P3 components evoked by unilateral and bilateral somatosensory stimulation: normative data for the study of neglect syndrome

Latency and amplitude of an "odd-ball" somatosensory P3 component evoked either by unilateral or bilateral somatosensory target stimulation, were measured in 15 healthy right-handed subjects (age range 42-79 years) in order to obtain normative data useful for studying the neglect syndrome. The bilateral stimulation protocol was designed to investigate the tactile extinction phenomenon. P3 waves were recorded from nine electrodes. A three-way Anova showed that mean P3 latency on the whole scalp following unilateral stimulations, regardless of side (i.e. right or left stimulations), was significantly longer than that observed after bilateral stimulation. Both "early" and "late" peaks were usually observed in P3 complex. The bilateral modality stimulation showed a more evident "early" peak than the two unilateral stimulations. No significant mean P3 amplitude differences were observed on the whole scalp between bilateral and unilateral stimulations. No significant amplitude differences were observed either for the right or the left hemisphere. The reported latency decrease in the bilateral target stimulation may be a valuable cue for studying possible modifications in patients affected by neglect.