ASA 127th Meeting M.I.T. 1994 June 6-10

2aPP21. Neurophysiological studies of acoustic processing in the ventral auditory cortex of the FM bat, Eptesicus fuscus.

Jonathan B. Fritz

James A. Simmons

Dept. of Neurosci., Box 1953, Brown Univ., Providence, RI 02912

A focus of recent experiments on the functional organization of the auditory cortex in the big brown bat has been the characterization of neurons in the newly identified ventral auditory area (VAC). The observations indicate that VAC neurons display significantly higher spontaneous activity, longer response latency and duration than cells in dorsal auditory cortex [Dear et al., J. Neurophysiol. 70, 1988--2009 (1993)]. In VAC there is a higher percentage of physiological cell types whose spectral tuning and echo-delay tuning varies dynamically with stimulus amplitude and context, and cells whose frequency tuning curves are multipeaked. These latter cells may play a functional role in encoding spectral notches in multiple echoes, which are known to carry information about the shape, fine range structure, and textures of a target. Averaged evoked potentials of cells in VAC to tonebursts or FM sweeps show oscillatory responses (150--400 Hz). The role of temporal response patterns in cortical processing of acoustic information will be discussed. The results indicate that the VAC may be a higher auditory processing center. [Work supported by NSF.]