US researchers have discovered a "mini brain" hidden in our spinal cord that helps us remain balanced while maneuvering our way through crowd or walking across an icy parking lot in winter so that we do not slip and fall.
Such a task happens unconsciously, thanks to a cluster of neurons in our spinal cord that integrate sensory information and make the necessary adjustments to our muscles.
"When we stand and walk, touch sensors on the soles of our feet detect subtle changes in pressure and movement. These sensors send signals to our spinal cord and then to the brain," explained Martyn Goulding, professor from the Salk Institute for Biological Studies, a California-based independent scientific research institute.
"The study opens what was essentially a black box, as of until now, we did not know how these signals are encoded or processed in the spinal cord," he added.
Every millisecond, multiple streams of information, including signals from the light touch transmission pathway that Goulding's team has identified, flow into the brain.
One way the brain handles this data is by preprocessing it in sensory way stations such as the eye or the spinal cord.
But until now, it has been exceedingly difficult to precisely identify the types of neurons involved and chart how they are wired together.
In their study, the Salk scientists demystified this fine-tuned, sensory-motor control system.
Using cutting-edge imaging techniques, they traced nerve fibres that carry signals from the touch sensors in the feet to their connections in the spinal cord.
They found that these sensory fibers wire together in the spinal cord with another group of neurons known as RORI neurons.
The RORI neurons, in turn, connect with neurons in the motor region of brain, suggesting they might serve as a critical link between the brain and the feet.
When Goulding's team disabled the RORI neurons in the spinal cord using genetically modified mice developed at Salk, they found that these mice were substantially less sensitive to movement.
When the researchers had the animals walk across a narrow, elevated beam - a task that required more effort and skill - the animals struggled.
"We think these neurons are responsible for combining all of this information to tell the feet how to move," added Steeve Bourane, postdoctoral researcher in Goulding's lab.
The work offers a robust view of neural pathways and processes that underlie the control of movement and how the body senses its environment, the team concluded.
The paper was published in the journal Cell.
