Abstract
This study examines with transcranial magnetic stimulation (TMS) and with functional magnetic resonance imaging (fMRI) whether 20 min of repetitive peripheral magnetic stimulation (rPMS) has a facilitating effect on associated motor controlling regions. Trains of rPMS with a stimulus intensity of 150% of the motor threshold (MT) were applied over right hand flexor muscles of healthy volunteers. First, with TMS, 10 vs. 25 Hz rPMS was examined and compared to a control group. Single and paired pulse motor evoked potentials (MEPs) from flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles were recorded at baseline (T0), post rPMS (T1), 30 min post (T2), 1 h post (T3) and 2 h post rPMS (T4). Then, with fMRI, 25 Hz rPMS was compared to sham stimulation by utilizing a finger tapping activation paradigm. Changes in bloodoxygen level dependent (BOLD) contrast were examined at baseline (PRE), post rPMS (POST1) and 1 h post rPMS (POST2). With TMS facilitation was observed in the target muscle (FCR) following 25 Hz rPMS: MEP recruitment curves (RCs) were increased at T1, T2 and T3, and intracortical facilitation (ICF) was increased at T1 and T2. No effects were observed following 10 Hz rPMS. With fMRI the BOLD contrast at the left sensorimotor area was increased at POST1. Compared to inductions protocols based on transcutaneous electrical stimulation and mechanical stimulation, the rPMS induced effects appeared shorter lasting.
Highlights
It is well known that a period of afferent stimulation is able to facilitate corticomotor excitability, and to induce outlasting neuromodulatory effects within the sensorimotor cortex
Effect of repetitive peripheral magnetic stimulation (rPMS) on motor evoked potentials (MEPs) Recruitment Curves MEP recruitment curves (RCs) are presented on Figure 2
From the transcranial magnetic stimulation (TMS) assessments an increase in corticomotor excitability was found after rPMS with a rate of 25 Hz, and in the subsequent functional magnetic resonance imaging (fMRI) assessment short lasting focal activations within the sensorimotor cortex were detected
Summary
It is well known that a period of afferent stimulation is able to facilitate corticomotor excitability, and to induce outlasting neuromodulatory effects within the sensorimotor cortex Such effects had been shown following trancutaneous electrical stimulation (TES), at stimulation intensities either above motor threshold (MT; Ridding et al, 2000), below MT but above sensory level (Hamdy et al, 1998), or even at stimulation intensities below sensory level (Golaszewski et al, 2004), see Chipchase et al (2011) for review. If compared to TES, the magnetic field induced eddy currents penetrate into deeper tissue regions (Barker, 1999), activating fast conducting proprioceptive and somatic nerve structures (Behrens et al, 2011) To this muscle contractions induced by rPMS are recognized as less painful (Bischoff et al, 1994), supporting evidence that axons from superficial pain receptors became less excited (Struppler et al, 1996). Concerning the induction of cortical plasticity, comparable effects are expected with rPMS
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