Repetitive common peroneal nerve stimulation increases ankle dorsiflexor motor evoked potentials in incomplete spinal cord lesions

Abstract

Plasticity of corticospinal tract (CST) activity likely plays a key role in motor function recovery after central nervous system (CNS) lesions. In non-injured adults, 30 min of repetitive common peroneal nerve stimulation (rCPnS) increases CST excitability by 40-50% and the effect persists for at least 30 min. The present study evaluated with transcranial magnetic stimulation (TMS) the changes in CST excitability after 30 min of rCPnS in people with foot drop due to incomplete SCI. Suprathreshold rCPnS (25 Hz, alternating 1 s on 1 s off stimulation cycle) was given for two 15-min periods, while the subject sat at rest with ankle and knee joints fixed. Before, between, and after the periods of stimulation, the tibialis anterior (TA) motor evoked potentials (MEPs) to TMS were measured at a TMS intensity that originally produced a half-maximum MEP (typically 10-20% above threshold) while the sitting subject provided 25-30% maximum voluntary TA contraction. In 10 subjects with SCI, the peak-to-peak TA MEP increased by 14 ± 3% after rCPnS and the peak increase (+21 ± 7%) occurred 15 min after the cessation of rCPnS. The TA H-reflex, measured in separate experiments in 7 subjects, did not increase after rCPnS. The results indicate that rCPnS can increase CST excitability for the TA in people with incomplete SCI, although its effects appear smaller and shorter lasting than those found in non-injured control subjects. Such short-term plasticity in the CST excitability induced by rCPnS may contribute to long-term therapeutic effects of functional electrical stimulation previously reported in people with CNS lesions.

The effect of timing electrical stimulation to robotic-assisted stepping on neuromuscular activity and associated kinematics

“…Some studies have shown that patterned stimulation alone, comparable with what was used in the RS group, can improve corticospinal excitability, which in turn is linked to enabling rehabilitation in patients with SCI [28][29][30]32]. The present study demonstrates that coordinating FES with treadmill training in animals with SCI leads to better functional outcome than FES alone.…”

“…There is evidence that patterned stimulation alone, i.e., not timed with afferent feedback, was sufficient to induce short-term plasticity in the spinal circuitry [29][30]62]. A single session of FES of the CPN was sufficient to enhance excitation in the corticospinal pathways controlling the TA in nondisabled subjects [30] and subjects with SCI [29].…”

“…A single session of FES of the CPN was sufficient to enhance excitation in the corticospinal pathways controlling the TA in nondisabled subjects [30] and subjects with SCI [29]. In these studies, FES was applied while the subjects were seated and the maximal effects were observed 40 to 45 min poststimulation.…”

“…More recent findings suggest that the therapeutic effect of FES may be mediated by a strengthening of corticospinal connections to ankle dorsiflexor muscles such as the tibialis anterior (TA) [21,27]. There is evidence that repetitive FES alone (i.e., stimulation that is not paired with movement but applied while subjects were seated) can modulate corticospinal circuits controlling ankle dorsiflexion [28][29][30][31]. For example, motor-evoked potentials in the TA were increased by 30 min of repetitive stimulation of the common peroneal nerve (CPN) in subjects with SCI [29].…”

“…There is evidence that repetitive FES alone (i.e., stimulation that is not paired with movement but applied while subjects were seated) can modulate corticospinal circuits controlling ankle dorsiflexion [28][29][30][31]. For example, motor-evoked potentials in the TA were increased by 30 min of repetitive stimulation of the common peroneal nerve (CPN) in subjects with SCI [29]. Stimulating the CPN during voluntary ankle flexion further increases motor cortical excitability [32].…”