DEFICITS IN VISUAL-DISCRIMINATION PERFORMANCE FOLLOWING NEGLECT-PRODUCING UNILATERAL LATERAL HYPOTHALAMIC-LESIONS IN THE ALBINO-RAT

Adult male albino rats were trained with water reinforcement on a lateralized visual discrimination task. For 6 rats the correct head turn-nose poke response was to the same side as the discriminative stimulus (turn towards group). For 6 others the correct response was to the side opposite from the discriminative stimulus (turn away group). Immediately after a rat had mastered its task, a unilateral electrolytic lesion was made under ether anesthesia through a stainless steel electrode previously implanted in the lateral hypothalamus (LH). Discrimination training continued until the rat''s performance returned to criterion. The lesions produced contralateral neglect as demonstrated by deficits in turning and orientation contratlateral to the lesion. The lesions also disrupted all measures of discrimination performance (per cent correct, latency and duration of observing response) for trials on which responses contralateral to the lesion were correct, regardless of whether the discriminative stimulus was also contralateral (turn towards group) or was ipsilateral (turn away group). These data are interpreted as showing that contralateral neglect following LH lesions is associated with a deficit in initiating instrumental responses contralateral to the lesion. They also confirm previous results from a similar task using tactile discriminative stimuli.