Does Voluntary Activity Influence the Effect of Noninvasive Neuromodulation on Corticospinal Excitability in Neurologically Intact Controls and Stroke Survivors with Moderate-to-severe Impairments?

Research Objectives: There are minimal evidence-based interventions to improve hand and finger function in individuals with moderate-to-severe chronic stroke. Noninvasive stimulation techniques have been used to upregulate corticospinal excitability through Hebbian-like plasticity mechanisms, but how this might be achieved in more severely involved cases of stroke is unclear. Here, we examined the effect of paired corticospinal-motor neuronal stimulation (PCMS) synchronized with task practice on corticospinal excitability.

Design: This employed a within-subjects repeated measures design.

Setting: Research laboratory.

Participants: Stroke survivors with moderate-to-severe hand impairment (n=5) and neurologically-intact controls (n=13).

Interventions: Participants participated in three randomized conditions: PCMS with hand muscles at rest (Rest-PCMS), PCMS with hand muscles engaged in task-specific practice (Task-PCMS), and sham stimulation with hand muscles engaged in task-specific practice (Sham-PCMS). Volleys elicited by stimulation of the primary motor cortex and the radial nerve were timed to arrive at corticospinal–motoneuronal synapses during a grasp-and-release task. Functional electrical stimulation (FES) was used to augment muscle activation in stroke survivors. FES was delivered approximately a couple milliseconds after the radial nerve stimulation to assist with the task.

Main Outcome Measures: Changes in the corticospinal excitability (as measured by the motor evoked potential of the extensor digitorum communis muscle) were assessed at baseline, immediately post-interventions, at 15 minutes, and at 30 minutes post intervention.

Results: In controls, Rest-PCMS increased corticospinal excitability immediately (90.39±33%), 15-minutes (54.30±24%), and 30-minutes (66.05±26%) post-intervention. In stroke, Task-PCMS increased corticospinal excitability immediately (50±26%), 15-minutes (60±20%), and 30-minutes (70±32%) post-intervention

Conclusions: Preliminary results indicate that Task-PCMS may have a greater effect on corticospinal excitability in stroke survivors with moderate-to-severe hand impairment. How task repetition, neuromodulation, and neurological status interact to influence corticospinal excitability is unclear but may account in some way for the different response patterns observed between groups. Further work in a larger sample is warranted.

Author(s) Disclosures: No conflicts