Multimodal mechanisms of attention related to rates of spatial shifting in vision and touch.

Covert attention can be directed spatially in several different sensory modalities (e.g. vision and touch). Recent psychological experiments indicate the existence of crossmodal links in spatial attention, but their neural basis in humans remains underspecified. We used positron emission tomography (PET) to assess the role of stimulus modality in the activity of brain regions involved in different rates of spatial attention shifting. A 2 x 2 factorial design manipulated the rate (high versus low) of spatial attention shifts between left and right hemifields, plus the sensory modality (vision versus touch) of stimulation. Two brain regions showed activations related to attentional shift-rate, independent of the stimulated modality: these were the right frontopolar gyrus, and the right posterior superior temporal sulcus (STS). The anterior area showed higher blood flow with the high rate of shifts in spatial attention, while the posterior area showed higher flow during the low rate conditions, where attention was sustained for longer on one side. No area showed a significant rate effect in one modality without an effect in the second modality. These results demonstrate multimodal roles for the activated brain regions in relation to the rate of spatial attention shifting, plus right-hemisphere dominance for this. They also suggest that anterior and posterior regions of the spatial-attention network play different roles in attention shifting.