Rachel’s pet kitten pads its way gently to her side, brushing its warm furry body against her legs. “Hello there…” Rachel coos, as her gaze meets those innocent eyes of the kitten glistening like black pearls. The kitten then yawns and stretches, before heading off to explore some nook in Rachel’s house. Rachel misses the warm furry feeling against her leg, as with her spinal cord injury, her bottom torso is unable to feel anything.
Have you ever experienced your arm “falling asleep”? Trapped under your pillow during your nap, you wake up with your arm feeling numb, before some amount of shaking it around brings pain and needles, but at least your arm can feel now to your relief.
Unfortunately, like Rachel, people afflicted with paralysis cannot just shake away their problem. Paralysis occurs when there is complete loss of muscle function, often together with sensory loss due to damaged brain to muscle/sensory nerve connections or damaged part of the brain controlling specific muscles. Signals from brain to muscle cannot be relayed, and the person is thus unable to move the affected area. About 1 in 50 people worldwide are afflicted with paralysis. The most common cause is from stroke, followed by spinal cord injury, and other causes like head injury or multiple sclerosis. All these affect the central nervous system (CNS), which consists of the brain and spinal cord, which runs along the brain, neck and spine.
Besides being unable to move and have a sense of feeling in the afflicted area, many experience muscle stiffness (termed medically as muscle spasticity) as well. Nerves below the injured area misfire, causing involuntary muscle spasms. Depending on the site of injury especially for spinal cord injuries, the severity of paralysis varies. Injuries higher up the spinal cord like a broken neck normally induce paralysis in both arms and legs and breathing difficulties. Loss of bowel and bladder control is also commonly experienced. Unfortunately, our CNS cannot heal itself unlike other organs and tissues. Some cells of the CNS are too specialised to regenerate new cells. Furthermore, damaged cells trigger an inflammation response and release of free radicals that further damage neurons and supporting cells in the spinal cord. One can imagine the inconvenience that paralysis brings about in going about daily activities independently. Although a paralysed person can utilise mobility aids, scientists have been working on biotechnologies that may provide more permanent solutions to paralysis. Some of the promising ways to reverse paralysis include epidural spinal stimulation, which may reprogram damaged spinal nerves to be able to receive signals once again; and stem cell regeneration of spinal nerves and supporting cells.
One of the exciting breakthroughs so far is a neural prosthetic implanted in the brain, where it transmits the patient’s thoughts into signals wirelessly detected by electrical stimulators placed near the area of injury. Assuming some neural connections are still left intact after paralysis, this prosthetic allows neural signals to bypass the spine to control the paralysed muscle directly. Grégoire Courtine’s laboratory in Wyss Centre for Bio and Neuroengineering, Geneva successfully restored the ability of their experimental subject – a macaque monkey paralysed in its right leg, to walk again through installing a recording device touching its motor cortex and stretchable electrodes around its spinal cord below the site of injury. The device, smaller than a stamp and made of silicon with many metal ‘hair-like’ probes, managed to capture the monkey’s thoughts of walking, and then transmitted it as an electrical stimulation to the spine, allowing its right leg to move.
Courtine, a French neuroscientist remarked, “Just try sitting on your hands for a day. That will give you an idea of the shattering consequences of spinal cord injury. You can’t scratch your nose or tousle a child’s hair. But if you have this, it changes your life.”
This neural bypass was tested in a quadriplegic man as well by researchers from Case Western Reserve University. Helmed by Robert Kirsch and Bolu Ajiboye, the scientists inserted 16 electrodes into the man’s hand and arm muscles, which received signals from a recording implant in his brain. Amazingly, he could raise a cup to his mouth with the aid of a spring-loaded arm rest, and open and close his hand.
With further research still to be done, it is estimated that this biotechnology is still 10-15 years away though. Meanwhile, improved prototypes of the wireless recording device have been developed, including one matchbox-sized version, made of biocompatible titanium. Head of the Wyss Centre, John Donoghue aims for a device that occupies the least volume and able to record brain signals at top speeds. He terms it “a neurocomm, a radio inside your head…the most sophisticated brain communicator in the world.” Besides size and speed, scientists have to ensure biocompatibility of the neural implant with neural tissue to prevent tissue tearing or infection.
Despite slow progress due to the complexity of neural connections, Donoghue believes neural prosthetics are worth the investment in research. “Ask someone if they would like to move their own arm. People would prefer to be restored to their everyday self. They want to be reanimated.”
by Cheryl Lee Zhi Qin
Cheryl likes to write and learn new things, especially in public health issues and science. She hopes to travel to as many countries as possible.