THE ROLE OF ANTERIOR ECTOSYLVIAN CORTEX IN CROSS-MODALITY ORIENTATIONAND APPROACH BEHAVIOR

Physiological and behavioral studies in cat have shown that corticotec tal influences play important roles in the information-processing capa bilities of superior colliculus (SC) neurons. While corticotectal inpu ts from the anterior ectosylvian sulcus (AES) play a comparatively sma ll role in the unimodal responses of SC neurons, they are particularly important in rendering these neurons capable of integrating informati on from different sensory modalities (e.g., visual and auditory). The present experiments examined the behavioral consequences of depriving SC neurons of AES inputs, and thereby compromising their ability to in tegrate visual and auditory information. Selective deactivation of a v ariety of other cortical areas (posterolateral lateral suprasylvian co rtex, PLLS; primary auditory cortex, AI, or primary visual cortex, 17/ 18) served as controls. Cats were trained in a perimetry device to ign ore a brief, low-intensity auditory stimulus but to orient toward and approach a near-threshold visual stimulus (a light-emitting diode, LED ) to obtain food. The LED was presented at different eccentricities ei ther alone (unimodal) or combined with the auditory stimulus (multisen sory). Subsequent deactivation of the AES, with focal injections of a local anesthetic, had no effect on responses to unimodal cues regardle ss of their location. However, it profoundly, though reversibly, alter ed orientation and approach to multisensory stimuli in contralateral s pace. The characteristic enhancement of these responses observed when an auditory cue was presented in spatial correspondence with the visua l stimulus was significantly degraded. Similarly, the inhibitory effec t of a spatially disparate auditory cue was significantly ameliorated, The observed effects were specific to AES deactivation, as similar ef fects were not obtained with deactivation of PLLS, AI or 17/18, or sal ine injections into the AES. These observations are consistent with po stulates that specific cortical-midbrain interactions are essential fo r the synthesis of multisensory information in the SC, and fur the ori entation and localization behaviors that depend on this synthesis.