The neural mechanism for directional escape in the goldfish

Abstract

In response to sudden sound, many fishes rapidly accelerate away from the stimulus. This complex behavior, or C-start, is mediated by a network of brain-stem neurons that receive acoustic input and connect to motoneurons in the spinal cord. In the brain-stem network, the bilateral pair of Mauthner cells (M-cells) play the major role in determining the initial direction of the C-start. Each M-cell axon crosses the brain and connects to motoneurons on the opposite side of the body, so that the animal turns away from the side of the activated M-cell. M-cells receive primary acoustic afferents and inhibitory input from a network of ‘‘PHP’’ cells. PHP cells have a very short latency response to sound and operate in a feedforward mode to regulate M-cell firing threshold. These studies suggest that the PHP cells receive specific combinations of pressure- and displacement-sensitive auditory afferents that inhibit the M-cell to sounds coming from the side of the body opposite the stimulus. Thus only the correct M-cell fires, while its opposite counterpart is inhibited by PHP cells. Present studies involve an electrophysiological, behavioral, and neurocomputational analysis of this hypothesis. [Work supported by NIH and ONR.]