BLOOD-FLOW CHANGES IN HUMAN SOMATOSENSORY CORTEX DURING ANTICIPATED STIMULATION

POSITRON emission tomography (PET) measurements of brain blood flow we re used to monitor changes in the human primary and secondary somatose nsory cortices during the period when somatosensory stimuli were expec ted. In anticipation of either focal or innocuous touching, or localiz ed, painful shocks, blood flow decreased in parts of the primary somat osensory cortex map located outside the representation of the skin are a that was the target of the expected stimulus. Specifically, attendin g to an impending stimulus to the fingers produced a significant decre ase in blood flow in the somatosensory zones for the face, whereas att ending to stimulation of the toe produced decreases in the zones for t he fingers and face. Decreases were more prominent in the side ipsilat eral to the location of the expected stimulus. No significant changes in blood flow occurred in the region of the cortex representing the sk in locus of the awaited stimulation. These results are concurrent with a model of spatial attention in which potential signal enhancement ma y rely on, generalized suppression of background activity(1).