Every year, 15 million people worldwide suffer a stroke, resulting in almost six million deaths and five million people left permanently disabled. It occurs when blood supply to the brain is blocked, or a blood vessel bursts. This prevents oxygen reaching the brain and can cause brain cells to die.
Many people who suffer strokes will subsequently experience spasticity, where the arm and leg muscles cramp or spasm as a result of message between the brain and muscle being blocked. This can cause long periods of contraction in major muscles resulting in bent elbows, pointed feet, arms pressed against the chest, or the distinctive curled hand common to many stroke survivors.
Neuroscientists at Newcastle University have developed a new device which aims to help stroke patients by strengthening a spinal connection known as the reticulospinal tract that can take over some of the function of more major neural pathways connecting the brain to spinal cord when they are damaged following a stroke. This strengthening can alleviate the symptoms of spasticity in the hand and arm of patients, allowing them additional control that can help them regain an important degree of independence in their life.
An article published yesterday in the Journal of Neuroscience (1) reports on the early success of this device, which is about the size of a mobile phone and can deliver an audible click followed by a small electric shock to the arm of patients. Electrical stimulation has previously been used to improve nerve function in other types of injury, but the combination with an auditory signal is new. The study shows that the device is able to strengthen the connections in the reticulospinal tract – the nerve tract in the spine which passes messages from the brain to the limb muscles. After a stroke, the body tends to recover the strength of connections to flexor muscles (which allow you to close your hand) more than extensor muscles (which allow you to open your hand). This is why many stroke patients suffer from a curled (semi-closed) hand.
Healthy patients were wired up to receive weak electric shocks to their arm muscle alongside a click sound. The individuals were then sent about their day. By altering the timing of the clicks and shocks they could strengthen or weaken the patients’ reflexes. By wearing the portable electronic device for seven hours, during which time the patients could carry out their daily work, the scientists were able to show that the signal pathways were strengthened in more than half of the patients (15 of 25).
So how did they discover that following a small electric shock with a click could strengthen the nerve pathways between the brain and the arm? Well, it’s a classic case of “Fortune favours the prepared mind”!
Stuart Baker, Professor of Movement Neuroscience at Newcastle University who has led the work said: “We were astonished to find that a small electric shock and the sound of a click had the potential to change the brain’s connections. However, our previous research in primates changed our thinking about how we could activate these pathways, leading to our study in humans.”
In 2012 Baker and his colleagues published a paper reporting on their evaluation of a non-invasive transcranial magnetic stimulation (TMS) in stimulating nerve cells in a part of the brainstem called the reticular formation – where the reticulospinal tract begins – in anaesthetised macaque monkeys, which they undertook as preparation for using TMS in studies in monkeys and human volunteers. They observed that while the TMS stimulus produced a the expected quick response in the nerve cells, they also produced a puzzling delayed response, which they thought might be triggered not by the changes in the magnetic field but rather to the audible click that the TMS making made when its coil discharged. To test this idea they used a miniature bone vibrator to generate the same kind of click, and found that it stimulated a very similar pattern of nerve activation to that evoked by the sound of the TMS coil discharge.
At first they viewed this nerve response to the click sound made by the TMS machine as a complication that needed to be accounted for in future studies of the reticular formation, but very quickly realised that the click response could itself be useful as a non-invasive experimental tool, and might even be useful in the clinic.
Baker wanted to know exactly how much the arm-brain connections were controlled by the reticulospinal pathway they were studying, and determine if the timing of a click following the small electric shock made any difference. To assess this, they got primates to do a similar task to that later evaluated in human volunteers. What they found was that by changing the timing between clicks and small electrical shocks, they could change the strength of reflex of the monkeys by as much as 50%. This has given the researchers the confidence to move this into a clinical trial of stroke patients.
Baker recently published an article on The Conversation entitled “Using monkeys for research is justified – it’s giving us treatments that would be otherwise impossible“. An extract is provided below:
In my own work, we use a small number of macaques to gain this fine-grain understanding. Many pathways for movement control are different between primates such as humans and other animals such as rats. Only a primate model can give us information which is relevant to human diseases.
To learn how these pathways are actually used to control movements, in some studies we first teach the macaque to perform complex tasks with their hands or arm. Getting it right is rewarded with a treat (typically fruit or nuts, but chocolate or strawberry yoghurt also sometimes feature). Once they know what to do, we carry out a surgical implant to allow us to record from the brain using fine electrodes, with tips around the same size as single cells.
All surgery is done in a fully equipped operating theatre, with sophisticated anaesthetics and painkilling medication borrowed from state-of-the-art human care. Once the macaque has recovered, we can record from the brain cells while they do the trained task. An animal that is stressed or in pain would not willingly cooperate with the experiments. The animals seem to enjoy the daily interaction with the lab staff and show no distress.
Our studies are right at the crossroads of basic and clinical sciences. We are trying to understand fundamental brain circuits, and how they change in disease and recovery. Over the past ten years, we’ve shown that a primitive pathway linking brain to spinal cord can carry signals related to hand use. That was a surprise, as until now it was assumed that the primate hand was controlled only by more sophisticated pathways that developed later in evolution.
A clinical trial will now start in Kolkata, India, involving 150 stroke patients. It aims to see whether this new device can improve hand and arm control. The work at Newcastle University has been funded by the Medical Research Council and the Wellcome Trust.
Chris Blower, 30, suffered a stroke at the age of seven, which paralysed him down onside, slurred his speech and caused him to lose bowel control and move unaided. Though he recovered from these immediate effects, he still suffers slow, limited and difficult movement in his right arm and leg. Here is an extract from his story:
My situation is not unique and many stroke survivors have similar long-term effects to mine. Professor Baker’s work may be able to help people in my position regain some, if not all, motor control of their arm and hand. His research shows that, in stroke, the brains motor pathway to the spinal cord is damaged and that an evolutionarily older signal pathway could be ‘piggybacked’ and used instead. With electrical stimulation, exercise and an audible cue the brain can be taught to use this older pathway instead.
This gives me a lot of hope for stroke survivors. My wrist and fingers pull in, closing my hand into a fist, but with the device Professor Baker is proposing my brain could be re-taught to use my muscles and pull back, opening my hand out. The options presented to me so far, by doctors, have been Botox injections and surgery; Botox in my arm would weaken the muscles closing my hand and allow my fingers to spread, surgery would do the same thing by moving the tendons in my arm. Professor Baker’s electrical stimulations is certainly a more appealing option, to me, as it seems to be a permanent solution that would not require an operation on my arm.
Keith toured the animal house at Newcastle University. He noted after:
The macaque monkey that I observed was calmly carrying out finger manipulation tests while electrodes monitored the cells of her spinal cord.
Although this procedure requires electrodes to be placed into the brain and spine of the animal, Professor Baker explained how the monkey had been practising and learning this test for two years before the monitoring equipment was attached. In this way the testing has become routine before it had even started and the animal was in no pain or distress, even at the sight of a stranger (me).
The animals’ calm, placid temperaments carry over to their living spaces; with lots of windows, natural light and high up spaces the macaques are able to see all around them and along the corridors.
It is great to see Newcastle University being clear about the contribution of animal studies to clincal work. In their press release they noted that “the research published today is a proof of concept in human subjects and comes directly out of the team’s work on primates”.
Baker notes in his recent article,” In my opinion, we should not condemn large numbers of people to disability and dependence, but need to use all of the tools of modern science to discover and innovate the solutions. I am confident that the next 50 years will see wonderful progress in treatments for these terrible disorders and primate research will be central to this effort.”
You can read more about animal research at Newcastle University from their website.
Speaking of Research
- K.M. Riashad Foysal, Felipe de Carvalho, Stuart N. Baker. Spike-timing Dependent Plasticity in the Long Latency Stretch Reflex Following Paired Stimulation from a Wearable Electronic Device. Journal of Neuroscience,