Abstract

A fundamental function that the auditory system must perform is the determination of the spatial location of a sound source. In this set of experiments, behavioral and reversible deactivation techniques were used to examine the contributions that specific regions of auditory cortex made to the spatial localization of an acoustic stimulus. All of the experiments were conducted using adult, intact cats that received one or two bilateral pairs of cooling loops over discrete regions of auditory cortex. In the first set of experiments the contributions of individual regions of cat auditory cortex to sound localization during bilateral and unilateral deactivation were examined. Orienting to an acoustic stimulus was used as a behavioral index and performance was examined before, during, and after both unilateral and bilateral reversible cooling deactivation of each locus. Overall, when deactivated, areas AI (primary auditory cortex)/dorsal zone of auditory cortex (DZ), anterior ectosylvian sulcus (AES) or the posterior auditory field (PAF) all produce sound localization deficits. Furthermore, recent studies have identified that neurons in DZ have a high degree of spatial tuning. Therefore, the second set of experiments examined the dissociation of the roles of AI and DZ in the localization of sound. The results suggested that DZ is a separate and independent area from AI and is also critical for sound localization. Finally, compelling data indicates that there is a “division of labor” in auditory cortex allowing for separate processing of patterned or spatially-oriented stimuli. Therefore, the last set of experiments examined the dissociation of acoustic pattern processing and acoustic spatial localization in non-primary auditory cortex. Cats were trained to accurately localize the spatial position of a broad-band noise burst or to discriminate between different temporal patterns of acoustic stimuli of the same temporal duration. The results showed a clear double dissociation between pattern and spatial processing and provided critical evidence in support of the possible existence of “what” and “where” processing streams in auditory cortex.