Parameter Space of kTMP

Primary outcomes

1. Self-reported sensation/discomfort through questionnaire during kTMP stimulation.

   Time frame: Measures will be obtained 4-5 seconds after each kTMP stimulation at a specific E-field (when the visual display appears on the screen), in total 16 times throughout the kTMP stimulation trial.

   As per the FDA's guidance (www.fda.gov/media/81784/download) on device feasibility studies, initiation of an early feasibility study must be justified by an appropriate benefit-risk analysis and adequate human subject protection measures. This outcome measures device feasibility in terms of device tolerability. To estimate the stimulation threshold, the investigators will use an adaptive procedure in which they sequentially increase the stimulation intensity (E-field amplitude) and register self-reports of sensation. Stimulation intensity will start from 0.01 V/m (sham) increasing 0.5 V/m at a time for 16 trials until it reaches 7.6 V/m. Participants provided three ratings using an 11-point scale (0 = not at all; 10 = extremely) in response to questions on annoyance, pain, and muscle twitching. ("How annoying was kTMP?", "How painful was kTMP?", and "If there were any muscle twitches from the kTMP, how strong were they?") A higher score means more sensation/discomfort.

2. Self-reported sensation/discomfort through questionnaire after kTMP stimulation.

   Time frame: Measures will be obtained 1 minute after kTMP stimulation.

   As per the FDA's guidance (www.fda.gov/media/81784/download) on device feasibility studies, initiation of an early feasibility study must be justified by an appropriate benefit-risk analysis and adequate human subject protection measures. This outcome measures device feasibility in terms of device tolerability. After the kTMP stimulation, the investigators will register self-reports of sensation from the participant to see any lasting effect in terms of sensation. Participants provided three ratings using an 11-point scale (0 = not at all; 10 = extremely) in response to questions on annoyance, pain, and muscle twitching. ("How annoying was kTMP?", "How painful was kTMP?", and "If there were any muscle twitches from the kTMP, how strong were they?") A higher score means more sensation/discomfort.

3. Motor evoked potential (MEPs) amplitude recorded with electromyography (EMG) before kTMP stimulation.

   Time frame: Measures will be obtained from 0 to 15 minutes before the stimulation.

   This outcome measures device feasibility in terms of efficacy, as MEP changes indicate changes in cortical excitability induced by kTMP. As an operational definition of cortical excitability, the investigators will measure MEPs recorded in a peripheral hand muscle through the EMG system. The threshold procedure will be first conducted using single-pulse Transcranial magnetic stimulation (TMS) to find the M1 hotspot and threshold intensity. Once the threshold is set, MEPs will be obtained using the single-pulse and paired-pulse TMS procedures. These measurements will be taken prior to the experimental intervention of kTMP to obtain a baseline measure.

4. Motor evoked potential (MEPs) amplitude recorded with EMG after kTMP stimulation.

   Time frame: Measures will be obtained 1 hour 30 minutes after the stimulation.

   This outcome measures device feasibility in terms of efficacy, as MEP changes indicate changes in cortical excitability induced by kTMP. After the kTMP stimulation as a plasticity-inducing technique, we obtain MEPs using the single-pulse and paired-pulse TMS procedures. MEPs will be recorded in a peripheral hand muscle through the EMG system. The primary intervention of interest is the kTMP system, with various manipulations of the parameter settings.