Learning sensorimotor transformations

1. Learning sensorimotor transformations Maurice J. Chacron

2. The principle of sensory reafference: Von Holst and Mittelstaedt, 1950

3. 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?

4. Mechanical tickling experiment: Blakemore, Frith, and Wolpert, J. Cogn. Neurosci. (1999)

5. Motor command  arm movement • Reafference  tactile stimulus • Perceived stimulus  tickling sensation

7. Wolpert and Flanagan, 2001

8. 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.

9. Adaptive cancellation of sensory reafference

10. Motor learning: Martin et al. 1996

12. Sensorimotor coordinationdoes not require the cerebellum. • Adaptation to novel conditionsdoes require cerebellar function. • Adaptation is an error driven process.

13. Cerebellar Plasticity:

14. Co-activation of parallel and climbing fiber input gives rise toLTD

15. How does cerebellar LTD help achieve cancellation of expected stimuli?

16. Weakly electric Fish • Electric fish emit electric fields through an electric organ in their tail.

17. Anatomy Trout Electric Fish

18. The 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.

19. Electrolocation

20. Electric fishuseperturbations 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?

21. Cerebellar-like anatomy: Bell, 2001

22. Bell, 2001

23. Changes in the reafferent stimulus causechanges in the efference copy • What mechanisms underlie these changes?

24. Plasticity experiment: granule cell Parallel fiber sensory input

25. Anti-Hebbian STDP: presynaptic postsynaptic

26. Cancellation of unwanted stimuli requires precise timing. • Anti-Hebbian STDPunderlies the adaptive cancellation of reafferent input.

27. How?

28. Adaptive cancellation of tail bends

29. Cerebellar-like anatomy

30. Anatomy

31. Burst firing in pyramidal cells Burst-timing dependent plasticity

32. Model of adaptive cancellation in the electrosensory system

33. Model Assumptions: How to “carve out” a negative image • 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

34. Graphically… Synaptic weights Most depression Least depression stimulus π 2π 0 Phase (rad)

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

36. Does the model work?

37. Bursting is frequency dependent

38. Bursts and isolated spikes code for different features of a stimulus Oswald et al. 2004

39. Adaptive learning

40. Summary • 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