Basal forebrain damage and object-recognition in rats.

Damage to the basal forebrain (BF) produces permanent learning and memory impairments in humans. Most efforts to model these deficits in rats have focused on spatial memory dysfunction; this study was the first to assess the effects of BF damage in rats on the performance of a battery of object-memory tasks commonly employed to assess brain damage-produced amnesia in primates. The performance of rats with bilateral electrolytic lesions of the medial septum and diagonal band (MS/NDB) region of the BF was assessed on three object-memory tasks: nonrecurring items delayed nonmatching-to-sample (DNMS), simple object discrimination, and eight-pair concurrent object discrimination. Lesioned rats and sham-surgery controls were tested on the DNMS task at retention delays of 4, 15, 30, 60 and 120 s both before and after surgery. After surgery, the rats with MS/NDB lesions required significantly more trials than controls to relearn the nonmatching rule; and, once they relearned the rule, they were significantly and comparably impaired at all delays. This impairment did not diminish with either the passage of time or additional practice. In contrast, there were no significant differences between the MS/NDB-lesioned and control groups in the performance of either simple or concurrent object-discrimination tasks. The delay-independent nature of the DNMS deficit and the lack of deficits on the other two object-memory tasks suggest that the effect of the lesion is not the result of an impairment in retention.