The study aimed to determine whether tACS at various frequencies (beta: 20 Hz, low gamma: 40 Hz, mid gamma: 60 Hz, high gamma: 80 Hz) over the bilateral motor cortex modulates corticomotor plasticity and motor performance. A secondary objective was to explore how these frequencies impact hand dexterity and reaction time through the Grooved Pegboard Test (GPT) and sensorimotor tasks.
This single-blind, sham-controlled, cross-over study involved 12 healthy young adults. Participants received tACS at 20 Hz, 40 Hz, 60 Hz, and 80 Hz, with corticospinal and intracortical responses assessed via surface electromyography (sEMG) and transcranial magnetic stimulation (TMS) at multiple time points (pre, post 0, post 30, post 60). Motor performance was measured using the GPT and reaction time tests. Statistical analysis used Linear Mixed Models to assess frequency-specific effects on cortical excitability and motor outcomes.
Distinct frequency effects were observed on corticomotor excitability, silent period (SP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Specifically, 20 Hz and 40 Hz tACS reduced Motor Evoked Potential (MEP) amplitude, indicating inhibitory effects, while 60 Hz and 80 Hz tACS significantly increased MEP amplitude, showing excitatory effects. Silent period reductions were more consistent with 20 Hz and 40 Hz tACS. Motor performance improvements correlated with 60 Hz and 80 Hz tACS effects on corticospinal excitability.
Different tACS frequencies modulate corticomotor excitability and motor performance. Beta and low gamma frequencies exert inhibitory effects, while mid and high gamma frequencies enhance excitability. Gamma frequencies, particularly 60 Hz and 80 Hz, showed potential in improving motor function. These findings suggest frequency-specific applications of tACS in motor rehabilitation, with future research needed to explore long-term effects and clinical applications.
The study’s findings have significant implications for physiotherapy. Understanding the frequency-specific effects of tACS on motor outcomes can inform neuromodulation-based treatments for motor impairments. Physiotherapists could integrate tACS into rehabilitation to enhance motor function, while incorporating neuromodulation into education and clinical practice. From a policy perspective, these results support the inclusion of tACS in motor rehabilitation guidelines and call for increased investment in research and training to optimise patient outcomes.
Corticospinal Excitability
Motor Performance
