A large-scale distributed network for covert spatial attention - Further anatomical delineation based on stringent behavioural and cognitive controls

Functional MRI was used to examine cerebral activations in 12 subjects whil e they performed a spatial attention task. This study applied more stringen t behavioural and cognitive controls than previously used for similar exper iments: (i) subjects were included only if they showed evidence of attentio nal shifts while performing the task in the magnet; (ii) the experimental t ask and baseline condition were designed to eliminate the contributions of motor output, visual fixation, inhibition of eye movements, working memory and the conditional (no-go) component of responding, Activations were seen in all three hypothesized cortical epicentres forming a network for spatial attention: the lateral premotor cortex (frontal eye fields), the posterior parietal cortex and the cingulate cortex, Subcortical activations were see n in the basal ganglia and the thalamus, Although the task required attenti on to be equally shifted to the left and to the right, eight of 10 subjects showed a greater area of activation in the right parietal cortex, consiste nt with the specialization of the right hemisphere for spatial attention, O ther areas of significant activation included the posterior temporo-occipit al cortex and the anterior insula, The temporo-occipital activation was wit hin a region broadly defined as MT+ (where MT is the middle temporal area) which contains the human equivalent of area MT in the macaque monkey, This temporo-occipital area appears to constitute a major component of the funct ional network activated by this spatial attention task, Its activation may reflect the 'inferred' shift of the attentional focus across the visual sce ne.