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.

The purpose of this study was to assess the influence of ageing on reaching motion using a simple and quantitative method. An Electronic Evaluation System of Upper Extremity Function incorporating a motion sensor was used to monitor kinematic changes during a whack-a-mole type task. Sixteen healthy elderly adults (3 males and 13 females, mean age 78.8±6.0 years) and nineteen young adults (3 males and 16 females, mean age 22.1±2.8 years) participated in this study. The participants were asked to continue tapping 16 targets randomly presented on the screen. Based on the kinematic data, the tremor value, spatial travel distance, tapping time, and maximal spatial acceleration were calculated. Differences between elderly and young adults were tested using unpaired-t test. Significant differences were observed in all kinematic parameters, suggesting decreased reaching motion in elderly adults. Moreover, overall positive correlations between parameters were found. Our results suggest that kinematic parameters calculated from the motion sensor technology could be useful to evaluate reaching motion quantitatively and simply.

Bilateral information in primary motor cortices of human cerebral hemispheres is needed to produce simultaneous bilateral limb movement. The corpus callosum connecting homologous areas of cortex between the hemispheres is an important area to exert bilateral finger movements. It is unclear that the movement state of both fingers influences corticospinal excitability involving in contralateral movement. We measured corticospinal excitability during passive movement of both fingers using transcranial magnetic stimulation (TMS) on the primary motor cortex. The subjects performed passive movement of fingers using servomotors. TMS was applied at the two movement states of maximum flexion and extension position on metacarpophalangeal joint (MP joint) of dominant index finger, respectively. There were three kinds of movement task of symmetry, asymmetry and one-finger movements in this experiment. In one-finger movement task, the highest motor evoked potential (MEP) in electromyogram was measured with TMS timing of maximum extension of MP joint angle. Moreover, MEP with maximum extension of MP joint was lowest in symmetry movement task, but the MEP was conversely lowest with maximum flexion in asymmetry movement task. These results suggested that MEP depended on MP joint angle and the corticospinal excitability was inhibited when contralateral MP joint angle was with maximum extension.

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.

Transcranial Magnetic Stimulation (TMS) is a non-invasive technique for neurological research and therapy, but its effectiveness depends on accurate and stable coil placement. Manual localization based on anatomical landmarks is time-consuming and operator-dependent, while state-of-the-art robotic and neuronavigation systems achieve high accuracy using optical tracking with head-mounted markers and infrared cameras, at the cost of increased system complexity and setup burden. This study presents a cost-effective, markerless robotic-assisted TMS system that combines a 3D depth camera and textile capacitive sensors to assist coil localization and contact control. Facial landmarks detected by the depth camera are used to estimate the motor cortex (C3) location without external tracking markers, while a dual textile-sensor suspension provides compliant “soft-landing” behavior, contact confirmation, and coil-tilt estimation. Experimental evaluation with five participants showed reliable C3 targeting with valid motor evoked potentials (MEPs) obtained in most trials after initial calibration, and tilt-verification experiments revealed that peak MEP amplitudes occurred near balanced sensor readings in 12 of 15 trials (80%). The system employs a collaborative robot designed in accordance with international human–robot interaction safety standards, including force-limited actuation and monitored stopping. These results suggest that the proposed approach can improve the accessibility, safety, and consistency of TMS procedures while avoiding the complexity of conventional optical tracking systems.