Objectives: The use of noninvasive cortical electrical stimulation with weak currents has significantly increased in basic and clinical human studies. Initial, preliminary studies with this technique have shown encouraging results; however, the safety and tolerability of this method of brain stimulation have not been sufficiently explored yet. The purpose of our study was to assess the effects of direct current (DC) and alternating current (AC) stimulation at different intensities in order to measure their effects on cognition, mood, and electroencephalogram.
Methods: Eighty-two healthy, right-handed subjects received active and sham stimulation in a randomized order. We conducted 164 ninety-minute sessions of electrical stimulation in 4 different protocols to assess safety of (1) anodal DC of the dorsolateral prefrontal cortex (DLPFC); (2) cathodal DC of the DLPFC; (3) intermittent anodal DC of the DLPFC and; (4) AC on the zygomatic process. We used weak currents of 1 to 2 mA (for DC experiments) or 0.1 to 0.2 mA (for AC experiment).
Results: We found no significant changes in electroencephalogram, cognition, mood, and pain between groups and a low prevalence of mild adverse effects (0.11% and 0.08% in the active and sham stimulation groups, respectively), mainly, sleepiness and mild headache that were equally distributed between groups.
Conclusions: Here, we show no neurophysiological or behavioral signs that transcranial DC stimulation or AC stimulation with weak currents induce deleterious changes when comparing active and sham groups. This study provides therefore additional information for researchers and ethics committees, adding important results to the safety pool of studies assessing the effects of cortical stimulation using weak electrical currents. Further studies in patients with neuropsychiatric disorders are warranted.
From the *Laboratory of Neuromodulation, Spaulding Rehabilitation Hospital, Harvard Medical School, Boston, MA; †Centro Clinico per le Neuronanotecnologie e la Neurostimolazione, ‡Unità Operativa di Neurofisiologia Clinica, Fondazione IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena; §Dipartimento di Scienze Neurologiche, Università di Milano, Milan, Italy; ∥Department of Neurology, Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA; ¶Department of Neurosciences and Behavior, Institute of Psychology, University of São Paulo; and **Laboratório de Neurociência Cognitiva e Programa de Transtorno do Desenvolvimento, Centro de Saúde e Ciências Biológicas, Universidade Presbiteriana Mackenzie, Sao Paulo, Brazil.
Received for publication January 20, 2010; accepted April 14, 2010.
Reprints: Felipe Fregni, MD, PhD, Laboratory of Neuromodulation, Spaulding Rehabilitation Hospital, Harvard Medical School, 125 Nashua St, Boston, MA 02114 (e-mail: firstname.lastname@example.org).
Equally contributing authors were Laura Tadini, Rasheda El-Nazer, and Andre Brunoni.
Disclosures: The authors have no conflicts of interest.
Funding: This work was funded through a study grant provided by Aspect Medical Systems to F.F. L.T. is funded by a grant from Fondazione IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Milan, Italy and the Dipartimento di Scienze Neurologiche, Università di Milano, Milan, Italy.