STRATEGIES USED BY HIPPOCAMPAL-LESIONED AND CAUDATE-PUTAMEN-LESIONED RATS IN A LEARNING-TASK

In rats, hippocampal lesions result in impairment of spatial navigatio n, although other learning abilities remain unaltered. When learning a left/right discrimination task, rats can use a spatial strategy (with external maze landmarks-Situation 1) or are forced to use an egocentr ic strategy (without external or internal maze cues-Situation 2). Litt le is known about the extrahippocampal systems involved in the utiliza tion of egocentric strategy. It is suggested that striatum could play an important role in the learning abilities that are spared after hipp ocampal lesion. The aim of our study was to investigate which strategy is used by rats bearing hippocampal or caudate-putamen lesions in the acquisition of a left/right discrimination task in an elevated T-maze in both Situations 1 and 2. We also investigated the effect of each l esion on the reversal of discrimination in both situations. Acquisitio n was not altered in any of the situations; however, a transfer test s howed that hippocampal-lesioned rats used a different strategy (egocen tric) from control animals (spatial) in Situation 1. In addition, reve rsal of the discrimination was impaired in Situation 2. Caudate-putame n lesion produced a transient effect on reversal of discrimination onl y in the egocentric task (Situation 2), but did not impair acquisition of the task in either situation, thus suggesting that the animals wer e able to use either strategy. (C) 1997 Academic Press.