Influence of Concurrent Theta-Gamma Transcranial Alternating Current Stimulation and Repetitive Transcranial Magnetic...

Area of Science:

• Neuroscience
• Motor Control
• Brain Stimulation

Background:

• Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique.
• Combined theta-gamma (TG) tACS waveforms show potential for enhancing motor performance.
• The impact of TG tACS on primary motor cortex (M1) plasticity is not well understood.

Purpose of the Study:

• To investigate the effects of concurrent TG tACS and repetitive paired-pulse transcranial magnetic stimulation (rppTMS) on M1 excitability and plasticity.
• To compare the effects of different tACS conditions (peak-coupled, trough-coupled, theta-only) against sham stimulation.

Main Methods:

• 22 healthy adults underwent four experimental sessions with concurrent tACS and rppTMS over M1.
• rppTMS (1.5 ms ISI) was applied during TGP, TGT, TP, or sham tACS.
• Motor-evoked potential (MEP) amplitude, short-interval intracortical inhibition (2 ms ISI), and facilitation (1.5 ms ISI) were measured pre- and post-intervention.

Main Results:

• Active tACS (TGP, TGT, TP) increased MEP amplitude during rppTMS (online effect), unlike sham.
• Post-intervention, single-pulse MEP amplitude and short-interval intracortical facilitation increased, while inhibition decreased.
• These offline neuroplastic changes did not differ significantly across tACS conditions.

Conclusions:

• tACS increased M1 excitability during concurrent rppTMS but did not differentially affect excitability based on TG coupling or theta-only stimulation.
• TG tACS did not modulate the offline neuroplastic effects induced by rppTMS.
• Future research should explore tACS efficacy during motor tasks, which may engage broader motor networks.