The study intervention is to perform standard somatosensory evoked responses limited to the face during rhizotomy procedures of the gasserian ganglion (trigeminal ganglion) for the treatment of trigeminal neuralgia. The evoked responses will be measured at two locations before and after the clinical rhizotomy including: the standard contralateral scalp (EEG) and at the gasserian ganglion through an FDA-approved recording electrode.