An fMRI study of sex differences in regional activation to a verbal and a spatial task

Sex differences in cognitive performance have been documented, women perfor ming better on some phonological tasks and men on spatial tasks. An earlier fMRI study suggested sex differences in distributed brain activation durin g phonological processing, with bilateral activation seen in women while me n showed primarily left-lateralized activation. This blood oxygen level-dep endent fMRI study examined sex differences (14 men, 13 women) in activation for a spatial task (judgment of line orientation) compared to a verbal-rea soning task (analogies) that does not typically show sex differences. Task difficulty was manipulated. Hypothesized ROI-based analysis documented the expected left-lateralized changes for the verbal task in the inferior parie tal and planum temporale regions in both men and women, but only men showed right-lateralized increase for the spatial task in these regions. Image-ba sed analysis revealed a distributed network of cortical regions activated b y the tasks, which consisted of the lateral frontal, medial frontal, mid-te mporal, occipitoparietal, and occipital regions. The activation was more le ft lateralized for the verbal and more right for the spatial tasks, but men also showed some left activation for the spatial task, which was nor seen in women. Increased task difficulty produced more distributed activation fo r the verbal and more circumscribed activation for the spatial task. The re sults suggest that failure to activate the appropriate hemisphere in region s directly involved in task performance may explain certain sex differences in performance. They also extend, for a spatial task, the principle that b ilateral activation in a distributed cognitive system underlies sex differe nces in performance. (C) 2000 Academic Press.