Abstract
Evaluation of motor evoked potential (MEP) signals elicited by transcranial magnetic stimulation (TMS) over the motor cortex provide a measure of cortico-motor excitability at the time of stimulation. In the research and clinical medical practice, the MEP latency is a relevant neurophysiological parameter to determine conduction time for neural impulses from the cortex to peripheral muscles. State changes at different levels of signal propagation through the neural tissue can significantly influence MEP latency, based on which different medical diagnoses can be issued. This study aims to present the Squared Hard Threshold Estimator (SHTE), which is a novel and improved algorithm for MEP latency estimation. Analyses presented in the paper were based on the SHTE algorithm, which was efficiently applied to a large number of MEP signals recorded from hand muscles. The SHTE algorithm was compared with other prominent methods such as the absolute hard threshold estimation (AHTE) algorithm, the statistical measures (SM) algorithm, and manual assessment. Results obtained in terms of robustness test and statistical analysis show that the proposed SHTE algorithm is reliable in estimating MEP latency, especially for the MEP signals having peak-to-peak (PTP) amplitudes lower than one hundred microvolts. Compared with the AHTE and SM algorithms, the SHTE shows a lower percentage deviation index in MEP latency estimation of the MEP signals with the PTP amplitudes lower than one hundred microvolts. Hence, the proposed SHTE algorithm represents an improved armamentarium in automatic MEP latency estimation.
Highlights
Since its introduction, which was more than thirty years ago [1], transcranial magnetic stimulation (TMS) has been extensively used as a non-invasive brain stimulation technique to explore cortical physiology in humans
Obtained results show that the Squared Hard Threshold Estimator (SHTE) algorithm had similar achievements in the motor evoked potential (MEP) latency estimation of all MEP signals on the entire amplitude bands level
Compared to other tested algorithms, SHTE has a lower percentage deviation index (PDI) in estimating the MEP latency of the MEP signals with the PTP amplitudes lower than 100 μV (Vpp Vpp < 100 μV)
Summary
Since its introduction, which was more than thirty years ago [1], transcranial magnetic stimulation (TMS) has been extensively used as a non-invasive brain stimulation technique to explore cortical physiology in humans. Single- and paired-pulse TMS protocols applied to the human primary motor cortex (M1) have allowed the physiological investigation of various intracortical inhibitory and facilitatory networks and cortico-cortical connectivity. The nTMS enables three-dimensional (3D) reconstruction of the brain surface based on the positioning of the stimulating coil over the M1 cortex and more precise electromyographic recording of motor evoked potential signals (MEPs) from the target muscles. MEPs elicited by TMS or nTMS over the human motor cortex provides a quantification of cortico-spinal excitability at the time of stimulation [15], [16]. MEPs are interpreted concerning the performance of actions (resting-state vs. execution); secondly, to probe the physiology of the motor cortex
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