High-frequency transcutaneous electrical nerve stimulation (TENS) differentially modulates sensorimotor cortices: an MEG study.

Objective: Transcutaneous electrical nerve stimulation (TENS) affects excitability of the central motor system as well as the somatosensory system. To determine whether TENS has influence on excitability in the sensorimotor cortices of TENS-treated finger muscle, we investigated magnetoencephalogram associated with voluntary, self-paced finger movement before and after TENS.

Methods: High-frequency TENS was applied on the extensor digitorum muscle for 15 min. Subjects underwent alternate middle finger and thumb extension movements before and after the TENS. We recorded movement-related cortical magnetic field (MRCF) associated with TENS-treated middle finger movement and that from untreated thumb movement.

Results: The current source for motor field (MF) was located in the pre-central motor cortex and anteriorly-oriented, and that for motor evoked field one (MEF1) was found in the post-central somatosensory cortex and posteriorly-oriented. The amplitude of MF for TENS-treated middle finger movement decreased but unchanged for untreated thumb movement after TENS. The amplitude of MEF1 decreased for either finger movement after TENS.

Conclusion: High-frequency TENS to the forearm muscle modulates excitability of the limited area of motor cortex but wider area of primary somatosensory cortex.

Significance: High-frequency TENS to the forearm muscle modulates excitability of the primary somatosensory cortex and motor cortex in a different manner.