Dynamic spatial coding within the dorsal frontoparietal network during a visual search task.

To what extent are the left and right visual hemifields spatially
coded in the dorsal frontoparietal attention network? In many
experiments with neglect patients, the left hemisphere shows a
contralateral hemifield preference, whereas the right hemisphere
represents both hemifields. This pattern of spatial coding is often
used to explain the right-hemispheric dominance of lesions causing
hemispatial neglect. However, pathophysiological mechanisms of
hemispatial neglect are controversial because recent experiments on
healthy subjects produced conflicting results regarding the spatial
coding of visual hemifields. We used an fMRI paradigm that allowed
us to distinguish two attentional subprocesses during a visual
search task. Either within the left or right hemifield subjects
first attended to stationary locations (spatial orienting) and then
shifted their attentional focus to search for a target line.
Dynamic changes in spatial coding of the left and right hemifields
were observed within subregions of the dorsal front-parietal
network: During stationary spatial orienting, we found the
well-known spatial pattern described above, with a bilateral
hemifield representation in the right hemisphere and a
contralateral preference in the left hemisphere. However, during
search, the right hemisphere had a contralateral preference and the
left hemisphere equally represented both hemifields. This finding
leads to novel perspectives regarding models of visuospatial
attention and hemispatial neglect.