Transcranial alternating current stimulation in the low kHz range increases motor cortex excitability

Restor Neurol Neurosci. 2011;29(3):167-75. doi: 10.3233/RNN-2011-0589.


Purpose: External transcranial electric and magnetic stimulation techniques allow for the fast induction of sustained and measurable changes in cortical excitability. Here we aim to develop a paradigm using transcranial alternating current (tACS) in a frequency range higher than 1 kHz, which potentially interferes with membrane excitation, to shape neuroplastic processes in the human primary motor cortex (M1).

Methods: Transcranial alternating current stimulation was applied at 1, 2 and 5 kHz over the left primary motor cortex with a reference electrode over the contralateral orbit in 11 healthy volunteers for a duration of 10 min at an intensity of 1 mA. Monophasic single- pulse transcranial magnetic stimulation (TMS) was used to measure changes in corticospinal excitability, both during and after tACS in the low kHz range, in the right hand muscle. As a control inactive sham stimulation was performed.

Results: All frequencies of tACS increased the amplitudes of motor- evoked potentials (MEPs) up to 30-60 min post stimulation, compared to the baseline. Two and 5 kHz stimulations were more efficacious in inducing sustained changes in cortical excitability than 1 kHz stimulation, compared to sham stimulation.

Conclusions: Since tACS in the low kHz range appears too fast to interfere with network oscillations, this technique opens a new possibility to directly interfere with cortical excitability, probably via neuronal membrane activation. It may also potentially replace more conventional repetitive transcranial magnetic stimulation (rTMS) techniques for some applications in a clinical setting.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Analysis of Variance
  • Biophysics / methods
  • Electric Stimulation / methods
  • Electromyography / methods
  • Evoked Potentials, Motor / physiology
  • Evoked Potentials, Motor / radiation effects*
  • Female
  • Humans
  • Male
  • Motor Cortex / radiation effects*
  • Reaction Time / physiology
  • Reaction Time / radiation effects
  • Time Factors
  • Transcranial Magnetic Stimulation / methods*
  • Young Adult