The Spinal Cord Is Smarter Than Was Thought

Often the brain is thought of as being the centre of complex motor control and function, as it turns out the spinal cord is smarter than we think. The circuits in this part of the nervous system that travel down the length of the spine control seemingly simple things like the pain reflex in humans. Recently University of Western Ontario has shown the spinal cord is able to process and control complex functions such as the positioning of the hand in external space, which requires sensory inputs from multiple joints that were previously thought to be processed and converted into motor commands by the cerebral cortex.

Subjects were asked to maintain hands in a target position then a three degree of freedom exoskeleton robot technology bumped their hands away from the target by simultaneously flexing or extending the wrist and elbow. Time taken for the muscles in the elbow and wrist to respond to being bumped and whether the responses helped to bring the hand back to the target were measured. Measuring the lag in responses enabled the team to determine whether the process was happening in the brain or spinal cord.

Jeff Weiler, PhD noted the responses happened so quickly the only place they could be generated from is the spinal circuits; what was seen is the spinal circuits don’t care about what is happening to individual joints, rather where the hand is in the external world and generate a response to put the hand back from where it came.

The stretch reflex is generated by the spinal cord and was previously thought to be limited in terms of how it helps movement, to act just to restore the length of the muscle to whatever happened before the stretch. With this work we are showing that spinal circuitry do something much more complicated like control the hand in space, adds Andrew Pruszynski, PhD.

Findings add to the understandings of neurocircuitry and neuroscience, and provides new information about targets to further rehabilitation science which may lead to new kinds of training regimens that focus on the spinal circuitry.