SOMATOSENSORY ACTIVATIONS OF THE PARIETAL OPERCULUM OF MAN - A PET STUDY

We tested the hypothesis that somatosensory discrimination of roughnes s (microgeometry) but not of shape (macrogeometry) would activate the parietal operculum (PO) in man. It was also investigated whether a sim ple square pulse indentation of the skin on the index finger would act ivate the PO. Regional cerebral blood flow was measured with [O-15]but anol and positron emission tomography in a total of 20 normal voluntee rs. Ten subjects used their right hand to discriminate objects that di ffered in roughness and similar smooth objects that differed in length . Ten other subjects pressed a button when they felt a square pulse in dentation of the skin on their right index finger in a somatosensory r eaction time task. Discrimination of roughness activated one field in the PO contralaterally and two fields ipsilaterally to the stimulated hand. The discrimination of length activated one field in the PO locat ed ipsilaterally to the stimulated hand. The somatosensory reaction ti me task also activated one contralateral and two ipsilateral fields in the PO, and these fields partially overlapped the activated fields in the roughness discrimination task. Based on the extension of these fi elds and their overlaps we conclude that there exist at least one part of the contralateral PO and at least two parts of the ipsilateral PO that can be activated by somatosensory stimulation of the right hand. We argue further that the contralateral activated part contains a regi on that can be activated by roughness.