PHYSIOLOGY OF SOMATOSENSORY PERCEPTION - CEREBRAL LATERALIZATION AND EXTINCTION

Objective: To demonstrate the effects of cerebral lateralization and t emporal dynamics on somatosensory perception. Background: We postulate d that perceptual thresholds for simple somatosensory stimuli would be less in the left than the right hand, and that a left/right asymmetry in extinction would exist in healthy right-handed subjects (but not i n left-handed subjects). During the course of these experiments we als o examined the controversy concerning the temporal dynamics of somatos ensory perception. Methods: A total of 126 healthy subjects (age range , 6 to 73 years) participated in the study. Effects of handedness, age , vigilance, gaze, and temporal interval on somatosensory perception w ere examined in a series of experiments. Brief electric pulses were ap plied to the index finger of one or both hands. Results: Perceptual th resholds are lower in the left than the right hand of healthy right-ha nded subjects in a large cohort across a wide age range. Left-handed s ubjects have no overall asymmetry. Even after compensation for baselin e threshold differences, single stimuli in right-handed subjects are p erceived more readily in the left than the right hand, and left-hand t argets are more difficult to mask. Leftward eye/head gaze lowers thres holds in both hands of right-handed subjects (compared with right or s traight gaze). Extinction was consistently maximal when the mask follo wed the target by 50 to 100 msec. Conclusions: The findings demonstrat e clearly that left/right perceptual thresholds for simple somatosenso ry stimuli are asymmetric in healthy right-handed subjects. Both centr al and peripheral asymmetries exist. The central asymmetry and gaze ef fects are consistent with right cerebral dominance for externally dire cted attention. Access of somatosensory stimuli to conscious awareness is delayed and particularly vulnerable to disruption at 50 to 100 mse c after onset of the stimulus.