When Heather Rendulic experienced a series of strokes in 2012 at the age of 22, she lost functional use of her left hand. A decade later, she is once more able to use a fork and knife, thanks to electrodes implanted in her neck.
About one in four people globally will experience a stroke in their lifetime – a condition in which the blood supply to part of the brain is cut off.
Those who survive are often left with long-term problems including muscle weakness or paralysis, with difficulties around arm and hand movements common. These can have a large impact on those affected, not least in their ability to undertake everyday activities such as eating, writing or getting dressed by themselves.
Now researchers say they have a found a way to restore such movements by stimulating nerve cells inside the spinal cord.
“The most challenging part of my condition is living one-handed in a two-handed world,” said Rendulic. “When the [electrode] stimulation is on, I feel like I now have control of my arm and my hand again that I haven’t had in over nine years.”
Researchers from the University of Pittsburgh and Carnegie Mellon University note that a stroke can lead to disruption of connections between the brain and spinal cord regions that control arm and hand movements.
While some signals from the brain still get through, they are not strong enough to trigger activity in the motor neurons that control movement of the muscles.
Writing in the journal Nature Medicine, the team report how they sought to restore such movement by stimulating the sensory neurons of the muscles that communicate directly with the motor neurons of the limb. When the sensory neurons are stimulated, the motor neurons receive extra excitation, making them more receptive to signals from the brain. In other words, by stimulating the sensory neurons, signals instructing the muscles to move are amplified.
The new study reveals how researchers implanted electrode arrays in Rendulic and another female stroke patient with chronic post-stroke upper-limb weakness.
Dr Douglas Weber, a co-author of the study from Carnegie Mellon University, said the approach was minimally invasive, with an electrode array resembling a spaghetti noodle inserted via a needle such that it sits at the point where the sensory nerves from the limb enter the spinal cord.
The electrodes were left in place for 29 days, with the two participants undergoing four hours of testing a day, five days a week, for a total of four weeks beginning four days after the electrodes were implanted.
The results reveal that when the stimulation was turned on, arm and hand strength improved, as did the range of movements the participants could make.
“Stimulation feels kind of like a tickle and it’s never painful, but it takes some getting used to, I would say,” said Rendulic.
“It’s just awesome because I can move my arm and hand in ways that I haven’t done in almost a decade.”
The stimulation also enabled the participants to complete a number of tasks they would otherwise have struggled with, including opening a lock, drawing a spiral, eating with a fork and completing reaching and moving tasks.
“From the patient’s perspective, it’s easier to move the arm again … the arm is actually responding to what they are intending it to do. Whereas without stimulation and after the stroke, it requires a great deal of effort to do even simple tasks,” said Weber.
Dr Elvira Pirondini, another author of the study, said the technology leveraged the natural mechanisms for movement meaning that, at least for simple tasks, training was not needed. “Immediately from day one, the subject could already attempt some movement,” she said.
The research also reveals that both participants showed some lasting improvements in motor function by the final week of the study that were present even without the stimulation turned on.
The research is not the first time that stimulation of the spinal cord has transformed the lives of people with paralysis: scientists have previously used a similar approach to enable paraplegic patients to walk once again.
Pirondini speculated that while stroke patients with mild impairments may require the implanted electrodes for a shorter period, those with more severe impairments may always need the technology.
