The effect of transcranial alternating current stimulation (tACS) at alpha and beta frequency on motor learning

At present it remains elusive to what extent motor-cortical alpha (8-12Hz) and beta (13-30Hz) oscillations are associated with motor sequence learning. In order to interact with motor-cortical oscillations, the present study applied transcranial alternating current stimulation (tACS) at 10Hz, 20Hz and sham stimulation over the left primary motor cortex (M1) during a serial reaction time task (SRTT) in 13 healthy volunteers. In a control experiment, tACS at 35Hz was applied in another sample of 13 volunteers. The participants performed the task with the right hand. A sequential pattern was interleaved by a randomly varying pattern serving as interference from sequence learning. Reaction times were determined as dependent variable. Both 10 and 20Hz tACS facilitated SRTT acquisition in contrast to sham and 35Hz tACS. After acquisition, the interfering condition led to increased reaction times comparable to baseline level during 10Hz, sham and 35Hz tACS. In contrast, during 20Hz tACS the initial learning success was retained despite interference. While motor-cortical tACS at 10 and 20Hz likewise facilitates the acquisition, tACS at 20Hz frequency additionally stabilizes the newly learned motor sequence indicated by less susceptibility to interference.