Gamma Transcranial Alternating Current Stimulation Has Frequency-Dependent Effects on Human Motor Cortex Plasticity...

Area of Science:

• Neuroscience
• Motor Control
• Brain Stimulation

Background:

• Intermittent theta burst stimulation (iTBS) induces long-term potentiation (LTP)-like plasticity in the primary motor cortex (M1).
• Transcranial alternating current stimulation (tACS) at gamma frequencies can modulate this plasticity, with previous studies suggesting a 70 Hz frequency is optimal.
• Evidence indicates frequency specificity within the mid-gamma band (60-90 Hz) for tACS effects on motor function.

Purpose of the Study:

• To investigate the impact of different gamma band tACS frequencies (60, 75, and 90 Hz) on neuroplasticity induced by iTBS.
• To determine if specific gamma frequencies enhance the motor cortex's response to iTBS.

Main Methods:

• Seventeen healthy young adults participated in four experimental sessions.
• A tACS-iTBS costimulation approach was used, applying iTBS over M1 combined with sham or 60, 75, or 90 Hz tACS.
• Transcranial magnetic stimulation (TMS) assessed motor evoked potential (MEP) amplitude and short-interval intracortical inhibition (SICI) with posterior-anterior (PA) and anterior-posterior (AP) coil orientations before and after interventions.

Main Results:

• Costimulation with 90 Hz gamma tACS significantly increased PA and AP MEP amplitudes compared to sham tACS, while 60 Hz and 75 Hz did not.
• Both PA and AP SICI were reduced by tACS-iTBS costimulation, irrespective of the gamma tACS frequency.
• The largest enhancement of LTP-like plasticity was observed at the highest gamma frequency tested (90 Hz).

Conclusions:

• Gamma tACS, particularly at higher frequencies (90 Hz), can enhance iTBS-induced LTP-like plasticity in the primary motor cortex.
• The frequency of gamma tACS plays a crucial role in modulating motor cortex plasticity.
• Further research is needed to explore the functional relevance of targeting higher gamma frequencies in diverse brain areas and populations.