fMRI activations of SI and SII cortices during tactile stimulation depend on attention.

Somatosensory cortical areas are widely studied with new functional imaging techniques, but usually with poor control over the attentional state of subjects. We applied fMRI to determine possible changes in activations of these areas due to modulations of attention. Attention induced large regional changes, mostly enlargements of activated areas, and more of those at SII than at SI. The number of instances where activation was only seen in attend conditions was also larger at SII than at SI. These results show the importance of controlling the attentional state of the subjects in imaging studies, and give evidence of the different roles of SI and SII cortices in the somatosensory system.