EFFECTS OF LESIONS OF DIFFERENT PARTS OF THE SEPTOHIPPOCAMPAL SYSTEM IN PRIMATES ON LEARNING AND RETENTION OF INFORMATION ACQUIRED BEFORE OR AFTER SURGERY

Data from a large series of experiments on marmosets with lesions of t he septal/diagonal band area (DBP, fornix or CA1 area of the hippocamp us are analysed in terms of retention of information learned before su rgery, acquisition of new information and retention of information acq uired after surgery. It is shown that although all three lesions impai r acquisition of a specific type of new information, lesions of CA1 re sult in a severe retrograde amnesia but no forgetting of that type of information adequately acquired after surgery, whereas lesions of the DB do not cause retrograde amnesia but do result in significant forget ting, Monkeys with fornix transection occupied an intermediate positio n in their pattern of learning impairments; some animals showed eviden ce of forgetting, whereas the great majority showed retrograde amnesia . These data may be relevant to an understanding of the different exte nt of amnesia in patients with different pathology within the medial t emporal lobe and associated subcortical structures.