PARALLEL AND SERIAL PROCESSING OF HAPTIC INFORMATION IN MAN - EFFECTSOF PARIETAL LESIONS ON SENSORIMOTOR HAND FUNCTION

Recent animal studies have shown that there is an evolutionary shift w ithin the order of primates from parallel to serial processing of hapt ic information. In an attempt to determine whether there is also evide nce of serial processing in humans 10 patients with parietal cortical lesions, three patients: with subcortical lesions and one patient afte r hemispherectomy, were examined. Case-by-case and across subject anal ysis of lesion type, sensorimotor profile and electrophysiological fin dings showed that in unihemispheric lesions: (a) there is little impai rment of thermesthesia,nociception and vibration sense; (b) two-point discrimination and integrity of the N20 somatosensory component are hi ghly correlated; (c) a loss of the N20 component is accompanied by a s evere impairment of stereognosis; (d) conversely, in more posterior le sions astereognosis can occur with an intact N20 component; and (e) if the lesion is in the right hemisphere there is frequently impairment of graphesthesia in both hands. These data are taken to indicate seria l processing from SI (as evidenced by an intact N20 component) to post erior parietal cortex allowing progressive spatial and temporal integr ation. In graphesthesia our data suggest an integrative function of th e right parietal cortex for both sides of the body. Other sensory qual ities like vibration nociception and thermesthesia are apparently proc essed in a non-serial, probably parallel way involving both hemisphere s. The effects of cerebral lesions in our series suggest parallel as w ell as serial processing of somesthetic information in man underlying the perception of different haptic features. Copyright (C) 1996 Elsevi er Science Ltd.