Activating motor circuits in the spine
Dr. Patrick Whelan hopes to improve the rehabilitation of patients with spinal cord injury.
Story by Julie Sedivy/Illustration by Mark Gervais
When former Superman actor Christopher Reeve was paralyzed in 1995 after crushing his first and second vertebrae in a riding accident, it was as if the superhero himself had crashed to earth. The news reminded us that even those who seem strong and heroic can be devastated by the effects of spinal cord injury. Paralysis and loss of sensation occur when the nerve cells carrying information to or from the muscles become disconnected from the brain as a result of injury to the back or neck. As a healthy man in the prime of his life, Reeve was a typical victim of spinal cord injury.
Whereas some researchers focus their efforts on regenerating nerve cells in the hope of re-establishing the lost communication with the brain, Dr. Patrick Whelan takes a different tack. It turns out that nerve circuits in the spinal cord send many of the signals that cause muscle contractions during movement . Dr. Whelan is working on getting the most out of these spinal cord circuits, even when they aren't able to communicate with the brain.
A large part of the puzzle consists of discovering how to "turn on" these local spinal cord networks. When the networks' connection to the brain is intact, the brain sends down signals to activate their movement patterns and to regulate the speed of these patterns. Some promising research suggests that certain drugs may eventually be able to play a role in activating the spinal cord networks, replacing some of the function that is lost when the link to the brain is damaged. Dr. Whelan is turning his attention to dopamine, a neurotransmitter produced by the brain that is known best for its effects on mood. Though not commonly associated with spinal cord function, Dr. Whelan has found that dopamine plays a very important role in regulating the spinal centres. "It seems to tweak them in such a way that they produce more robust rhythmic movements." The goal of the research is to study the effects of dopamine in order to understand in detail how these networks function, and how specific cells in the network are turned on to ultimately produce a walking motion.
Although Dr. Whelan's research relies heavily on animal models, he acknowledges that human movement differs in some important ways. By virtue of walking on two legs rather than four, humans have the added complication of needing to keep the body balanced in an upright position while walking, a feat that requires constant and extremely subtle adjustments of posture. Because of this, humans are ultimately more dependent on the connections between the spinal centres and the brain itself.
Despite these differences, Dr. Whelan emphasizes that the similarities between human and animal movement are striking. The actual movement patterns encoded in our spinal cord networks are very similar to those found not only in cats and mice, but also in more primitive animals like lamprey eels. You can see these spinal cord networks in action in the stepping reflex of newborns: a newborn held upright on a flat surface will move one foot in front of the other as if walking.
Rehabilitation of patients with spinal cord injury aims to engage the spinal cord networks, which can be stimulated by movement of the muscles. At first, physiotherapists lift and move the patient's legs to provide more sensory input to the spinal cord network. "The network then changes as a function of the input to better use the information that it's got left," explains Dr. Whelan. Eventually, patients may recover enough function to move the legs on their own, at least to some extent. However, every patient reaches a point where no further improvement occurs. Dr. Whelan hopes that research such as his, which aims to understand how to better activate the networks, will ultimately help patients recover more fully.
Christoper Reeve died in 2004 of complications from his injury. But his legacy lives on through the foundation he created for research on spinal cord injuries—Dr. Whelan has received support for his work from this organization. Could such research someday help those with spinal cord injuries walk again? Dr. Whelan stresses that the combined efforts of researchers from various fields are needed. Recovery of movement by injured patients will involve a combination of rehabilitation to improve the function of spinal cord networks, treatment to regenerate nerves, and early medical intervention to reduce the scope of the injury (for example, by reducing inflammation and scarring). "If you add it all together," Dr. Whelan predicts, "it's probably going to lead to robust change in function."
Did you know?
More than 41,000 Canadians live with spinal cord injury. Approximately 1,200 new injuries occur each year.
The majority (84%) of spinal cord injuries occur in people under the age of 34.
Source: Rick Hansen Institute