Hemispheric asymmetry of hand representation in human primary somatosensory cortex and handedness

Objective To evaluate interhemispheric differences of hand representation in primary somatosensory (SI) and motor (MI) cortices and its relation to handedness. Methods MRI-based EEG dipole source analysis was performed separately for early (P14, N20, P22) and middle/late latency (P30, N60, N110) SEP components after left and right median nerve stimulation. In addition, the location of the MI hand area (Ω region) and handedness were determined. Results Equivalent current dipoles (ECDs) of N20, P30 and N60 SEP components were localized in contralateral SI (area 3b, N20 and P30; area 1, N60), the mean P22 ECD localization was in area 4 of contralateral MI. In contrast to the Ω region and the precentral P22 component, ECDs in both areas 3b and 1 were located more laterally in the right than in the left hemisphere. ECDs in the right SI lay more laterally than the ipsilateral Ω region. Asymmetry in SI was not correlated with handedness. Conclusions The data demonstrate that the location of hand representation shows relevant hemispheric asymmetry in human SI, both in areas 3b and 1. Significance Hemispheric asymmetry in SI must be considered in the studies on cortical reorganization and plasticity in SI as well as for transcranial magnetic stimulation (TMS) over SI.