Learning impairments following selective kainic acid-induced lesions within the neostriatum of rats

In two separate experiments, rats with kainic acid-induced lesions of the anteromedial (AMC) or ventrolateral (VLC) caudate nucleus were compared with controls on various discrete-trial maze and runway tasks: (a) the AMC lesion disrupted the direction but the degree of spontaneous bias in a T-maze, whereas the VLC disrupted the degree of bias but not its direction; (b) the AMC rats were impaired in the acquisition and reversal of a spatial position habit; (c) the VLC rats were impaired in runway extinction; (d) both lesion groups showed enhanced levels of activity when tested under the same conditions of food deprivation, but did not differ from controls when under free-feeding conditions. The histological analysis suggested that kainic acid does permit the selective lesioning of cell bodies in the neostriatum, whilst sparing fibres of passage. It was concluded that the results demonstrate functional heterogeneity within the neostriatum of rats, in direct agreement with the predictions of the 'prefrontal systems' hypothesis of Rosvold [48, 49].