerebellar anatomy is conserved across vertebrates.

  • Electric fish have “simple” anatomy and behaviors.

  • Electric fish are a good model system to study cancellation of reafferent input.


Electrolocation
Electrolocation expected stimuli?


  • Electric fish expected stimuli? useperturbations of their self-generated electric field to interact with their environment.

  • Pulses generated by the animal can activate their own electrosensory system.

  • Are there mechanisms by which sensory neurons can “ignore” these reafferent stimuli?


Cerebellar like anatomy
Cerebellar-like anatomy: expected stimuli?

Bell, 2001


Bell, 2001 expected stimuli?


  • Changes expected stimuli? in the reafferent stimulus

    causechanges in the efference copy

  • What mechanisms underlie these changes?


Plasticity experiment
Plasticity experiment: expected stimuli?

granule cell

Parallel fiber

sensory input


Anti hebbian stdp
Anti-Hebbian STDP: expected stimuli?

presynaptic

postsynaptic



How? expected stimuli?



Cerebellar like anatomy1
Cerebellar-like anatomy expected stimuli?


Anatomy1
Anatomy expected stimuli?


Burst firing in pyramidal cells
Burst firing in pyramidal cells expected stimuli?

Burst-timing dependent plasticity



Model assumptions how to carve out a negative image
Model Assumptions: How to “carve out” a negative image expected stimuli?

  • A subset of cerebellar granule cells fires at

    every phase of the stimulus

  • Probability to fire a burst is largest/smallest

    at a local stimulus maximum/minimum

  • Weights from synapses near the local maximum/

    minimum will be most/least depressed


Graphically
Graphically… expected stimuli?

Synaptic weights

Most depression

Least depression

stimulus

π

0

Phase (rad)


Extra assumptions
Extra assumptions expected stimuli?

  • Non-associative potentiation (in order to prevent the weights from going to zero).


Does the model work
Does the model work? expected stimuli?





Summary
Summary stimulus

  • Sensorimotor transformations require learning.

  • This learning must be adaptive (e.g. adapt to changes during development, etc…)

  • Anti-Hebbian plasticity provides a mechanism for adaptive cancellation of reafferent stimuli


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