DISTRIBUTION OF CORTICAL ACTIVATION DURING VISUOSPATIAL N-BACK TASKS AS REVEALED BY FUNCTIONAL MAGNETIC-RESONANCE-IMAGING

Human neuroimaging studies conducted during visuospatial working memor y tasks have inconsistently detected activation in the prefrontal cort ical areas depending presumably on the type of memory and control task s employed. We used functional magnetic resonance imaging to study bra in activation related to the performance of a visuospatial n-back task with different memory loads (0-back, 1-back and 2-back tasks). Compar ison of the 2-back versus 0-back tasks revealed consistent, bilateral activation in the medial frontal gyrus (MFG), superior frontal sulcus and adjacent cortical tissue (SFS/SFG) in all subjects and in six out of seven subjects in the intraparietal sulcus (IPS). Activation was al so detected in the inferior frontal gyrus, medially in the superior fr ontal gyrus, precentral gyrus. superior and inferior parietal lobuli. occipital visual association areas, anterior and posterior cingulate a reas and in the insula. Comparison between the 1-back versus 0-back ta sks revealed activation only in a few brain areas. Activation in the M FG. SFS/SFG and IFS appeared dependent on memory load. The results sug gest that the performance of a visuospatial working memory task engage s a network of distributed brain areas and that areas in the dorsal vi sual pathway are engaged in mnemonic processing of visuospatial inform ation.