Role of cat primary auditory cortex for sound-localization behavior

TLDR

Lesions targeted specific frequency‑band representations in primary auditory cortex guided by physiological mapping, and sound‑localization performance was measured before and after in a free‑field apparatus, including a case of near‑complete unilateral cortical ablation. Lesions of AI produced permanent contralateral deficits for brief tones at the destroyed frequency bands, while other frequencies and long‑duration tones remained normal, showing that AI is both necessary and sufficient for binaural sound‑localization and that location representation is organized by frequency channel.

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.