Achieving greater accuracy in transcranial magnetic stimulation corticospinal evaluation and motor mapping by improving motor evoked potential recording: an emerging issue.

Accurate evaluation of corticospinal excitability and motor mapping via transcranial magnetic stimulation (TMS) relies heavily on motor evoked potential (MEP) recordings. However, a consensus on optimal surface electrode configurations is lacking. This pilot study investigated the impact of electrode montages on the accuracy of MEP recordings. MEPs were recorded in a healthy male subject (43 years old) using a 64-channel electrode array placed over the right brachioradialis (BR) and biceps brachii (BB) muscles. Two montages—bipolar and pseudomopolar—were simulated to assess differences in MEP peak-to-peak values (MEPP−P). For the BR muscle, MEPP−P were ~ 175 µV (bipolar) and 200 µV (pseudomonopolar), presenting a modest difference. In contrast, the BB muscle presented ~ 40 µV (bipolar) and 200 µV (pseudomonopolar), resulting in a five-fold difference between the two surface electrode montages. The present findings suggest a pivotal role for surface electrode montage in optimizing MEP signal acquisition. Given that the MEP is the key parameter in determining the motor threshold, which in turn serves as a reference for both diagnostic purposes and defining repetitive TMS dosing, there is an imperative need to standardize surface electromyography-based recording protocols.