A model of the primary auditory cortex response to sequences of pure tones

Abstract

The neurons in the primary auditory cortex (A1) are una-ble to sustain responses to sequences of stimuli presentedat rates exceeding approximately 20 Hz. The ventralmedial geniculate body, which provides the main input toA1, is in contrast able to respond to sequences with ratesupward of 200 Hz. This filtering of periodic stimuli hasbeen attributed to thalamocortical synaptic depression[1,2]. However, there also exists a frequency-selective fil-tering below 20 Hz known as differential suppression[3,4]. Such filtering produces a receptive field refinementin A1 neurons, rendering them more selective to the fre-quency of presented tones as the presentation rate isincreased.This phenomenon is thought to play a fundamental rolein auditory grouping (or auditory stream segregation,known as auditory streaming) phenomena, organizingsequential sounds into perceptual streams, reflecting dis-tinct ambient sound sources [5]. Here we propose a sim-ple model of A1 that can account for the differentialsuppression phenomenon. Our model has constraintscompatible with recent physiological findings in A1, suchas the approximate balance of inhibition and excitation[6,7], the presence of thalamocortical synaptic depression[1], and the role of intracortical and thalamocortical syn-apses in the formation of A1's activity pattern [8].