Role of Primary Auditory Cortex in Acoustic Orientation and Approach-to-Target Responses

The role of the primary auditory cortex in acoustic orientation and sound localization was explored by measuring the accuracy with which ferrets turned toward and approached the source of broadband sounds in the horizontal plane. In two animal groups trained by positive conditioning to perform this task, we either made small, bilateral aspiration lesions in the middle ectosylvian gyrus, where the primary auditory cortex is located, or implanted over it a polymer that released over a period of several weeks the GABAA agonist muscimol to silence the underlying cortex. Neither aspiration nor inactivation of the primary auditory cortex prevented the animals from orienting toward or approaching the source of the sound, but did produce a modest deficit in performance, as reflected by a reduction in accuracy in the localization of brief sounds (40-200 ms), especially for lateral locations. The accuracy of orienting responses was essentially unaltered, and only a small increase in variability for lateral sound locations was observed for short-duration stimuli. The close similarity in the behavioral responses observed after each manipulation suggests that these results reflect the true contribution of the primary auditory cortex to auditory localization. Given the modest nature of the observed deficits, our findings further suggest that additional areas within the auditory cortex must be also involved in spatial hearing.