Bashir, ShahidYoo, Woo-KyoungKim, Hyoung SeopLim, Hyun SunRotenberg, AlexanderAbu Jamea, Abdullah2017-05-012017Bashir, Shahid, Woo-Kyoung Yoo, Hyoung Seop Kim, Hyun Sun Lim, Alexander Rotenberg, and Abdullah Abu Jamea. 2017. “The Number of Pulses Needed to Measure Corticospinal Excitability by Navigated Transcranial Magnetic Stimulation: Eyes Open vs. Close Condition.” Frontiers in Human Neuroscience 11 (1): 121. doi:10.3389/fnhum.2017.00121. http://dx.doi.org/10.3389/fnhum.2017.00121.http://nrs.harvard.edu/urn-3:HUL.InstRepos:32630423Objective:: 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.en-USmotor evoked potentialelectromyographymusclestranscranial magnetic stimulationJournal Article2017-05-0110.3389/fnhum.2017.00121