Transcranial Alternating Current Stimulation (tACS) to Improve Motor Skill Acquisition in Stroke Patients

Hand motor function is often severely affected in stroke patients and recovery of function is a primary goal in stroke rehabilitative treatment programs. Recently, theta-gamma tACS has been shown to enhance motor skill acquisition in healthy individuals [Akkad et al.2021]. The aim of the present study is to examine the effect of theta-gamma tACS on motor skill acquisition in chronic stroke patients.

In a randomized, controlled, triple-blind trial, chronic stroke patients with an initially impaired hand motor function will receive either (i) theta-gamma peak stimulation (TGP) or (ii) sham stimulation. TGP stimulation significantly improved motor learning in the study by Akkad et al (2021) compared to sham stimulation. tACS will be delivered through a five-electrode montage centered over the sensorimotor cortex on the lesioned side of the brain for approximately 38 min. During stimulation patients will perform a motor skill acquisition task performed with the affected hand. The task consists of short repetitive trials in which participants alternately press two buttons with their thumb. It is designed in a way that participants can improve their performance, more precisely the speed of button presses, and are encouraged to do so. To reduce skin sensations beneath the stimulation electrodes and thereby improve blinding compared to sham stimulation, a local anesthetic consisting of lidocaine and prilocaine will be administered underneath the stimulation electrodes.

Based on the results of the study by Akkad et al. (2021) and on the assumption that theta-gamma phase amplitude coupling is a key mechanism for motor skill acquisition, the investigators hypothesize that motor skill acquisition will differ significantly between the TGP and sham group.

Inclusion criteria

• German-speaking
• ability to perform a thumb movement task with the affected hand
• first-ever clinical ischemic stroke in the chronic phase
• persistent mild motor deficit of the upper extremity or motor deficit of the upper extremity in the acute phase over >24h

Exclusion criteria

• pronounced cognitive deficits
• history of major neurological or psychiatric illness other than stroke
• epilepsy or epileptic seizure in the history
• any devices or implants in the head region (e.g. cochlear implant, aneurysm clips),
• implanted pacemaker or medical pumps
• intake of psychotropic medication
• allergy to any ingredient of the local anesthetic cream
• pregnancy