Hemispheric Asymmetry of Median Nerve Somatosensory Evoked Potential

ABSTRACT

OBJECTIVE: To elucidate interhemispheric asymmetry of the neural generators of somatosensory evoked potential (SEP). METHOD: Median nerve SEP was recorded over 5 sites of each hemisphere in 20 healthy subjects and 23 stroke patients. One electrode was placed over C3'/C4' (position B) and two electrodes were located 2 cm medial (position A) and lateral (position C) to position B, respectively. Additional two electrodes were positioned at 3 cm anterior (position F) and posterior (position P) to position B. The common reference electrode was placed at Fz. RESULTS: In healthy subjects, P22 was more frequently evoked than P27 in position F of the nondominant hemisphere and P27 in position P of the dominant hemisphere. In stroke subjects, fourteen patients demonstrated SEP waveforms over the affected hemisphere. In them, SEP amplitude significantly correlated with proprioception. However, distribution of the recording position showing significant correlation between SEP amplitude and proprioception was different according to dominancy of the affected hemisphere. CONCLUSION: P22 was more dominant in the nondominant hemisphere and P27 in the dominant hemisphere of normal group. Furthermore, clinical correlation of SEP amplitude was affected by the injured hemisphere dominancy in stroke group. These results demonstrate that asymmetry of neural generator distribution can be presumed.