Eur. Biophys. J. 29: 245, 2000.

Sound localization and formation of temporal feature maps in the barn owl's auditory system

R. Kempter, C. Leibold, H. Wagner, and J. L. van Hemmen

Computational maps are of central importance to the neural representation of the outside world. In a map, neighboring neurons respond to similar sensory features. A well studied example is the computed map of interaural time difference (ITD), which is essential in sound localization in a variety of species and allows resolution of ITDs of the order of 10 microseconds. Nevertheless it is unclear how such orderly representations of temporal features arise. We address this problem by modeling the ontogenetic development of the map of ITD in the experimentally well characterized nucleus laminaris of the barn owl. We show how the owl's map of ITD can emerge from a combined action of homosynaptic spike-based Hebbian learning and its propagation along the presynaptic axon. In spike-based Hebbian learning, synaptic strengths are modified depending upon the timing of pre- and postsynaptic spikes. A mathematical analysis suggests that both Hebbian learning and its presynaptic propagation are necessary for map formation but the latter can be orders of magnitude weaker than the former. This may be a key mechanism to the formation of computational maps, in particular, when time plays a key role. RK is supported by the DFG, Kl 608/10-1 and Ke 788/1-1. CL holds scholarship of the state of Bavaria.