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Ipsilateral and contralateral cortical control of the external oblique muscles revealed by TMS
Journal article   Peer reviewed

Ipsilateral and contralateral cortical control of the external oblique muscles revealed by TMS

Ryoji Miyano, Yuichiro Shirota, Satoshi Kodama, Tatsushi Toda and Masashi Hamada
Clinical neurophysiology, Vol.181, pp.2111400-2111400
01/01/2026
DOI: 10.1016/j.clinph.2025.2111400
PMID: 41197531
url
https://doi.org/10.1016/j.clinph.2025.2111400View
Published (Version of record) Open Access

Abstract

•Onset latencies and active motor threshold by ipsilateral stimulation vary depending on the current direction.•Optimal coil orientation for ipsilateral stimulation is the same as that for contralateral stimulation.•They give a foundation for further exploration of the relation between contralateral and ipsilateral motor evoked potentials. Transcranial magnetic stimulation (TMS) is used widely to explore human motor function. This study was conducted to investigate the differences between contralateral and ipsilateral cortical control on trunk muscles for eliciting contralateral and ipsilateral motor evoked potentials (MEPs) in the external oblique muscles. Twenty healthy participants were examined: 10 younger and 10 older adults. They underwent TMS to locate contralateral and ipsilateral hot spots. For the identified hot spots in the younger group, the coil was positioned in eight orientations, each separated by 45 degrees, to measure active motor threshold (AMT) and onset latencies. Contralateral MEPs were obtained from all participants, whereas ipsilateral MEPs were detected in 14 out of 20 participants. The ipsilateral hot spots were located more laterally from Cz (p < 0.05). Coil orientation that induced an antero-medially directed current in the brain produced the shortest onset latency and lowest AMT for both stimulations. However contralateral MEPs required lower AMT and exhibited shorter onset latency than ipsilateral MEPs (p < 0.05). Ipsilateral motor pathways of the external oblique muscles have physiological features unlike those of contralateral motor pathways. These findings suggest differential cortical control between contralateral and ipsilateral pathways in trunk muscles and provide bases for additional investigations into ipsilateral motor control.
 Coil orientation External oblique muscle Hot spot Ipsilateral motor evoked potential Motor threshold Onset latency Transcranial magnetic stimulation

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