Bilateral competitive processing of visual spatial attention in the human brain

Visual spatial attention is an essential brain function that is produced through the interactions of several cortical and subcortical regions. Using the reversible deactivation technique of transcranial magnetic stimulation (TMS) in combination with a visual stimulus detection task, we demonstrated that parietal as well as occipito-parietal cortices in the human brain contribute to spatial attentional behavior. The functional role of left- and right-hemispheric regions appeared to be mirror-symmetric, although the strength of contributions from left and right cortices might differ. Reaction times for baseline and experimental conditions suggested that TMS interfered with an early stage of attentional processing. The experiments also demonstrated an ipsilateral enhancement of spatial attention after unilateral TMS. This observation supports a theoretical model for inter-hemispheric competition in the attentional network.