THE ROLE OF THE CAT’S ANTERIOR ECTOSYLVIAN CORTEX IN

Abstract

Behavioral studies have revealed that regions along the anterior ectosylvian sulcus (AES) of the cat cortex are critical for orientation to multisensory stimuli. However, whether AES also plays a role in orientation to unisensory auditory stimuli is not yet clear. Some studies have shown that AES deactivation does not produce unisensory (visual or auditory) orientation deficits, consistent with physiological studies in the superior colliculus. More recently, however, AES deactivation has been shown to have a significant negative impact on sound localization. It is unknown why such similar studies show such different results. We hypothesized that the differences in auditory orientation behaviors following AES deactivation may be related to differences in the spectral characteristics of the auditory stimuli used in these experiments. To test this notion, we employed an auditory orientation task using two distinct auditory test stimuli that would mimic, in part, those used previously. Thus, cats were trained to orient to both broadband (200-20,000 Hz) and low (800-5000 Hz) frequency noise pulses, and their auditory localization capabilities were evaluated following unilateral AES lesions. To determine if AES lesions also effected movements to unisensory visual stimuli, cats also were trained in a standard visual orientation task. During the first post-lesion week, AES lesioned animals failed to orient to both vi broadband and low frequency auditory stimuli presented in the contralesional auditory field, except for occasional movements to stimuli in the more central target locations. Orientation in ipsilesional auditory space was unaffected. By the second post lesion week, however, orientation to broadband stimuli began to improve in a central to peripheral fashion. By the third week post-lesion, orientation to broadband stimuli was back at pre-lesion values. In contrast, the accuracy of orientation to low frequency stimuli remained substantially impaired. These same lesions had no effect on contralesional visual orientation behaviors other than a transient 1-2 day impairment. These data reveal that lesions of the caudal AES, that presumably disrupt both it auditory and visual subdivisions, produce enduring deficits in an animal's ability to accurately orient to low frequency but not broadband noise pulses. They also show that visual orientation is unaffected by such lesions.