Mapping of multiple muscles with transcranial magnetic stimulation: absolute and relative test–retest reliability

• Main Authors: Dobrynina, L. (Author), Ivanina, E. (Author), Kozlova, K. (Author), Nazarova, M. (Author), Nikulin, V.V (Author), Novikov, P. (Author)
• Format: Article
• Language: English
• Published: John Wiley and Sons Inc 2021
• Subjects: abducens nerve; adult; Adult; article; brain mapping; Brain Mapping; clinical article; controlled study; cortical mapping; electromyography; Electromyography; Evoked Potentials, Motor; gravity; hand muscle; human; Humans; Magnetic Resonance Imaging; male; Male; motor cortex; Motor Cortex; motor evoked potential; muscle cortical representation; Muscle, Skeletal; nuclear magnetic resonance imaging; overlap; physiology; procedures; reliability; reproducibility; Reproducibility of Results; skeletal muscle; test retest reliability; transcranial magnetic stimulation; Transcranial Magnetic Stimulation; young adult; Young Adult
• Online Access: View Fulltext in Publisher

 The spatial accuracy of transcranial magnetic stimulation (TMS) may be as small as a few millimeters. Despite such great potential, navigated TMS (nTMS) mapping is still underused for the assessment of motor plasticity, particularly in clinical settings. Here, we investigate the within-limb somatotopy gradient as well as absolute and relative reliability of three hand muscle cortical representations (MCRs) using a comprehensive grid-based sulcus-informed nTMS motor mapping. We enrolled 22 young healthy male volunteers. Two nTMS mapping sessions were separated by 5–10 days. Motor evoked potentials were obtained from abductor pollicis brevis (APB), abductor digiti minimi, and extensor digitorum communis. In addition to individual MRI-based analysis, we studied normalized MNI MCRs. For the reliability assessment, we calculated intraclass correlation and the smallest detectable change. Our results revealed a somatotopy gradient reflected by APB MCR having the most lateral location. Reliability analysis showed that the commonly used metrics of MCRs, such as areas, volumes, centers of gravity (COGs), and hotspots had a high relative and low absolute reliability for all three muscles. For within-limb TMS somatotopy, the most common metrics such as the shifts between MCR COGs and hotspots had poor relative reliability. However, overlaps between different muscle MCRs were highly reliable. We, thus, provide novel evidence that inter-muscle MCR interaction can be reliably traced using MCR overlaps while shifts between the COGs and hotspots of different MCRs are not suitable for this purpose. Our results have implications for the interpretation of nTMS motor mapping results in healthy subjects and patients with neurological conditions. © 2021 The Authors. Human Brain Mapping published by Wiley Periodicals LLC.