  Transcranial alternating current stimulation (tACS) is becoming an important
method in the field of motor rehabilitation because of its ability to
non-invasively influence ongoing brain oscillations at arbitrary frequencies.
However, substantial variations in its effect across individuals are reported,
making tACS a currently unreliable treatment tool. One reason for this
variability is the lack of knowledge about the exact way tACS entrains and
interacts with ongoing brain oscillations. The present crossover stimulation
study on 20 healthy subjects contributes to the understanding of
cross-frequency effects of gamma (70 Hz) tACS over the contralateral motor
cortex by providing empirical evidence which is consistent with a role of low-
(12~-20 Hz) and high- (20-~30 Hz) beta power as a mediator of gamma-tACS on
motor performance.
