Depending on the degree of impairment, motor rehabilitation training led by a trained therapist is ... [+]
According to the CDC, someone in the United States experiences a stroke every forty seconds. Sometimes referred to as a “brain attack,” a stroke occurs when blood flow to the brain is interrupted or reduced. The subsequent damage to affected brain tissues can generate significant deficits, especially in motor function. In fact, approximately 85% of stroke cases struggle to retain function in the upper extremities, resulting in reduced quality of life.
Depending on the degree of impairment, motor rehabilitation training led by a trained therapist is the most effective therapy for helping individuals regain lost skills. Traditional motor rehabilitation usually involves practicing repetitive task-oriented movements to stimulate motor learning. Unfortunately, for some, the benefits of these training sessions are not enough to overcome motor deficits. Now, studies suggest that coupling rehabilitative therapy with vagus nerve stimulation may enhance outcomes.
The vagus nerve connects the brain to the rest of the body. Bidirectional communication enables the brain to send signals down to our muscles and receive sensory inputs from all around the body. As a result, the vagus nerve is involved in nearly every bodily function. Previously in this series on the vagus nerve, we reported on the benefits of vagal nerve stimulation in reducing chronic inflammation by stimulating the brain to recruit anti-inflammatory factors. Emerging studies now report that electrically stimulating this nerve during motor training sessions can nearly double the rehabilitative benefits, compared to motor training alone. In fact, the FDA has already approved the use of implanted vagal nerve stimulation devices during motor rehabilitation.
Cutting-edge approaches to stimulating the vagus nerve offer a new non-invasive method for treating strokes. Known as transcutaneous auricular vagus nerve stimulation, individuals simply wear removable earpieces that generate signals through the ear canal. The major benefit of this new technology is that it can be calibrated to deliver electrical stimulation precisely at the onset of movement. To do so, a team from South Carolina developed a closed-loop system in which electromyography (EMG) electrodes record impulses in the upper arm muscles and signal to a transcutaneous auricular vagus nerve device. When enough signals are detected beyond a particular threshold, the vagus nerve is stimulated. This allows stimulation to be perfectly timed with movement, removing the responsibility of an occupational therapist to monitor movement and deliver the stimulation. Badran et. al recently published the findings from their pilot study in Neurorehabilitation and Neural Repair, suggesting that the benefits of this innovative approach may be just, if not more, beneficial than traditional vagus nerve stimulation methods.
Twenty participants that had experienced a stroke within the past six months were recruited for this study. The cohort was equally divided into two groups: the experimental group received low levels of electrical stimulation to both ears simultaneous with arm movement, while the others received stimulation at regular intervals regardless of movement. Blinded to their assigned group, all the participants were equipped with electrodes to track muscle movement, even if it was not paired with electrical stimulation.
The participants completed a total of twelve motor rehabilitation sessions over the span of four weeks, during which they completed task-specific training. Guided by a trained occupational therapist, these tasks targeted upper motor function and increased in difficulty over time. Motor improvement was subsequently assessed based on the Fugl-Meyer Upper Extremity Assessment, a standardized tool for measuring upper extremity impairment, and the Wolf Motor Function Test, which quantifies upper arm function across different types of tasks.
Even though the group receiving vagal nerve stimulation at regular intervals received more electrical inputs, there were no significant differences between the groups. Both demonstrated considerable improvement in motor function after completing the sessions. Post hoc analysis, however, did reveal that the paired movement and stimulation group had a much greater effect size, suggesting that improvements may have been more consistent across those participants.
How does this approach compare to current FDA-approved implanted vagal nerve stimulation? Although this study did not directly compare invasive vs. non-invasive approaches, Badran et. al is confident that their findings are comparable to those from clinical trials with implanted stimulation devices. In fact, it is promising that non-invasive transcutaneous auricular vagus nerve stimulation can generate improvements in motor function in twelve weeks which normally takes eighteen sessions to experience with implanted methods.
A stroke can result in devastating damage to neural tissue that can lead to lifelong disability. This novel treatment regimen offers a less invasive, more accessible option for those affected. Although repairing damaged brain tissue may be impossible, stimulating the vagus nerve may at least be able to reduce deficits and improve quality of life.
