We have identified a limited region in the posterior, but not anterior, half of the cat's middle suprasyl-vian region which, when cooled and inactivated unilaterally, results in a profound visual neglect of stimuli introduced into the contracooled hemifield. The severity of the deficit matches that induced by unilateral cooling of the superior colliculus. The cortical region is located at the temporo-occipito-parietal junction and is believed to be equivalent to a region centered on or close to the area V5 complex of primates. Following unilateral damage of cortex at the temporo-occipito-parietal (TOP) junction, humans fail to either notice or orient toward stimuli that appear in visual space contralat-eral to the lesion (1-5). Similar visual deficits have been obtained following restricted unilateral lesions that include all or part of the TOP cortex in monkeys (6-8). In the present study, we have produced a similar neural deficit in cats by unilaterally cooling, and deactivating a region within the TOP cortex. Moreover, we show that a deficit of equivalent magnitude is produced by unilaterally deactivating the superficial and intermediate layers of the superior colliculus (SC). The broad similarity of these results suggests that both TOP cortex and SC play important roles in redirecting attention to new locations in the visual field. Moreover, the cooling-induced-and lesion-induced-neglect in cats, monkeys, and humans suggests that there are largely equivalent, functionally homol-ogous circuits in all three species that likely include the SC. EXPERIMENTAL METHODS Cooling probe loops, fashioned out of hypodermic tubing (9), were implanted unilaterally into the lumen of the middle suprasylvian (MS) sulcus of five cats and bilaterally in another three cats for a total of 11 probes. Each probe was in contact, on the medial side, with the middle suprasylvian gyrus (mssg) and, on the lateral side, with the middle ectosylvian gyrus (ME). In five of the hemispheres arrays of miniature thermo-couples (Omega Engineering, Stamford, CT) were chronically implanted in cortex adjacent to the probes to measure temperatures. Four cooling probes were also implanted in contact with the SC of three cats. In these cats, the posterior 3-4 mm of the corpus callosum was severed to facilitate retraction of the cerebral hemisphere to permit visualization and accurate placement of the probe in contact with the SC. In these cats, temperature measurements were made in an acute procedure at the end of behavioral testing. All surgical procedures were carried out in accordance with Belgian and United States governmental guidelines and regulations. Perimetry. Orienting behavior was examined in a perimetry arena which consists of a series of openings around the The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. periphery of the arena for the introduction of stimuli and rewards from below...
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