Abstract
Stimulating the nervous system and measuring muscle response offers a unique opportunity to interrogate motor system function. Often, this is performed by stimulating motor cortex and recording muscle activity with electromyography; the evoked response is called the motor evoked potential (MEP). To understand system dynamics, MEPs are typically recorded through a range of motor cortex stimulation intensities. The MEPs increase with increasing stimulation intensities, and these typically produce a sigmoidal response curve. Analysis of MEPs is often complex and analysis of response curves is time-consuming. We created an MEP analysis software, called Motometrics, to facilitate analysis of MEPs and response curves. The goal is to combine robust signal processing algorithms with a simple user interface. Motometrics first enables the user to annotate data files acquired from the recording system so that the responses can be extracted and labeled with the correct subject and experimental condition. The software enables quick visual representations of entire datasets, to ensure uniform quality of the signal. It then enables the user to choose a variety of response curve analyses and to perform near real time quantification of the MEPs for quick feedback during experimental procedures. This is a modular open source tool that is compatible with several popular electrophysiological systems. Initial use indicates that Motometrics enables rapid, robust, and intuitive analysis of MEP response curves by neuroscientists without programming or signal processing expertise.
Highlights
To assay the descending motor system, muscle responses to motor cortex stimulation are measured as the motor evoked potential (MEP) using electromyography (EMG)
We present the methods by which we compare recruitment curves obtained from different experimental conditions
MEPs for recruitment curves were recorded under different conditions: Baseline and spinal cord stimulation applied 9, 10, or 11 ms after cortical stimulation
Summary
To assay the descending motor system, muscle responses to motor cortex stimulation are measured as the motor evoked potential (MEP) using electromyography (EMG). A characteristic of MEPs is that as stimulation strength is gradually increased, the MEP increases exponentially, exhibits a linear relationship, and begins to saturate as stimulation intensity is increased (Devanne et al, 1997; Boroojerdi et al, 2001; Luft et al, 2001). This gives an “S” or sigmoid curve to the plot of stimulus intensity vs MEP. This characteristic curve is known as the recruitment curve as it describes indirectly, the MEP obtained by “recruiting” motor units (Fuglevand et al, 1993).
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