Dissociation of memory retrieval and search processes: An event-related fMRI study

A cognitive task can often be subdivided into several subprocesses, which f ollow a specific temporal order. Here, we report an event-related functiona l magnetic resonance imaging (fMRI) experiment on memory search, in which t he temporal onset of search in primary memory was varied relative to retrie val from secondary memory. Furthermore, previous behavioral studies demonst rated that search times in primary memory depend on the number of items in a memory set, whereas retrieval from secondary memory is a set-size indepen dent process. We analyzed the dependency of the blood oxygenation level dep endent (SOLD)-response on the temporal onset of memory search on the one ha nd and on memory set size on the other hand to differentiate the contributi on of retrieval from secondary memory, maintenance in primary memory, item search in primary memory, and response-related processes. The timing of act ivation followed cue presentation bilaterally in the middle frontal gyri (B rodmann area (BA) 9,46) and the inferior parts of the precentral gyri (BA6) . in all other regions of interest (ROI), supplementary motor area (SMA), p osterior parietal cortex, antero-superior insula, and primary motor cortex, the onset of activation was delayed with delayed probe presentation, rulin g out participation in retrieval from secondary memory. The amplitude of th e BOLD-response increased with increasing memory set size in all ROI except primary motor cortex and left posterior parietal cortex. All areas with cu e-associated BOLD onset, suggesting involvement in retrieval, showed prolon ged BOLD activation, suggesting that they also support maintenance of the r etrieved information. Microsc. Res. Tech. 51:29-38, 2000. (C) 2000 Wiley-Li ss, Inc.