EFFECT OF STIMULUS WAVEFORM ON TRANSCRANIAL MAGNETIC STIMULATION METRICS IN PROXIMAL AND DISTAL ARM MUSCLES
Master of Science
Dr. Carrie Peterson
Dr. Dean Krusienski
Dr. Ravi Hadimani
Objectives: The purpose of this study was to determine the effect of common transcranial magnetic stimulation (TMS) waveforms (monophasic and biphasic) on resting motor threshold (RMT), active motor threshold (AMT), and motor evoked potential (MEP) amplitudes in the biceps and first dorsal interosseous (FDI) because waveforms may affect motor targets differently. Additionally, we determined the test-retest reliability of TMS metrics for each stimulation type and muscle.
Methods: Ten individuals participated in two sessions of single-pulse TMS delivered to the motor cortex perpendicular to the central sulcus. MEPs were normalized to the maximum EMG signal during contraction and were recorded at 120% of RMT, or at 100% of maximum stimulator output (MSO) when RMTs were higher than 84% of MSO.
Results: RMTs and AMTs were lower for monoPA compared to biPA-AP stimulation for the biceps (p<0.01) and FDI (p<0.01). Normalized MEPs were greater for monoPA compared to biPA-AP stimulation in the FDI (p=0.01) and not different in the biceps (p=0.86). Motor thresholds were not different between sessions suggesting high reliability (p<0.01). For both stimulation types, normalized MEPs had very low reliability across sessions in the FDI, and moderate reliability in the biceps.
Discussion: Preliminary investigation shows that current TMS waveform research on upper limb distal muscles is translatable to proximal muscles for motor thresholds but not for MEPs, and test-retest reliability is sensitive to target muscle. These findings can aid future studies in optimizing TMS parameters in order to maximize the efficacy and reliability of TMS for clinical use.
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