Cortical and Callosal Contribution to Sound Localization

The corpus callosum, the principal neocortical commissure, allows for the inter- hemispheric transfer of lateralized information between the hemispheres. It is generally accepted that one of the principal functions of the callosum, at least in the visual and so- matosensory modalities, is to unite the sensory hemispaces for information projecting to different hemispheres (otherwise known as midline fusion). Two of the principal cues to sound localization in free-field are intensity and time differences for sound arriving to the two ears. Since each ear projects in a preponderant manner to the contralateral hemisphere and since complex sounds are generally analyzed at the cortical level, it is possible that the callosum is required to compare time and intensity differences for information arriving in a biased fashion to separate hemispheres. The aim of the present experiments was to examine this problem at the single cell level using cats and at the behavioral level with human subjects having cortical or callosal pathologies.