Changes in muscle responses to stimulation of the motor cortex induced by peripheral nerve stimulation in human subjects

Abstract

The aim of this study was to determine whether prolonged, repetitive mixed nerve stimulation (duty cycle 1 s, 500 ms on-500 ms off, 10 Hz) of the ulnar nerve leads to a change in excitability of primary motor cortex in normal human subjects. Motor-evoked potentials (MEPs) generated in three intrinsic hand muscles [abductor digiti minimi (ADM), first dorsal interosseous (FDI) and abductor pollicis brevis (APB)] by focal transcranial magnetic stimulation were recorded during complete relaxation before and after a period of prolonged repetitive ulnar nerve stimulation at the wrist. Transcranial magnetic stimuli were applied at seven scalp sites separated by 1 cm: the optimal scalp site for eliciting MEPs in the target muscle (FDI), three sites medial to the optimal site and three sites lateral to the optimal stimulation site. The area of the MEPs evoked in the ulnar-(FDI, ADM) but not the median-innervated (APB) muscles was increased after prolonged ulnar nerve stimulation. Centre of gravity measures demonstrated that there was no significant difference in the distribution of cortical excitability after the peripheral stimulation. F-wave responses in the intrinsic hand muscles were not altered after prolonged ulnar nerve stimulation, suggesting that the changes in MEP areas were not the result of stimulus-induced increases in the excitability of spinal motoneurones. Control experiments employing transcranial electric stimulation provided no evidence for a spinal origin for the excitability changes. These results demonstrate that in normal human subjects the excitability of the cortical projection to hand muscles can be altered in a manner determined by the peripheral stimulus applied.

<b>The impact of high-frequency magnetic stimulation of peripheral nerves: muscle hardness, venous blood flow, and motor function of upper extremity in healthy </b><b>subjects </b>

“…There is a report that confirmed the sustained cortical excitability 15 min after peripheral nerve electrical stimulation with transcranial magnetic stimulation-elicited MEPs (16), and this particular finding was considered to be one of the reasons why the effects of stimulation were sustained in our study. In the future, it will be necessary to also investigate the duration of stimulation effects in each type of measurement.…”

Time course of motor excitability before and after a task-related movement

“…4). In theory, this increase in probability may result from (a) an increase in excitability of the motor cortex related to the preparation for the movement and inputs from associated structures such as the supplementary motor area and premotor cortex; (b) disinhibition of motor cortex by otherwise ineffective or weak synapses becoming disinhibited ("unmasked") such that they influence cortical activity [20,26]; or (c) increased sub-cortical excitability at the spinal level. Spinal contribution to excitability changes may be due to corticofugal influences before movement or to afferent inputs following the movement.…”

“…Spinal facilitation has been demonstrated only between 50 and 100 ms before EMG onset [6,11] and thus cannot explain the excitability changes beyond this time period. The effect of afferent inputs after movement is unlikely because afferent inputs have been shown not to affect spinal motoneuron or interneuron excitability [20].…”

Activation of Brain Sensorimotor Network by Somatosensory Input in Patients with Hemiparetic Stroke: A Functional MRI Study

“…Peripheral nerve stimulation increases corticomotoneuronal excitability Ridding et al, 2000), and activation of S1M1 and PMd in healthy subjects (Wu et al, 2005). If applied to paretic hand of stroke patients paired with motor training, electrical nerve stimulation may enhance training effects on corticomotoneuronal plasticity in stroke patients (Sawaki et al, 2006;Yozbatiran et al, 2006;Celnik et al, 2007).…”