AUTHOR=Tian Dongting , Izumi Shin-Ichi 

TITLE=Different effects of I-wave periodicity repetitive TMS on motor cortex interhemispheric interaction

JOURNAL=Frontiers in Neuroscience

VOLUME=Volume 17 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1079432

DOI=10.3389/fnins.2023.1079432

ISSN=1662-453X

ABSTRACT=Activity of the neural circuits in the human motor cortex underlying transcranial magnetic stimulation (TMS) can be plastically modulated by I-wave periodicity repetitive TMS (iTMS). Reversing TMS-induced current direction also results in different I-wave recruitment. Here, we explored the modulation of interhemispheric interaction by iTMS applied in different current directions. Twenty right-handed healthy young volunteers (aged 27.5 ± 5.0 years) participated in this study with three visits. On each visit, iTMS in posterior-anterior/anterior-posterior direction (PA-/AP-iTMS) or sham-iTMS was applied to the right hemisphere, with corticospinal excitability and intracortical facilitation of the non-stimulated left hemisphere evaluated at four timepoints. Ipsilateral silent period was also measured at each timepoint probing interhemispheric inhibition (IHI). PA-and AP-iTMS potentiated cortical excitability concurrently in the stimulated right hemisphere. Corticospinal excitability of the non-stimulated left hemisphere increased 10 minutes after both PAand AP-iTMS intervention, with a decrease in short-interval intracortical facilitation (SICF) observed in AP-iTMS only. Immediately after the intervention, PA-iTMS tilted the IHI balance towards inhibiting the non-stimulated hemisphere, while AP-iTMS shifted the balance towards the opposite direction. Our findings provide systematic evidence on the plastic modulation of interhemispheric interaction by PA-and AP-iTMS. We concluded that iTMS induces an interhemispheric facilitatory effect, and that PA-and AP-iTMS differs in modulating interhemispheric inhibition.