Sending electrical impulses down the longest nerve in the human body has shown ‘great success’ in amplifying the effects of motor rehabilitation post-stroke.
The longest nerve in the human body starts in the brain and works its way down the neck and into the chest, where it splits into separate branches, winding its twisting tendrils to touch each internal organ.
Known as the “information superhighway,” the vagus nerve is a bundle of fibres responsible for the parasympathetic nervous system: breathing, heart rate, digestion.
Sending electrical impulses down this tenth cranial nerve has proven effective in treating conditions like depression and epilepsy, and has now shown great success in amplifying the effects of motor rehabilitation post-stroke.
Implanting a device onto the vagus nerve in the neck provides direct stimulation to the vagus nerve. Using this technology during post-stroke motor rehabilitation was approved by the Food and Drug Administration as a treatment option in 2021.
However, researchers at MUSC believe they have found another method that speeds up treatment outcomes and improves motor function after stroke without this invasive procedure.
As described in a recent paper from Neurorehabilitation and Neural Repair, the research team placed sensors on the upper arm and in the ear and used the connected computer to send timed electrical impulses to the vagus nerve during motor rehabilitation.
This noninvasive VNS method, known as motor activated auricular vagus nerve stimulation (MAAVNS), allows stroke survivors to gain the same amount of motor function improvement in 4 weeks that stroke survivors with the implanted device reached in 6 weeks – all without surgery.
MAAVNS was developed and is currently pending patent at MUSC.
Principal investigator of this study, Bashar Badran, says: “Motor rehabilitation is time-consuming and expensive, and oftentimes does not produce the results that patients want.
“Technology like the MAAVNS system can boost the effects of conventional motor rehabilitation and help patients get the most out of their therapy in a simple and relatively inexpensive manner. It’s very exciting.”
With a small cart containing the computer and sticker-like sensors, the MAAVNS system can easily be incorporated into occupational therapy settings, with little change or impact to the current standard of care.
With hundreds of repetitions in an hour, patients can focus on specific movements they want to improve, like sewing, cutting fabric or buttoning a shirt, while the MAAVNS system detects when the patient is moving and intricately delivers electrical stimulation to nerves in the ear.
Badran says delivering the stimulation in conjunction with each movement is critical. “Our work shows that outcomes are much better when you time the stimulation in conjunction with movement, in a closed-loop approach.
“Interestingly, more stimulation is not better. In fact, less stimulation timed correctly produces the best outcomes.”
Since the vagus nerve elicits brain activity in areas responsible for the release of neurotransmitters like norepinephrine and serotonin which help the brain learn, stimulating it with electricity facilitates faster learning of motor skills.
