A Novel Scalp Acupuncture-based Method to Target the Hand Motor Hotspot for Non-invasive Brain Stimulation

The precise localization of the primary motor cortex (M1) corresponding to specific muscles is critical for enhancing the efficacy of neuromodulation. When navigated transcranial magnetic stimulation (nTMS) or other mapping tools are unavailable, stimulation is typically applied at the C3 site of the standard 10-20 EEG system. However, emerging evidence indicates that C3 may not be the optimal site for targeting hand muscles. Therefore, the goal of this study is to propose an innovative neuroanatomy-based localization method to identify the M1 hotspot for the hand muscle and to validate its effectiveness compared with the C3 site. A step-by-step protocol was developed to identify the M1 hotspot for the flexor digitorum superficialis (FDS) muscle using an acupuncture-based approach. The identified hotspot was then compared with the conventional C3 site by evaluating baseline and post-neuromodulation motor evoked potentials (MEPs). Representative data demonstrated that the proposed M1 hotspot yielded significantly higher MEP amplitudes than the C3 site, both at the baseline and following neuromodulation. The proposed approach provides a validated and practical method for localizing the M1 hotspot for the FDS. This technique has the potential to improve the effectiveness of neuromodulation in clinical practice when advanced neuroimaging tools are not accessible.