Mauthner System Discrimination of Stimulus Direction From the Acceleration and Pressure Components at Sound Onset

ROBERT C. EATON, AUDREY L. GUZIK, AND JANET L. CASAGRAND Ccntc~r,Ji)r Neuroscienw, University of Colorado, Boulder, Colorado 80309-0334 When an animal turns away from an aversive stimu- lus, what are the underlying neurophysiological pro- cesses that extract the correct sensory information and produce an appropriate motor output? The goal of our research program has been to use the Mauthner system as a model neural network to understand such sensori- motor processes (Eaton et al., 199 1). The Mauthner cells are a bilateral pair of brain stem neurons. They receive acoustic and other sensory inputs and connect directly to spinal motoneurons. Together with other reticulospinal cells, the Mauthner cells trigger the C-start, a character- istic escape movement of fishes. This behavior occurs when the animal is presented with a sudden aversive stimulus, such as is produced by a predator during an attack. Previously my laboratory focused on the produc- tion of the escape movement and the role of the Mauthner neurons in organizing the descending flow of motor signals that activate escape. Now, however, we have an excellent idea of other candidate neurons that participate in the escape response (Foreman and Eaton, 1993; Lee et a/., 1993; Fetch0 et al., 1995). To further understand the underlying sensorimotor process, we re- cently began studying how the Mauthner system com- putes the direction of sounds so that the animal makes the correct initial decision to turn left or right away from the stimulus (Eaton et al., 1995a). In this paper we pres-