Visual neglect occurs most frequently and persistently after lesions that i
nclude the right supramarginal gyrus (SMG), a part of the inferior parietal
lobule, Patients with this syndrome make very few saccades to the left, an
d show abnormal performance on tasks in which they must covertly shift thei
r attention to the left, suggesting that the right SMG is involved in the g
eneration of saccades and attention shifts, Functional imaging studies of s
accades and covert attention shifts in the normal brain, however, have show
n weak or absent responses in both SMGs, We used event-related functional M
RI to rec examine the responses to saccades and attention shifts within a s
ingle experiment, and to assess responses to left- and right-sided stimuli
independently. When subjects made saccades to peripheral stimuli, the expec
ted responses were seen in striate and prestriate cortex, the superior pari
etal lobules, the frontal eye fields, the supplementary motor area and the
anterior insulae, In addition there was a response in the right SMG but not
in the left SMG, as predicted from the clinical literature. When subjects
made a covert visual assessment of the peripheral stimulus without any sacc
ade, greater activity was seen in all of the areas in the frontoparietal ne
twork, Each area showed a bias towards contralateral stimuli, with two exce
ptions: the anterior insulae gave mainly ipsilateral responses, whilst the
right SMG gave equal responses to right- and left-sided stimuli. These find
ings are discussed in the context of current theories pertaining to the cli
nical syndrome of neglect.