Effects on motor learning of transcranial alternating current stimulation applied over the primary motor cortex and cerebellar hemisphere

Transcranial alternating current stimulation (tACS) is a non-invasive method of brain stimulation that modulates oscillatory neural activity in the cortical area under the electrodes. Gamma (gamma)-tACS applied over the primary motor cortex (M1) and cerebellar hemisphere is known to improve motor performance; however, it is not yet known whether it affects motor learning. Thus, here we investigated whether gamma-tACS applied over the Ml and cerebellar hemisphere affects motor learning. This study involved 30 healthy subjects (14 females, 16 males) performing a visuomotor control task (eight trials) during an administration of either gamma-tACS or a sham stimulation (15 subjects per condition) over their right Ml and left cerebellar hemisphere. Each subject performed five trials after 24 h. The motor learning efficiency, motor learning retention and re-motor learning efficiency in each condition were compared. The motor learning retention in the gamma-tACS condition was significantly higher than that in the sham condition (p = 0.031). Thus, subjects who were administered gamma-tACS maintained their motor performance the next day better than sham-stimulated subjects. There was no significant difference between the conditions in the motor learning efficiency and those in the re-motor learning efficiency. Our results demonstrate that gamma-tACS administered over the Ml and cerebellar hemisphere during a motor learning task can enhance motor learning retention. (C) 2020 Elsevier Ltd. All rights reserved.