'Mini-brain' keeps us balanced
Walking on ice is made easier by a "mini-brain" in the spinal cord, scientists have discovered.
The cluster of spinal neurons integrates sensory information and unconsciously adjusts our muscles to maintain balance and avoid slipping.
US researchers identified the balance mechanism after mapping spinal cord circuits that process the sense of light touch.
A better understanding of the "mini-brain" could aid the development of treatments for spinal cord injury and diseases affecting motor skills and balance, say the scientists.
It could also lead to ways of preventing falls in the elderly.
Lead researcher Professor Martyn Goulding, from the Salk Institute in La Jolla, California, said: "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.
"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. Moreover, it was unclear how this touch information was merged with other sensory information to control movement and posture."
Working with mice, the scientists traced nerve fibres that carry signals from touch sensors in the feet to connections in the spinal cord.
There, the fibres connected with another group of nerve cells called ROR alpha neurons.
When the ROR alpha neurons were disabled, the mice were able to walk and stand normally on flat ground, but were hopeless at keeping their balance.
Made to walk across a narrow elevated beam, the animals struggled.
The neurons were at the centre of a "mini-brain" that integrates signals from the brain with sensory stimulation to make sure limbs move correctly, said the scientists, whose findings are reported in the journal Cell.
Co-author Dr Steve Bourane, another member of the Salk team, said: "We think these neurons are responsible for combining all of this information to tell the feet how to move.
"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."