Effects of selective excitotoxic prefrontal lesions on acquisition of nonmatching- and matching-to-place in the T-maze in the rat: differential involvement of the prelimbic-infralimbic and anterior cingulate cortices in providing behavioural flexibility

The present study investigated the contributions of the medial prefrontal c ortex and its major subdivisions, the dorsal anterior cingulate (ACd) and p relimbic-infralimbic (PL) cortices, to spatial working memory and inhibitor y control processes. In experiment 1, excitotoxic lesions centred in the AC d or PL cortex did not affect acquisition of a nonmatching-to-place task in the T-maze with a retention interval of 10 s. However, the same reinforced alternation task was impaired by larger prefrontal lesions that combined A Cd and PL cortices. In experiment 2, new animals were trained on a matching -to-place task in the T-maze that uses a rule counter to the animals' innat e bias to alternate spontaneously. Now, discrete lesions of both the ACd an d PL cortices impaired acquisition, but in different ways. Both animals wit h PL and with ACd lesions perseverated by nonmatching for more sessions tha n the controls, but only the PL animals also showed a more general increase in perseveration reflected in a further, extended period of applying an in efficient response rule (e.g. always turn right) and a deficit at reversing from matching to nonmatching. Acquisition of the matching-to-place task wa s also impaired by combined lesions of ACd and PL cortices. Overall, whilst spatial working memory processes appear to remain intact in those animals with discrete prefrontal lesions, the present findings provide strong evide nce for the differential involvement of the prelimbic-infralimbic and anter ior cingulate regions in providing behavioural flexibility.