title: Inhibition of motor cortex excitability with 15Hz transcranial alternating current stimulation (tACS).
abstract: There remains a lack of solid evidence showing whether transcranial stimulation with weak alternating current (transcranial alternating current stimulation, tACS) can in fact induce significant neurophysiological effects. Previously, a study in which tACS was applied for 2 and 5min with current density=0.16-0.25A/m(2) was unable to show robust effects on cortical excitability. Here we applied tACS at a significantly higher current density (0.80A/m(2)) for a considerably longer duration (20min) and were indeed able to demonstrate measurable changes to cortical excitability. Our results show that active 15Hz tACS of the motor cortex (electrodes placed at C3 and C4) significantly diminished the amplitude of motor evoked potentials and decreased intracortical facilitation (ICF) as compared to baseline and sham stimulation. In addition, we show that our method of sham tACS is a reliable control condition. These results support the notion that AC stimulation with weak currents can induce significant changes in brain excitability; in this case, 15Hz tACS led to a pattern of inhibition of cortical excitability. We propose that tACS may have a dampening effect on cortical networks and perhaps interfere with the temporal and spatial summation of weak subthreshold electric potentials.
authors.affiliation: Laboratory of Neuromodulation, Spaulding Rehabilitation Hospital, Harvard Medical School, 125 Nashua Street #727, Boston, MA 02114, USA.
authors.forename: Soroush
authors.initials: S
authors.lastname: Zaghi
authors.forename: Larissa
authors.initials: L
authors.lastname: de Freitas Rezende
authors.forename: Laís Machado
authors.initials: LM
authors.lastname: de Oliveira
authors.forename: Rasheda
authors.initials: R
authors.lastname: El-Nazer
authors.forename: Sanne
authors.initials: S
authors.lastname: Menning
authors.forename: Laura
authors.initials: L
authors.lastname: Tadini
authors.forename: Felipe
authors.initials: F
authors.lastname: Fregni
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*