Peripheral electrical stimulation to induce cortical plasticity: A systematic review of stimulus parameters

Abstract

Peripheral electrical stimulation (ES) is commonly used as an intervention to facilitate movement and relieve pain in a variety of conditions. It is widely accepted that ES induces rapid plastic change in the motor cortex. This leads to the exciting possibility that ES could be used to drive cortical plasticity in movement disorders, such as stroke, and conditions where pain affects motor control. This paper aimed to critically review the literature to determine which parameters induced cortical plasticity in healthy individuals using ES. A literature search located papers that assessed plasticity in the primary motor cortex of adult humans. Studies that evaluated plasticity using change in the amplitude of potentials evoked by transcranial magnetic stimulation of the motor cortex were included. Details from each study including sample size, ES parameters and reported findings were extracted and compared. Where data were available, Cohen's standardised mean differences (SMD) were calculated. Nineteen studies were located. Of the parameters evaluated, variation of the intensity of peripheral ES appeared to have the most consistent effect on modulation of excitability of corticomotor pathway to stimulated muscles. There was a trend for stimulation above motor threshold to increase excitability (SMD 0.79 mV, CI -0.10 to 1.64). Stimulation below motor threshold, but sufficient to induce sensory perception, produced conflicting results. Further studies with consistent methodology and larger subject numbers are needed before definitive conclusions can be drawn. There also appeared to be a time effect. That is, longer periods of ES induced more sustained changes in cortical excitability. There is insufficient evidence to determine the effect of other stimulation parameters such as frequency and waveform. Further research is needed to confirm whether modulation of these parameters affects plastic change.

Evaluation of the neuromuscular compartments in the peroneus longus muscle through electrical stimulation and accelerometry

“…Interventions based on electrical principles take advantage of the physiological characteristics of muscles and nerves to generate therapeutic effects. One of these characteristics is the motor threshold (MT), which is defined as the minimum intensity at which a visible and palpable contraction of the muscle is obtained 20 . The MT varies between muscles and subjects and is used as a reference for localizing motor points.…”

Tactile stimulation interventions: Influence of stimulation parameters on sensorimotor behavior and neurophysiological correlates in healthy and clinical samples

“…Concerning the motor threshold, TENS had no effect, regardless of the applied intensity in either the healthy population (Chipchase et al, 2011;Kaelin-Lang et al, 2002;Mima et al, 2004;Ridding et al, 2000) or patients with subacute stroke (Celnik et al, 2007). One PARAMETER CHOICE AND EFFECTIVENESS OF TACTILE STIMULATION 58 protocol applying motor stimulation at 0.67 Hz frequency on average for 1 hour in 9 sessions, prior to motor training could not affect either motor threshold, MEP amplitudes or recruitment curves (McDonnell et al, 2007), which might be due to the relatively low frequency and stimulation time.…”

“…This supports different effects of stimulation with regard to the cortex as opposed to the corticomotor pathway. To explain the stronger effect of stimulation at motor intensity on MEPs, Chipchase and colleagues (2011) further proposed that stimulation at motor intensity is able to induce changes in other groups of the motor cortical pathway, including muscle fibers and motorspinal neurons, but stimulation at sensory intensities might have a larger effect in exciting also antagonist muscles (Chipchase et al, 2011). Besides they suggested that also differences between the corticobulbar and corticospinal pathway might play a role in the variable effects of stimulation at motor and suprasensory intensities.…”

Paired associative stimulation after spinal cord injury: Who should undergo?

“…5 A well-known method to stimulate lower motor neurons is peripheral nerve stimulation (PNS) which has been used mostly to prevent muscular and axonal atrophy in paretic limbs. [6][7][8] For upper neuros, it is transcranial magnetic stimulation (TMS) of the corresponding motor cortex. 9 Applied together, PNS and TMS are called paired associative stimulation (PAS) and are believed to strengthen excitatory synapses and inducing neural plasticity.…”