PET studies of somatosensory processing of light touch

The studies discussed in this report investigate the neural mechanisms involved in processing a light tactile stimulus as measured by positron emission tomography (PET). This light tactile stimulus (a 2-Hz tap with a von Frey hair) produced a significant increase in regional cerebral blood flow (rCBF) in contralateral primary somatosensory cortex (SI) and bilateral secondary somatosensory cortex (SII), with a larger response in the side contralateral to the stimulus. Light tactile stimulation also produced activity in multiple discrete areas in the human inferior parietal lobule (IPL), which we believe to comprise a region homologous to the monkey area 7b or feline tertiary somatosensory cortex (SIII). Directing attention to the tactile stimulus increased blood flow to SIII and activated a right-lateralized cortical network, regardless of the side of body stimulated. Directed attention to the stimulus decreased blood flow to visual cortex, but minimally modulated SI rCBF.