We reviewed trigeminal nerve stimulation (TNS) and transcutaneous vagus nerve stimulation (tVNS). All techniques have shown preliminary promising results, although the results are mixed.
Method: We performed a systematic review of the Medline and Embase databases, with no constraint to dates, through June 2013. The keywords were [(1) trigeminal nerve stimulation OR (2) cranial nerve OR (3) trigemin* OR (4) transcutaneous VNS OR (5) transcutaneous cranial nerve stimulation] and (6) mental disorders.
Results: We included four preclinical and clinical five studies on TNS. All clinical data were based on open-label studies with small samples, which diminished the external validity of the results, thus reflecting the modest impact of TNS in current clinical practice. Of the tVNS clinical trials, three assessed physiological features in healthy volunteers, and one examined patients with epilepsy.
Conclusion: TNS and tVNS improve treatment of particular neuropsychiatric disorders such as depression.