BINAURAL NOISE STIMULATION OF AUDITORY CALLOSAL FIBERS OF THE CAT - RESPONSES TO INTERAURAL TIME DELAYS

The corpus callosum, the principal neocortical commissure, allows for the interhemispheric transfer of lateralized information between the h emispheres. The aim of the present experiment was to study callosal tr ansfer of auditory information in the cat, with particular reference t o its contribution to sound localization. The corpus callosum was appr oached under direct visual control, and axenic responses were recorded under light anesthesia using glass micro-pipettes. Results showed tha t auditory information is transmitted in the posterior portion of the callosum. Diotic presentations, in which interaural time delay was man ipulated, indicated that, for a large number of fibers, the largest ex citatory or inhibitory interactions were obtained at null interaural t ime delay, a condition which supports the notion of a callosal contrib ution to auditory midline fusion. However, an important number of call osal fibers was also found to be excited maximally at specific, non-ze ro interaural time delays, suggesting that they preferred sounds situa ted at spatial locations other than the midline. The results are discu ssed in relation to those obtained electrophysiologically for the visu al and somesthesic modalities and in terms of results obtained in huma n and animal behavioral experiments.