Role of the superior colliculus in analyses of space: Superficial and intermediate layer contributions to visual orienting, auditory orienting, and visuospatial discriminations during unilateral and bilateral deactivations

The superior colliculus (SC) has been implicated in spatial analyses of the environment, although few behavioral studies have explicitly tested this r ole. To test its imputed role in spatial analyses, we used a battery of fou r spatial tasks combined with unilateral and bilateral cooling deactivation of the upper and intermediate layers of the superior colliculus. We tested the abilities of cats to orient to three different stimuli: (1) moving vis ual, (2) stationary visual, (3) stationary white-noise aural. Furthermore, we tested the ability of the cats to discriminate the relative spatial posi tion of a landmark. Unilateral cooling deactivation of the superficial laye rs of the SC induced a profound neglect of both moving and stationary visua l stimuli presented in, and landmark objects located within, the contralate ral hemifield. However, responses to auditory stimuli were unimpaired. Unil ateral cooling deactivation of both the superficial and intermediate layers induced a profound contralateral neglect of the auditory stimulus. Additio nal and equivalent deactivation of the opposite SC largely restored orienti ng to either moving visual or auditory stimuli, and restored landmark posit ion reporting to normal levels. However, during bilateral SC deactivation, orienting to the static visual stimulus was abolished throughout the entire visual field. Overall, unilateral SC deactivation results show that the up per and intermediate layers of the SC contribute in different ways to guidi ng behavioral responses to visual and auditory stimuli cues. Finally, bilat eral superior colliculus deactivations reveal that other structures are suf ficient to support spatial analyses and guide visual behaviors in the absen ce of neural operations in the superior colliculus, but only under certain circumstances. J. Comp. Neurol. 441:44-57,2001. (C) 2001 Wiley-Liss, Inc.