Repetitive peripheral magnetic stimulation to reduce pain or improve sensorimotor impairments: A literature review on parameters of application and afferents recruitment.

INTRODUCTION: Repetitive peripheral magnetic stimulation (rPMS over spinal root, nerve or muscle belly) is a promising technology in physiopathology research. As compared to electrical stimulation, rPMS is deemed to activate deep conductive structures and produce strong muscle contractions and massive proprioceptive afferents with minimal cutaneous recruitment. RPMS may thus act differently on neural plasticity involved in pain reduction and motor recovery in musculoskeletal or neurological conditions. However, literature is very scant and still controversial concerning afferents recruited by rPMS, thus no consensus is reached yet for its clinical use. STUDY AIM: This review dealt with stimulation parameters reported in any scientific research that applied rPMS as an intervention to improve somatosensory or motor disorders with a view of proposing recommendations for future applications. Also, controversy on afferents recruitment was discussed. RESULTS: The literature search resulted in 24 studies. Literature is scant on the topic but our review presents the rationale and the experimental data that may underlie the selection of parameters in future studies using rPMS as an intervention. Although controversy remains, the review presents that the specific recruitment of sensory afferents by magnetic stimulation may offer advantages and disadvantages depending on the pathology. CONCLUSIONS: The review proposed recommendations to improve rPMS application in clinical research. However, the development of guidelines still requires methodological and clinical studies enrolling larger samples and with randomized sham-controlled designs.

Brain control of volitional ankle tasks in people with chronic stroke and in healthy individuals.

This study explored the relationships between motor cortical control of ankle dorsiflexors and clinical impairments of volitional ankle dorsiflexion in people with chronic stroke. Eighteen persons with stroke and 14 controls were evaluated. Clinical tools were used to assess ankle dorsiflexion amplitude and isometric strength. Transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) tested the functional integrity of cortical circuits controlling the tibialis anterior (TA). All clinical scores and most TMS outcomes were impaired in people with chronic stroke. The lower clinical scores were related to the reduction of the strength of corticospinal projections onto spinal motoneurons. Concurrent TMS and clinical testing in chronic stroke provided original data demonstrating relationships between the integrity of cortical and corticospinal components of TA motor control and volitional ankle tasks. Our study proposes that volitional ankle mobilization in chronic stroke may be explained by the residual abnormal M1 circuits which may be responsive for rehabilitation intervention. This should be confirmed in longitudinal studies with larger samples to determine whether TMS outcomes associated with lower limb muscles are predictive of clinical changes or vice versa.

Effects of repetitive peripheral magnetic stimulation on normal or impaired motor control. A review.

INTRODUCTION: Repetitive magnetic stimulation at the periphery (rPMS), i.e. over spinal roots, nerves or muscles, represents a new painless and noninvasive approach that can contribute to motor recovery. This method is based on the assumption that, under rPMS, neural networks involved in motor control would be regulated by the large recruitment of proprioceptive afferents, with little activation of cutaneous receptors. STUDY AIM: This literature review dealing with rPMS after-effects on motor control aimed at better understanding the outcome measures and further discussing some possible involved mechanisms. RESULTS: Our literature search resulted in 13 studies that used different types of outcomes (neurophysiological, biomechanical, clinical) to test the influence of rPMS over spinal roots or muscles in healthy individuals and in persons with stroke or spinal disorders. Dynamic changes were reported post-rPMS, such as spasticity reduction and improvements of movement dynamics. Studies also brought about some interesting insights on the cortical plasticity associated with rPMS effects, such as the activation of fronto-parietal loops that may explain the post-rPMS improvement of motor planning. CONCLUSIONS: Due to the heterogeneous and scant literature on the topic, no conclusion can be drawn to date. However, the results encourage the concurrent testing of clinical, neurophysiological and biomechanical outcomes to investigate more precisely the relevance of rPMS in neurological rehabilitation.