ELECTROPHYSIOLOGICAL STUDIES OF HUMAN-MEMORY

This review summarizes recent experiments that explored human memory processes using recordings of event-related potentials (ERPs) from the brain. In many studies, ERPs elicited by words presented during an acquisition stage have differed as a function of later recall or recognition. These ERP differences, generally in the 400 to 800 ms range, indicate that processes of memory encoding may produce ERP correlates. Numerous studies have also been devoted to ERP effects during recognition. In general, the second presentation of a stimulus was associated with an enhanced positivity relative to the first presentation or to new items. Similar effects have been observed in implicit memory tests in which repetitions were irrelevant to the subject's task. There has been some difficulty in relating these old/new effects to the processes that mediate memory experiences such as recollection and priming. However, a new paradigm that enables a dissociation between ERP correlates of recollection and priming is described. Studies of ERPs recorded from intracranial electrodes have also shown memory sensitivity, particularly for electrode locations near the hippocampus. In summary, ERPs may be useful as indices of both memory encoding and memory retrieval processes.