Different cortical activations during visuospatial attention and the intention to perform a saccade.

Everyday life often necessitates dissociation between our directed attention and the intention to direct our gaze. Accordingly, the differential role of visual and motor related areas in the one or the other process is an issue of an ongoing debate. Here we used functional magnetic resonance imaging to elaborate a differentiation between visuospatial attention and the intention for a horizontal saccade in these cortical areas. Subjects fixated a central target, while they directed their attention to a colored cue in the left or right visual field. Regardless of its location, the color of the cue instructed the direction of the upcoming saccade (intention). The attention to the peripheral cue and the intention to perform the saccade were thus either directed to the same side or to opposite sides. A random effects analysis of the imaging data showed that activation of the early visual cortex and the motion sensitive complex was biased by attention to the contralateral cue, whereas activity of the color sensitive complex was modulated by the stimulus instructing a contraversive saccade. The posterior parietal cortex and the proper supplementary eye field (SEF) were most strongly activated in case of spatially congruent attention and intention. In contrast, activity of the pre-SEF and the frontal eye field was enhanced by spatially divergent attention and intention. The results presented here advance our understanding of how the human brain processes spatial information. Noteworthy, the visuomotor related areas show a subtle cortical separation for visual related attention and saccade related intention.