Walking over an icy surface while keeping your balance would seem to require a lot of thought, but we do it unconsciously -- and it's not our brains but our spinal cords that help keep us upright, researchers have found.
Scientist have discovered what they're calling a "mini-brain," a group of neurons in the spinal cord able to take in sensory information and instruct our muscles to make the tiny adjustments that help us keep our balance.
This mini-brain works by allowing the body to instinctively make subtle adjustments to foot positioning and maintain balance using light touch sensors in the feet, researchers at the Salk Institute in California report in the journal Cell.
"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," explains study senior author Martyn Goulding.
"Our study opens what was essentially a black box, as up until now we didn't know how these signals are encoded or processed in the spinal cord."
That encoding and processing fills the role of a control center for integrating motor commands from the brain with sensory information from the limbs, the researchers discovered.
The finding could open a path to new treatments for spinal cord injuries and conditions that hamper motor skills and balance, they say.
Our brains gather information from many sources to keep us upright and balanced; visual signals from our eyes can warn of a slippery surface, sensing mechanisms in our ears help keep our head level, while our legs and arms generate signals to keep everything in sync and our bodies in balance.
Using advanced imaging techniques on mice to track nerve fibers carrying signals from sensors located in the feet to the spinal cord, the researchers found those fibers connected with a cluster of neurons that are also connected with the motor area of the brain.
Mice in which those neurons were disabled through genetic modification proved much more clumsy navigating a narrow or slippery surface than normal mice, they discovered.
"We think these neurons are responsible for combining all of this information to tell the feet how to move," says postdoctoral researcher Steeve Bourane. "If you stand on a slippery surface for a long time, you'll notice your calf muscles get stiff, but you may not have noticed you were using them.
"Your body is on autopilot, constantly making subtle corrections while freeing you to attend to other higher-level tasks."
