Deficits for representational memory induced by septal and cortical lesions (singly and combined) in rats

A differentiation was made between dispositional memory and representational memory. A delayed-nonmatching-to-sample task in a T-maze operationalized this distinction. Experimental brain lesions in posterior septum and in prelimbic cortex resulted in amnesia for representational memories. The amnesia ameliorated as a function of continued reinforced postoperative testing. When lesions were placed in both structures in the same animals, amnesia for representational memories also occurred, and with further testing, the amnesia ameliorated as indicated by group data. However, examination of the behavioral performance and the lesions in individual animals revealed that when both lesions were adequate, choices remained at chance levels, results suggesting permanent amnesia for representational memories. That the lesion-induced amnesia was restricted to representational memory was indicated by the fact that the rats displayed no amnesia for dispositional memories regarding what to do in the maze. They did not act like naive animals, as they should if they had forgotten the dispositional memories necessary for successful T-maze performance.