Brain activity during the encoding, retention, and retrieval of stimulus representations

Studies of delayed nonmatching-to-sample (DNMS) performance following lesio ns of the monkey cortex have revealed a critical circuit of brain regions i nvolved in forming memories and retaining and retrieving stimulus represent ations. Using event-related functional magnetic resonance imaging (fMRI), w e measured brain activity in 10 healthy human participants during performan ce of a trial-unique visual DNMS task using novel barcode stimuli. The even t-related design enabled the identification of activity during the differen t phases of the task (encoding, retention, and retrieval). Several brain re gions identified by monkey studies as being important for successful DNMS p erformance showed selective activity during the different phases, including the mediodorsal thalamic nucleus (encoding), ventrolateral prefrontal cort ex (retention), and perirhinal cortex (retrieval). Regions showing sustaine d activity within trials included the ventromedial and dorsal prefrontal co rtices and occipital cortex. The present study shows the utility of investi gating performance on tasks derived from animal models to assist in the ide ntification of brain regions involved in human recognition memory.