A Developmental Learning Rule for Coincidence Tuning in the Barn Owl Auditory System

Abstract

Binaural coincidence detection is essential for the localization of external sounds and requires auditory signal processing with high temporal precision. We present an integrateand-fire model of spike processing in the third order nucleus laminaris of the auditory pathway of the barn owl. Each input spike generates an excitatory postsynaptic potential with a width of 250 ?s. Output spikes occur with a tenfold enhanced temporal precision. This is possible since neuronal connections are fine tuned during a critical period of development as has been suggested by recent experiments. This rule does not only explain the temporal presicion in the output, but causes also a tuning to interaural time difference. The learning rule is of the Hebbian type: A synaptic weight is increased if a presynaptic spike arrives at about the same time as or slightly before postsynaptic firing. A presynaptic spike arriving after postsynaptic firing leads to a decrease of the synaptic efficacy.