Vagus Nerve Stimulation Accelerates Stroke Recovery

Researchers at the University of Texas at Dallas (UTD; Richardson, USA) and the Texas Biomedical Device Center (TxBDC; Richardson, USA) conducted a study in rats to determine if VNS could promote generalization, long-lasting recovery, and structural plasticity in motor function after stroke. The rats were first trained on a fully automated, quantitative task that measures forelimb supination. Once the rats achieved task proficiency, unilateral cortical and subcortical ischemic lesions were administered.

One week later, the rats were randomly assigned to receive a total of six weeks of rehabilitative training on the learned supination task, with or without VNS. The rats additionally underwent four weeks of testing to assess forelimb strength as an indicator of generalization of recovery. The durability of VNS benefits were also tested on the supination task two months after cessation of VNS, with viral tracing performed in order to assess synaptic connectivity in motor networks.

The results revealed that VNS enhanced plasticity in corticospinal motor networks, with a threefold-to-fivefold increase in the number of engaged neurons. Synaptic connectivity to the musculature of the rehabilitated forelimb was also enhanced, more than doubling the benefit of rehabilitative training. The researchers also found that pairing VNS with supination training in previously unknown tasks resulted in significantly improved volitional forelimb strength, suggesting generalization of forelimb recovery. The study was published on January 25, 2018, in Stroke.

“Our experiment was designed to ask this new question: After a stroke, do you have to rehabilitate every single action? If VNS helps you, is it only helping with the exact motion or function you paired with stimulation?” said study co-author Michael Kilgard, MD, associate director of TxBDC. “What we found was that it also improves similar motor skills as well, and that those results were sustained months beyond the completion of VNS-paired therapy. If we use this approach on complicated motor skills, those improvements can filter down to improve simpler movements.”

“If you have a stroke, you may have a limited time with a therapist. So when we create guidelines for a therapist, we now know to advise doing one complex activity as many times as possible, as opposed to a variety of activities,” said senior author Seth Hays, PhD, director of preclinical research at TxBDC. “That was an important finding; it was exciting that not only do we improve the task that we trained on, but also relatively similar tasks. You are getting generalization to related things, and you're getting sustained improvement months down the line.”

The vagus nerve is the tenth cranial nerve, and interfaces with parasympathetic control of the heart, lungs, and digestive tract. It is the longest nerve of the autonomic nervous system, supplying motor parasympathetic fibers to all the organs (except the adrenal glands), from the neck down to the second segment of the transverse colon. It also innervates several skeletal muscles, including the cricothyroid, the superior, middle and inferior pharyngeal constrictors, and other muscles of the pharynx and larynx, thus controlling muscle movements in the mouth and speech.

Related Links:
University of Texas at Dallas
Texas Biomedical Device Center