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It is well known that neural circuits in the spinal cord control seemingly simple things like the reflex of pain in humans and some motor control functions in animals. Now, a new study published in the journal Nature Neuroscience has shown that the spinal cord is also able to process and control more complex functions, such as positioning your hand in an outdoor space.
Weiler et al show that, for postural control of the hand, even the fastest feedback path of the spine can produce effective corrective responses, which requires rebadessing how the nervous system derives control laws that support behavior engine. Image credit: Medium69 / Jmarchn.
"Our research has shown that at least one important function is performed at the level of the spinal cord and this opens up a whole new field of investigation: say: what more do we do at the level of the spinal column and what is potentially missed? this domain? Said lead co-author Dr. Andrew Pruszynski, a researcher at Western University in London, Ontario, Canada.
"This type of hand control requires sensory input from multiple joints – mainly the elbow and wrist – and it was previously thought that these inputs were processed and converted into motor commands by the cerebral cortex of the brain."
With the help of a specialized robotic technology, an exoskeleton with three degrees of freedom, subjects were asked to hold their hand in the target's position, and then the robot moved away from the target. target by flexing or extending the wrist and elbow simultaneously.
Dr. Pruszynski and his colleagues measured how long it took for the elbow and wrist muscles to respond to the robot's hump and whether these responses helped bring the hand back to the original target.
By measuring the latency or "delay" in the response, they were able to determine if the treatment was taking place in the brain or spinal cord.
"We found that these reactions occurred so quickly that the only place they could be generated was the spinal circuits themselves," said co-author Dr. Jeff Weiler, a postdoctoral researcher at Western University.
"What we're seeing is that these spinal circuits do not really care about what's happening at the joints, they care about where the hand is in the outside world and generate an answer that's trying to deliver the hand at its origin. "
This response generated by the spinal cord is called "stretching reflex" and has already been considered very limited in terms of movement aid.
"Historically, it was thought that these vertebral reflexes were simply acting to restore muscle length to what had happened before stretching," Dr. Pruszynski said.
"We show that they can actually do something much more complicated: control the hand in the space."
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Jeffrey Weiler et al. The stretching reflexes in the spine promote effective manual control. Nature Neuroscience, published online February 11, 2019; doi: 10.1038 / s41593-019-0336-0
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