Role of cat primary auditory cortex for sound-localization behavior

Abstract

Small lesions designed to completely destroy the cortical zone of representation of a restricted band of frequency were introduced within the primary auditory cortex (AI) in adult cats. Physiological mapping was used to guide placement of lesions. Sound-localization performance was evaluated prior to and after induction of these lesions in a seven-choice free-sound-field apparatus. All tested cats had profound contralateral hemifield deficits for the localization of brief tones at frequencies roughly corresponding to those whose representations were destroyed by the lesion. Sound-localization performance was normal at all other test frequencies. In a single adult cat, a massive lesion destroyed nearly all auditory cortex unilaterally, with only the representation of a narrow band of frequency within AI spared by the lesion. This cat had normal abilities for azimuthal sound localization across that frequency band but a profound contralateral deficit for the azimuthal localization of brief sounds at all other frequencies. Recorded sound-localization deficits were permanent. Localization of long-duration tones was not affected by a unilateral AI lesion. These studies indicate that, at least in cats, AI is necessary for normal binaural sound-localization behavior; among auditory cortical fields, AI is sufficient for normal binaural sound-localization behavior; sound-location representation is organized by frequency channel in the auditory forebrain; and AI in each hemisphere contributes to only contralateral free-sound-field location representation.