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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.

Author information

1
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.
2
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.
3
Department of Physical Medicine and Rehabilitation, National Health Insurance Ilsan Hospital Seoul, South Korea.
4
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.
5
Department of Radiology and Medical Imaging, College of Medicine, King Saud University Riyadh, Saudi Arabia.

Abstract

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.

KEYWORDS:

electromyography; motor evoked potential; muscles; transcranial magnetic stimulation

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