High voltage electrical stimulation of the proximal hypoglossal nerve in normal subjects

Objectives: It is often difficult to stimulate the proximal hypoglossal nerve by magnetic occipital stimulation, even in normal subjects. Therefore, we tested an improved method of stimulating the proximal hypoglossal nerve, using high voltage electrical stimulation. Methods: The proximal hypoglossal nerve was activated by high voltage electrical stimulation using surface electrodes over the occipital skull. The compound muscle action potential (CMAP) was recorded from the lingual muscles using surface electrodes in 10 normal subjects. CMAP and F waves produced by distal hypoglossal nerve stimulation and motor evoked potentials produced by transcranial magnetic stimulation were also recorded. Results: When the anode electrode was placed at the mastoid process and the cathode below the inion, the unilateral proximal hypoglossal nerve was readily stimulated supramaximally in all the subjects. The CMAP latency was the same as that obtained with magnetic occipital stimulation. The central motor conduction time (CMCT) calculated from the proximal CMAP was 4.1±0.4 ms in the contralateral corticobulbar tract and 4.4±0.4 ms in the ipsilateral. The CMCT calculated from the minimal F wave latency was 3.3±0.2 ms. Conclusions: The high voltage electrical stimulation is a useful method for stimulating the proximal hypoglossal nerve to estimate the CMCT of the corticobulbar tract.