AI Insight
This study investigated how the direction of magnetic current in transcranial magnetic stimulation (TMS) affects brain and muscle responses in 23 healthy subjects. Researchers found that anterior-posterior to posterior-anterior (AP-PA) current direction required lower intensity to activate muscles and produced shorter response times, while posterior-anterior to anterior-posterior (PA-AP) direction generated stronger mid-range brain activity measured by EEG. The study demonstrates that current direction significantly influences both cortical brain responses and cortico-spinal pathways connecting the brain to muscles.
Why it matters
These findings could help optimize TMS protocols for both research and clinical applications, such as treating depression or stroke rehabilitation, by identifying which current direction produces desired effects. Understanding directional sensitivity may improve the precision and effectiveness of TMS treatments by allowing practitioners to target specific neural pathways more accurately.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
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.