Background Transcranial magnetic stimulation (TMS), when applied over the primary motor cortex, elicits a motor-evoked potential (MEP) in electromyograms measured from peripheral muscles. MEP amplitude has often been observed to fluctuate trial to trial, even with a constant stimulus. Many factors cause MEP fluctuations in TMS. One of the primary factors is the weak stationarity and instability of cortical activity in the brain, from which we assumed MEP fluctuations originate. We hypothesized that MEP fluctuations are suppressed when TMS is delivered to the primary motor cortex at a time when several electroencephalogram (EEG) channels measured on the scalp are highly similar in the frequency domain. Objective We developed a TMS triggering system to suppress MEP fluctuations using EEG coherence analysis, which was performed to detect the EEG signal similarity between the 2 channels in the frequency domain. Methods Seven healthy adults participated in the experiment to confirm whether the TMS trigger system works adequately, and the mean amplitude and coefficient of the MEP variation were recorded and compared with the values obtained during the control task. We also determined the experimental time under each condition and verified whether it was within the predicted time. Results The coefficient of variation of MEP amplitude decreased in 5 of the 7 participants, and significant differences (P=.02) were confirmed in 2 of the participants according to an F test. The coefficient of variation of the experimental time required for each stimulus after threshold modification was less than that without threshold modification, and a significant difference (P<.001) was confirmed by performing an F test. Conclusions We found that MEP could be suppressed using the system developed in this study and that the TMS trigger system could also stabilize the experimental time by changing the triggering threshold automatically.
Transcranial magnetic stimulation (TMS) is a non-invasive stimulation method for cortical neurons. When TMS is delivered to the primary motor cortex (M1), motor evoked potentials can be measured in electromyograms for the peripheral muscle. However, the motor-evoked potential (MEP) amplitudes measured by stimulations for M1 fluctuated from trial to trial. MEP fluctuations are caused by changes in cortical excitability. We hypothesized that MEP variability could be suppressed with application of TMS when cortical excitability was stable. Thus, we developed a TMS system to suppress MEP amplitude variabilities. We used electroencephalographic (EEG) online measurements with coherence analysis to obtain the similarity of cortical excitabilities. The system enables us to trigger TMS if the EEGs measured from the two channels have a high similarity in the frequency domain. In this study, we found that the suppression of MEP fluctuation was dependent on the state of cortical excitability obtained by EEG coherence analysis.
BACKGROUND Transcranial magnetic stimulation (TMS), when applied over the primary motor cortex (M1) elicits a motor evoked potential (MEP) in electromyograms measured from peripheral muscles. MEP amplitude has often been observed to fluctuate trial by trial, even with a constant stimulus. Many factors cause MEP fluctuations in TMS. One of the primary factors is the weak stationarity and instability of cortical activity in the brain, from which we assumed MEP fluctuations originated. We hypothesized that MEP fluctuations must be suppressed if TMS is delivered to M1 at the time when several electroencephalogram (EEG) channels measured on the scalp have high similarity in the frequency domain. OBJECTIVE We developed a TMS triggering system for suppressing MEP fluctuations using EEG coherence analysis, which was performed to detect the EEG signal similarity between the two channels in the frequency domain. METHODS Seven healthy adults participated in the experiment to confirm whether the TMS trigger system works adequately, and the mean amplitude and coefficient of variation of the MEP were recorded and compared with the values in the control task. We also determined the experimental time under each condition and verified whether it was within the predicted time. RESULTS The coefficient of variation (CV) of MEP amplitude decreased in five out of seven subjects, and significant differences (P=.02) were confirmed in two of the subjects by performing an F-test. The CV of the experimental time required for each stimulus with threshold modification was less than that without threshold modification, and a significant difference (P<.001) was confirmed by performing an F-test. CONCLUSIONS We consequently found that MEP could be suppressed using the system developed in this study and that the TMS trigger system could also stabilize the experimental time by changing the triggering threshold automatically.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.