We often think of our brains as the centre of complex motor function and control, but how ‘smart’ is your spinal cord? Turns out, it is smarter than we think.
Circuits which travel down the length of our spine control things like the pain reflex in humans and some motor-control functions in animals. Now, new research from Western has shown that the spinal cord is also able to process and control more complex functions, like the positioning of your hand in external space.
“This research has shown that a least one important function is being done at the level of the spinal cord. It opens up a whole new area of investigation to say, ‘What else is done at the spinal level and what else have we potentially missed in this domain?’” said Schulich School of Medicine & Dentistry professor Andrew Pruszynski, the study’s senior and supervising researcher and Canada Research Chair in Sensorimotor Neuroscience.
The study, Spinal stretch reflexes support efficient hand control, supported by Western’s BrainCAN, will be published online in the high impact journal Nature Neuroscience. (LINK to follow)
This kind of hand control requires sensory inputs from multiple joints – mainly the elbow and the wrist. These inputs were previously thought to be processed and converted into motor commands by the brain’s cerebral cortex.
Using specialized robotic technology, a three degree of freedom exoskeleton at Western’s Brain and Mind Institute, subjects were asked to maintain their hand in a target position and then the robot bumped it away from the target by simultaneously flexing or extending the wrist and elbow. The researchers measured the time that it took for the muscles in the elbow and wrist to respond to the bump from the robot and whether these responses helped bring the hand back to the initial target.
By measuring the latency – or ‘lag’ – in the response, they were able to determine whether the processing was happening in the brain or the spinal cord.
“We found that these responses happen so quickly that the only place that they could be generated from is the spinal circuits themselves,” said Schulich postdoctoral scholar Jeff Weiler, the study’s lead researcher, whose work was supported by BrainsCAN. “What we see is, these spinal circuits don’t really care about what’s happening at the individual joints – they care about where the hand is in the external world and generate a response that tries to put the hand back to where it came from.”
This response generated by the spinal cord is called a ‘stretch reflex,’ and has previously been thought to be very limited in terms of how it helps movement.
“Historically, it was believed these spinal reflexes just act to restore the length of the muscle to whatever happened before the stretch occurred,” Pruszynski said. “We are showing they can actually do something much more complicated – control the hand in space.”
This finding adds immensely to our understanding of neuroscience and neurocircuitry, and provides new information and targets for rehabilitation science.
“A fundamental understanding of the neurocircuits is critical for making any kind of progress on rehabilitation front,” said Pruszynski, a scientist at the Robarts Research Institute and Brain and Mind Institute. “Here, we can see how this knowledge could lead to different kinds of training regimens that focus on the spinal circuitry.”