Right-left asymmetry in tonic pain perception and its modification by simultaneous contralateral noxious stimulation

Administration of the cold pressor test (I test) in normal healthy subjects revealed lateralization of pain perception with the right hand showing higher threshold and tolerance, as well as lower pain scores on Graphic Rating Scale, PPI and MPQ. To find out whether this lateralization persists, the cold pressor test was given while the contralateral hand was simultaneously exposed to non-noxious stimulus (II test) or noxious stimulus (III test). Reversal of laterality to the left hand was observed in the III test in 40% of the subjects for pain threshold. The mechanism of diffuse noxious controls and attentional focus to the noxious stimulus that is more intense, are suggested for the observed changes in laterality when two concurrent noxious stimuli are present.