Direction-Specific Effects of Biphasic Transcranial Magnetic Stimulation on Cortical and Cortico-spinal Excitability

Authors

Osnabruegge, M., Kanig, C., Mack, W., Langguth, B., Schoisswohl, S.

Abstract

Aims & Methods: Transcranial magnetic stimulation (TMS) is a well-established tool for inducing cortical excitation. However, the relevance of current direction on elicited effects is still incompletely understood. Combining TMS with electroencephalography (EEG) and electromyography (EMG) enables non-invasive analysis of evoked potentials both on cortical and peripheral level. In 23 healthy subjects, EEG and EMG responses to biphasic single pulses applied over the left motor cortex with anterior-posterior to posterior-anterior (AP-PA) or PA-AP current direction and 110% resting motor threshold (RMT) intensity were recorded and contrasted between the alternating phases. A cobot-assissted neuronavigation ensured stable coil-placement during the procedure. Results: RMT was lower and EMG latency was shorter for AP-PA currents compared to PA-AP currents, whereas the EMG amplitude did not differ. For EEG responses, local and global evoked activity was higher for mid-components with PA-AP currents. P60 occurred earlier with PA-AP currents and N100 amplitude was higher in amplitude with AP-PA currents. The trial-wise MEP amplitude correlated significantly with P30 in the AP-PA and for both current directions with the N100 amplitude. Conclusion: Our results highlight the directional sensitivity of M1 and the importance of further exploring the role of current direction in TMS protocols to better understand the cortical processes underlying cortico-cortical and cortico-spinal responses.

Preprint server: bioRxiv
The authors list and abstract were imported from bioRxiv on 31 Jul 2026.

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