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Hering, Philipp (2010): Motorkortikale Erregbarkeit nach repetitiver peripherer Magnetstimulation: Vergleich zweier Stimulationsverfahren. Dissertation, LMU München: Faculty of Medicine
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Abstract

Objective: Transcranial repetitive magnetic stimulation (rMS) is widely used to modulate cortical function. Its potential peripheral use has not been as widely investigated. This study aimed to compare the effectiveness of two different conditioning peripheral rMS protocols in inducing excitability changes in the primary motor cortex in a group of healthy subjects. Methods: Transcranial magnetic stimulation (TMS) of the contralateral primary motor cortex was used to measure motor evoked potentials (MEP), motor recruitment curves (RC), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and the cortical silent period (CSP). These parameters were measured before (pre), immediately after (post) and 30 minutes after (post2) repetitive peripheral magnetic stimulation (rPMS) of the ulnar nerve in the area of the ulnar sulcus. Two different rPMS protocols were compared with control interventions (ipsilateral cortical stimulation). Protocol one was a high-frequency rPMS protocol (HFP: 35 series of stimulation each lasting 1.5 seconds with a frequency of 20 Hz). Protocol two was a low-frequency rPMS protocol (LFP: 15 series each lasting 10 seconds with a frequency of 3 Hz). The control interventions consisted of the same stimulation parameters as the rPMS protocols, but TMS was performed on the ipsilateral (right) primary motor cortex. The evoked MEP were recorded with surface electrodes above the right musculus abductor digiti 5. Results: Both test paradigms caused a significantly longer CSP (LFP: p = 0.015; HFP: p = 0.012) in the post2 measurement. rPMS in the HFP additionally increased CSP duration immediately after the intervention (p = 0.018). Increased MEP amplitudes (p = 0.05) and ICF amplitudes (p = 0.036) and a decrease in SICI (p = 0.008; p = 0.012) were observed only after rPMS in the LFP. The control interventions revealed no consistent significant changes after rPMS. Significance/Discussion: The nearly pain-free rPMS is capable of influencing motor cortical excitability most probably by afferent sensory input. It seems that the duration of the stimulation series is at least as important as the number of stimuli and the stimulation frequency. RPMS with a lower frequency but a longer stimulation series could therefore be a potential alternative to high frequency stimulation in rehabilitative strategies for brain injuries.