title: Transcranial Alternating Current Stimulation at Beta Frequency: Lack of Immediate Effects on Excitation and Interhemispheric Inhibition of the Human Motor Cortex.
abstract: Transcranial alternating current stimulation (tACS) is a form of noninvasive brain stimulation and is capable of influencing brain oscillations and cortical networks. In humans, the endogenous oscillation frequency in sensorimotor areas peaks at 20 Hz. This beta-band typically occurs during maintenance of tonic motor output and seems to play a role in interhemispheric coordination of movements. Previous studies showed that tACS applied in specific frequency bands over primary motor cortex (M1) or the visual cortex modulates cortical excitability within the stimulated hemisphere. However, the particular impact remains controversial because effects of tACS were shown to be frequency, duration and location specific. Furthermore, the potential of tACS to modulate cortical interhemispheric processing, like interhemispheric inhibition (IHI), remains elusive. Transcranial magnetic stimulation (TMS) is a noninvasive and well-tolerated method of directly activating neurons in superficial areas of the human brain and thereby a useful tool for evaluating the functional state of motor pathways. The aim of the present study was to elucidate the immediate effect of 10 min tACS in the β-frequency band (20 Hz) over left M1 on IHI between M1s in 19 young, healthy, right-handed participants. A series of TMS measurements (motor evoked potential (MEP) size, resting motor threshold (RMT), IHI from left to right M1 and vice versa) was performed before and immediately after tACS or sham using a double-blinded, cross-over design. We did not find any significant tACS-induced modulations of intracortical excitation (as assessed by MEP size and RMT) and/or IHI. These results indicate that 10 min of 20 Hz tACS over left M1 seems incapable of modulating immediate brain activity or inhibition. Further studies are needed to elucidate potential aftereffects of 20 Hz tACS as well as frequency-specific effects of tACS on intracortical excitation and IHI.
authors.affiliation: Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences Leipzig, Germany.
authors.forename: Viola
authors.initials: V
authors.lastname: Rjosk
authors.affiliation: Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences Leipzig, Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Kaminski
authors.affiliation: Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences Leipzig, Germany.
authors.forename: Maike
authors.initials: M
authors.lastname: Hoff
authors.affiliation: Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany; Institute of Psychology, University of LeipzigLeipzig, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Gundlach
authors.affiliation: Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany; Mind and Brain Institute, Charité and Humboldt UniversityBerlin, Germany.
authors.forename: Arno
authors.initials: A
authors.lastname: Villringer
authors.affiliation: Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences Leipzig, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Sehm
authors.affiliation: Department of Neurology, Max Planck Institute for Human Cognitive and Brain SciencesLeipzig, Germany; Institute for General Kinesiology and Exercise Science, University of LeipzigLeipzig, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Ragert
keywords: interhemispheric inhibition (IHI); motor cortical excitability; neuroplasticity; transcranial alternating current stimulation (tACS); transcranial magnetic stimulation (TMS)