Neuronal Map Formation & Time-Resolved Learning: Do Different Modalities "Observing" the Same Object Compete?

A map is a neuronal representation of the outside sensory world. Spike-timing-dependent synaptic plasticity (STDP) is a universal means to ``learn'' spatio-temporal neuronal activity patterns [1] and explain neuronal map formation [2]. Time resolution may well, and does, happen at a millisecond timesale or better. For example, in the barn owl STDP resolves the Konishi paradox of attaining an accuracy ($\mu$s) that is two orders of magnitude better than all neurnal time constants involved and explains the full neuronal map in the laminar nucleus, where inputs from left and right ear convene.

Quite often, however, STDP is not completely self-organizing but needs an external "teacher" to coordinate maps arising from two, or more, different sensory modalities. To this end supervised STDP (SSTDP) may be quite helpful [3]. Here we explain SSTDP through two concrete examples, the clawed frog Xenopus and the barn owl. For the latter it is known since long that the visual system is the teacher, for the former we surmise it is in an early stage of the frog's existence. We also discuss a convergence proof for the algorithm underlying SSTDP.

[1] W. Gerstner, R. Kempter, J.L. van Hemmen, and H. Wagner, A neuronal learning rule for sub-millisecond temporal coding, Nature 383 (1996) 76-78.
[2] C. Leibold and J.L. van Hemmen, Spiking neurons learning phase delays: How mammals may develop auditory time-difference sensitivity, Phys. Rev. Lett. 94 (2005) 168102-1/4
[3] J.-M.P. Franosch, M. Lingenheil, and J.L. van Hemmen, How a frog can learn what is where in the dark, Phys. Rev. Lett. 95 (2005) 078106-1/4