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Front Hum Neurosci. 2017 Mar 21;11:121. doi: 10.3389/fnhum.2017.00121. eCollection 2017.

The Number of Pulses Needed to Measure Corticospinal Excitability by Navigated Transcranial Magnetic Stimulation: Eyes Open vs. Close Condition.

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Department of Physiology, Faculty of Medicine, King Saud UniversityRiyadh, Saudi Arabia; Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical SchoolBoston, MA, USA.
Department of Physical Medicine and Rehabilitation Medicine, Hallym University Sacred Heart HospitalSeoul, South Korea; Hallym Institute for Translational Genomics and Bioinformatics, Hallym University College of MedicineSeoul, South Korea.
Department of Physical Medicine and Rehabilitation, National Health Insurance Ilsan Hospital Seoul, South Korea.
Neuromodulation Program, Division of Epilepsy and Clinical Neurophysiology, Department of Neurology and the F.M. Kirby Neurobiology Center, Boston Children's Hospital Boston, MA, USA.
Department of Radiology and Medical Imaging, College of Medicine, King Saud University Riyadh, Saudi Arabia.


Objective: Motor evoked potentials (MEPs) obtained by transcranial magnetic stimulation (TMS) enable measures of the corticospinal excitability (CSE). However the reliability of TMS-derived CSE measures is suboptimal due to appreciable pulse-to-pulse MEP amplitude variability. We thus calculated how many TMS-derived MEPs will be needed to obtain a reliable CSE measure in awake adult subjects, in the eyes open (EO) and eyes closed (EC) conditions. Methods: Twenty healthy adults (70% male) received 40 consecutive navigated TMS pulses (120% resting motor threshold, RMT) in the EO or EC conditions on two separate days in randomized order. Results: For either the EO or EC condition, the probability that the 95% confidence interval (CI) derived from consecutive MEP amplitude measured included the true CSE, increased when the number of consecutive stimuli increased (EO: p = 0.05; EC: p = 0.001). No significant effect of RMT, Mini-Mental State Examination (MMSE) score, or gender on the CSE estimates was identified. At least 34 consecutive stimuli were required to obtain a most reliable CSE estimate in the EO condition and 31 in the EC condition. Conclusion: Our findings indicate that >30 consecutive MEPs may be necessary in order to obtain a CSE measure in healthy adults.


electromyography; motor evoked potential; muscles; transcranial magnetic stimulation

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