A PET Study of Visual-tactile Sensory Integration in Man

Abstract:
We have extended our previous PET study of visual-tactile integration [Banati et al. Neuropsychologia 38:115-124] by using (a) a modified version of the arc-circle test (b) a PET camera with wider axial field of view, (c) reducing putative attentional load by including a learning procedure. The test required subjects (n=8) to compare touched metal arcs with viewed circles and arcs on a computer screen in three different test conditions: one cross-modal (Touch-Vision) and two intra-modal (TT/VV). Regional cerebral blood flow was measured using the water bolus method with the Seimens/CTI EXACT 966 PET camera and analysed using SPM99. The VV-TV comparison replicated our previous findings of bilateral visual cortex activation. TV-VV revealed activations in left BA40 as reported previously and activations in left BA3 and right cerebellum in the extended axial view. TT-TV significantly activated right BA6 and right BA1/3. TV-TT revealed bilateral activations in BA18/19 and left BA40 more posterior to that in the TV-VV contrast. Unlike our previous study we did not identify activations in the anterior cingulate and DLPFC during cross-modal matching, perhaps due to the pre-scan training shown by improved and stable task performance. These findings suggest modulation of activity in primary sensory areas is specifically important in visual-tactile matching, possibly via selective attention as evidenced by activations seen in the parietal lobes.