Role of Somatosensory Cortex in Visuospatial Attention

The human somatosensory cortex (S1) is not among the brain areas usually associated with visuospatial attention. However, such a function can be presumed, given the recently identified eye proprioceptive input to S1 and the established links between gaze and attention. Here we investigated a rare patient with a focal lesion of the right postcentral gyrus that interferes with the processing of eye proprioception without affecting the ability to locate visual objects relative to her body or to execute eye movements. As a behavioral measure of spatial attention, we recorded fixation time during visual search and reaction time for visual discrimination in lateral displays. In contrast to a group of age-matched controls, the patient showed a gradient in looking time and in visual sensitivity toward the midline. Because an attention bias in the opposite direction, toward the ipsilesional space, occurs in patients with spatial neglect, in a second study, we asked whether the incidental coinjury of S1 together with the neglect-typical perisylvian lesion leads to a milder neglect. A voxelwise lesion behavior mapping analysis of a group of right-hemisphere stroke patients supported this hypothesis. The effect of an isolated S1 lesion on visual exploration and visual sensitivity as well as the modulatory role of S1 in spatial neglect suggest a role of this area in visuospatial attention. We hypothesize that the proprioceptive gaze signal in S1, although playing only a minor role in locating visual objects relative to the body, affects the allocation of attention in the visual space.