EVIDENCE FOR A SPECIFIC INFORMATION-PROCESSING DEFICIT IN MONKEYS WITH LESIONS OF THE SEPTOHIPPOCAMPAL SYSTEM

Monkeys with dysfunction of the septo-hippocampal system induced by ex citotoxic lesion of the CA1 region of the hippocampus, or the septal/d iagonal band area (which sends cholinergic projections to the hippocam pus via the fornix), or with fornix transection were impaired on condi tional learning tasks (when X choose A not B, when Y choose B not A) w hen trials with these different contingencies were presented in pseudo random order but they were not impaired on learning this type of task if, prior to learning with trials in the pseudorandom order, the two t ypes of trial had been presented in a fixed number of alternating batc hes of each type of trial. These results suggest that the septo-hippoc ampal system is required to process information in a particular type o f way rather than to process a particular type of information and supp orts the view that the amnesia which results from medial temporal lobe damage in humans comprises an impairment of encoding information into long-term memory.