Assessing the Reliability of Transcranial Magnetic Stimulation Mapping Using the Pseudorandom Walk Method in the Brachioradialis and the First Dorsal Interosseous Muscles
The scripts provided are relevant for a transcranial magnetic stimulation (TMS) study and can aid in the preprocessing and analysis of the electromyography (EMG) signal.
Background: Transcranial magnetic stimulation mapping of the muscle cortical representations is a valuable tool in clinic and research to measure changes in cortical representations. A common practice to obtain motor maps is to perform the grid mapping technique that is time-consuming and strenuous for patients. Recently, a much faster method, the pseudorandom walk method, has been developed that shows equal reliability compared to grid mapping. However, the reliability has been mainly investigated for hand muscles.
Objective: To examine the reliability of motor maps obtained with the pseudorandom walk of a proximal muscle, the Brachioradialis, and a hand muscle, the First Dorsal Interosseous. Additional objective is to describe the inter-hemispheric differences in motor map parameters of each muscle.
Method: The pseudorandom walk method was used to obtain motor map area, volume, and center of gravity in both muscles. Twenty-two healthy subjects were tested four times over two separate days. Within- and between-session reliability was investigated for the right hemispheric motor map parameters of each muscle and motor map parameters were compared between hemispheres for both muscles.
Results: The right hemispheric motor map parameters of both muscles showed high similarities over all sessions, confirming the reliability of the method to obtain proximal muscle motor maps. No inter-hemispheric differences in motor map parameters of both muscles were observed.
Conclusions: This study extends the reliability of the pseudorandom walk method to the proximal Brachioradialis muscle and brings this technique one step closer to being used in the clinic where patients would benefit greatly.
A) Upper panel: start of the pseudorandom walk method. The experimenter is receiving real-time feedback of the color-coded responses (yellow = max; blue = min). The first 50 pulses are applied in 8 straight lines outward from the hotspot until two consecutive stimuli show no response. The remaining pulses are used to connect the borders of the lines and then pseudorandomly applied within the ellipsoid. Lower panel: end of the pseudorandom walk method. A general trend is observed with higher responses concentrated around the hotspot gradually decreasing towards the borders with zero responses at the borders.
B) EMG signal of the FDI muscle with the baseline activity until 0.1s, the stimulation pulse at 0.1s, and the motor evoked potentials (MEPs) peak time window between 0.115s and 0.15s. EMG responses from all 150 pulses are shown.
C) The coordinates on a plane are shifted and rotated. The MEPs are represented as z-values at their corresponding coordinates and represent the volume of the motor map. The responses are color-coded (yellow = max; blue = min).
Daily supervisor: Carolin Gaiser; Tutors: Prof. Dr. Maarten A. Frens & Prof. Dr. Jos N. van der Geest