Determining the effects of transcranial alternating current stimulation on corticomotor excitability and motor performance: A sham-controlled comparison of four frequencies

Mohamad Rostami; Annemarie Lee; Ashlyn K Frazer; Yonas Akalu; Ummatul Siddique; Alan J Pearce; Jamie Tallent; Dawson J Kidgell

doi:10.1016/j.neuroscience.2025.01.016

Determining the effects of transcranial alternating current stimulation on corticomotor excitability and motor performance: A sham-controlled comparison of four frequencies

Neuroscience. 2025 Jan 10:568:12-26. doi: 10.1016/j.neuroscience.2025.01.016. Online ahead of print.

Authors

Mohamad Rostami¹, Annemarie Lee¹, Ashlyn K Frazer¹, Yonas Akalu², Ummatul Siddique¹, Alan J Pearce³, Jamie Tallent⁴, Dawson J Kidgell⁵

Affiliations

¹ Monash Exercise Neuroplasticity Research Unit, Department of Physiotherapy, School of Primary and Allied Health Care, Faculty of Medicine, Nursing and Health Science, Monash University, Melbourne Australia.
² Monash Exercise Neuroplasticity Research Unit, Department of Physiotherapy, School of Primary and Allied Health Care, Faculty of Medicine, Nursing and Health Science, Monash University, Melbourne Australia; Department of Human Physiology School of Medicine University of Gondar Ethiopia.
³ School of Health Science Swinburne University of Technology Melbourne Australia.
⁴ Monash Exercise Neuroplasticity Research Unit, Department of Physiotherapy, School of Primary and Allied Health Care, Faculty of Medicine, Nursing and Health Science, Monash University, Melbourne Australia; School of Sport Rehabilitation and Exercise Sciences University of Essex Colchester UK.
⁵ Monash Exercise Neuroplasticity Research Unit, Department of Physiotherapy, School of Primary and Allied Health Care, Faculty of Medicine, Nursing and Health Science, Monash University, Melbourne Australia. Electronic address: dawson.kidgell@monash.edu.

PMID: 39798837
DOI: 10.1016/j.neuroscience.2025.01.016

Abstract

Transcranial alternating current stimulation (tACS) modulates brain oscillations and corticomotor plasticity. We examined the effects of four tACS frequencies (20 Hz, 40 Hz, 60 Hz, and 80 Hz) on motor cortex (M1) excitability and motor performance. In a randomised crossover design, 12 adults received 20-minute tACS sessions, with Sham as control. Corticomotor and intracortical excitability was measured up to 60-minutes post-tACS. Motor performance was evaluated using the Grooved Pegboard Test (GPT) and sensorimotor assessments. Our findings demonstrated frequency-dependent modulation of corticomotor excitability based on MEP amplitude. 20 Hz and 40 Hz tACS reduced MEPs, while 60 Hz and 80 Hz increased MEPs. Inhibition (cortical silent period, SP) was reduced across all tACS frequencies compared to Sham, with 20 Hz and 40 Hz showing consistent reductions, 60 Hz showing effects at post-0 and post-30, and 80 Hz at post-60. Furthermore, 60 Hz tACS decreased intracortical inhibition at post-0, while intracortical facilitation increased with 20 Hz and 60 Hz at post-0, and 40 Hz at post-60. Motor performance remained unaffected across frequencies. Regression analyses revealed that shorter SP at 60 min post 60 Hz tACS predicted faster reaction times, while greater MEP amplitudes at 60 min following 80 Hz tACS predicted improved hand dexterity. Overall, beta and gamma tACS frequencies modulate M1 excitability, with consistent effects on SP, suggesting potential use in conditions involving SP elongation, such as stroke and Huntington's disease. These findings highlight 60 Hz tACS as a potential tool for motor rehabilitation therapies.

Keywords: Corticomotor excitability; Motor cortex; Motor performance; Non-invasive brain stimulation; Transcranial magnetic stimulation.