Elucidation of Neural Connectivity between the Upper Limb and the Lower Limb on the Somatosensory Cortex

Abstract

Human whole-body movements require coordination between upper limbs and lower limbs. To achieve interlimb coordination, previous studies have demonstrated that the spinal reflex and the corticospinal excitability of the lower limb were facilitated during upper limb muscle contractions. However, it remains unknown the effect of upper limb muscle contractions on the lower limb area of the somatosensory cortex. The excitability of the somatosensory cortex has been measured using somatosensory evoked potential （SEP） , which is recorded on electroencephalography （EEG） immediately after peripheral electrical stimulation. In this study, we investigated the modulation of SEP following stimulation of the right tibial nerve at the popliteal fossa during wrist flexion. Twelve healthy males participated in the present study. The amplitudes of SEP were compared between relaxing, voluntary wrist flexion, and involuntary wrist flexion induced by neuromuscular electrical stimulation （NMES） to the right median nerve. Voluntary wrist flexion and NMES-induced wrist flexion were matched 10 % of maximal voluntary force （MVF） . The results showed that neither voluntary wrist flexion nor NMES-induced wrist flexion significantly modulated any amplitudes of SEP （i.e., N40, P50, and N70） compared with the rest condition. Our results indicate that wrist flexion has no effect on the lower-limb area of the somatosensory cortex.