A functional model of spectral orientation columns in the primary auditory cortex.

Abstract

A functional model of the primary auditory cortex is proposed based on physiological maps of the response area organization in ferret AI [S. A. Shamma, J. W. Fleshman, and P. Wiser, J. Neurophysiol. (submitted for publication)]. Systematic changes in the excitatory and inhibitory portions of the response areas along the isofrequency planes are approximated by a difference of Gaussian function with spatially changing parameters. The fundamental functional principle that emerges from the analysis of the model is that the primary auditory cortex encodes the shape of the acoustic spectrum in the distribution of its responses along the isofrequency planes. Specifically, it maps to each isofrequency plane a normalized measure of the locally averaged gradient of the input spectrum at that frequency. Physiological and psychoacoustical correlates and implications of these findings are explained. Parallels to the functional organization of the visual cortex are also discussed.