Directional Hearing by the Mauthner System

Eaton E. P. O. Biology University of Colorado Boulder, Co. 80309 Abstract We provide a computational description of the function of the Mauthner system.This is the brainstem circuit which initiates faststart escapes in teleost fish in response to sounds. Our simulations, usingbackpropagation in a realistically constrained feedforward network, have generated hypotheses which are directly interpretable interms of the activity of the auditory nerve fibers, the principle cells of the system and their associated inhibitory neurons. 1 INTRODUCTION 1.1 THE M.AUTHNER SYSTEM Much is known about the brainstem system that controls fast-start escapes in teleost fish. The most prominent feature of this network is the pair of large Mauthner cells whose axons cross the midline and descend down the spinal cord to synapse on primary motoneurons. The Mauthner system also includes inhibitory neurons, the PHP cells, which have a unique and intense field effect inhibition at the spikeinitiating zoneof the Mauthner cells (Faber and Korn, 1978). The Mauthner system is part of the full brainstem escape network which also includes two pairs of cells homologous to the Mauthner cell and other populations of reticulospinal neurons. With this network fish initiate escapes only from appropriate stimuli, turn away from the offending stimulus, and do so very rapidly with a latency around 15 msec in goldfish.