Cortical processing of visual and tactile stimuli studied by non-invasive rCBF measurements

Blood flow determinations were made in 32 cortical regions of normal subjects during processing of visual and tactile stimuli. One experiment involved eight subjects who were studied during three conditions of visual stimulation achieved by a Spiral-After-Effect (SAE) apparatus: 1. looking at a stationary spiral, 2. a rotating spiral, and 3. performing the SAE test. Average cortical flow increases during these conditions compared to resting were 5%, 7% and 12% respectively. Local activation was seen in occipital, parietal, temporal, and frontal regions. The magnitude and spread of local flow increases were related to task complexity. In another experiment ten subjects were studied during rest and tactile stimulation of the right hand, left hand, and both. The subjects were instructed either to ignore the stimulation (sensation) or to pay attention to it. Sensation was accompanied by parietal and prefrontal flow increases contralateral to side of stimulation. Attention to the right hand mainly enhanced right hemisphere flow, in the same areas as during sensation. Attention to the left hand was associated with large, diffuse flow increases in both hemispheres. The results support recent proposals of right hemisphere dominance for functions related to attention.