Memory and septo-hippocampal connections in rats.

Operated control rats and rats with small lesions in the medial septal region were tested for postoperative retention and transfer learning in a pulse-shaped elevated maze. Both maze problems were, in an empirical sense, spatial. Only when the rats worked on an alteration problem with start box reversals between sessions could the performance be characterized as depending on working memory. It was the working-memory conditions that sustained lesion-induced impairment on the tests of retention and transfer learning, and the lesion-induced behavioral impairment did not ameliorate during the four additional training sessions. Performance on problems that could be solved by reference-memory mechanisms was not impaired by the lesions. The small, but effective, lesions in the medial septal region were presumed to have severed a substantial number of connections comprising the major anterior input from the septum to the hippocampus but to have left intact much of the anterior hippocampal efferents. It is concluded that spatial cognitive mapping is crucially dependent on a basis capability for working memory which, in turn, depends on circuitry involving connections from septal region to hippocampus.