The zona incerta is known to receive a contingent of fibers from the occipital cortex. To test whether this subthalamic region plays a differential role in visually guided behavior, adult albino rats, trained on both a visual pattern discrimination problem and an equally difficult nonvisual (incline plane) discrimination problem, sustained lesions to the zona incerta and were subsequently tested for retention. Significant retention deficits were observed only on the visual problem. These results suggest that the occipitoincertal pathway is selectively involved in visually guided behavior.

Discrete bilateral electrolytic lesions destroying the posterior division of the caudoputamen (disconnecting the occipito-striate projection) produces moderate losses in retention of a horizontal-vertical discrimination habit in the rat. Similarly placed lesions had a significantly smaller effect on an equally difficult nonvisual discrimination habit. These results, in conjunction with others, suggest that multiple occipitofugal systems are involved in visually guided behavior. Webster (1961) has demonstrated that the projection of virtually all cortical areas upon the caudoputamen (CP) is organized on a topographical basis in the rat. With respect to the rostral-caudal dimension, for example, the anterior cortical regions project to the anterior portions of the CP, while the posterior cortical regions give rise to projections to the posterior portions of the CPo That a cortico-striate pathway may playa significant role in visually guided behavior was first suggested by the finding that lesions to the tail of the caudate nucleus impair visual discrimination learning in monkeys (Divac, Rosvold, & Szwarcbart, 1967). More recently , Livesey and Muter (1976) , using the method of electrical (blocking) stimulation, have reported retardation in visual discrimination reversal in rats stimulated within the posteroventral CP.The purpose of the present study was to determine if lesions to the posterior aspect of the CP in rats would produce a selective deleterious effect on a visual discrimination habit. MEmODAdult male albino rats of the Wistar strain were trained to approach a horizontal black-and-white striped card (positive) and to avoid an adjacent vertical black-and-white striped card (negative) in a Thompson-Bryant (1955) discrimination apparatus . Under the motive of escape-avoidance of footshock , a response to the unlocked positive card admitted the animal to the goalbox, whereas a response to the locked negative card was automatically punished by mild footshock . The positive card was switched from the left to the right window in a strict double-alternation sequence. Eight trials were given daily with an intertrial interval of 60 sec. The criterion of learning consisted of no more than one error in 2 consecutive days . Following learning, the majority of rats sustained one-stage bilateral electrolytic lesions to the posterior aspect of the CP; the remaining rats served as the normal control group . After a recovery (or rest) period of 10 days, the animals were given a Reprint requests should be sent to Robert Thompson ,