A ROLE FOR THE HIPPOCAMPAL-FORMATION IN IMPLICIT MEMORY - A 3-D PET STUDY

THE apparent preservation of word priming effects in amnesia has been interpreted as supporting the view that implicit memory depends on bra in systems that are independent of mesial temporal lobe structures whi ch are in part responsible for explicit memory disorders. Nevertheless , a number of studies have demonstrated word priming deficits in amnes ic patients relatively to normal subjects, suggesting that such struct ures may also be involved in implicit memory. To determine whether one such structure, the hippocampal formation, is a component of the brai n system subserving word priming, a 3-D PET study was carried out in 1 3 normal individuals. Encoding was carried out using the brief multipl e presentation technique, a procedure that allows one to effectively c ircumvent contamination of implicit memory tasks by explicit memory st rategies. Results revealed that word priming was indeed associated wit h an activation of the right hippocampal formation. This finding of an hippocampal involvement in word priming calls into question the notio n of absolute dissociability between the brain systems underlying perf ormance on various explicit and implicit memory tasks. (C) 1998 Rapid Science Ltd.