Walking on a frozen road in the middle of winter requires intense concentration. One misstep and you can end up face down on the ground. Even though most of us have fallen at least once from slipping or otherwise losing our balance, we’ve had many more times when we recovered and stayed upright. How did we manage to maintain our position?
A team at the Salk Institute seeks to answer that question as they probe the neural map of the human body.
However, it is unclear how different sensations such as touch and pressure are utilized by the brain to maintain balance.
Sensory information from multiple organs such as sight from the eyes and sense of balance from ear canals are integrated to adjust our movements. The flood of information is overwhelming.
Scientists have proposed that the brain utilizes groups of neurons around the body to process these initial signals and pass on more integrated information to the brain.
The scientists utilized a modified rabies virus that they injected into the lumbar spinal cord of mice. The virus crosses synaptic gaps and travels through neurons, creating a map of the area.
The team of researchers found that neurons responsible for touch sensors on the feet, a critically important factor in balancing, are bunched together with another group of neurons called ROR-alpha. These neurons, named after the receptor found in their nucleus — RAR-related orphan receptor alpha — connect with other neurons from the motor region of the brain. Because they pass information from the sensors to the brain, ROR-alpha might serve an important purpose in balance as a place where signals from the feet and other organs are initially combined and processed before reaching the brain.
To discover the significance of ROR-alpha in balance, researchers genetically modified mice with disabled ROR-alpha neurons.
These modified mice show less sensitivity for movement on their skin and are less responsive to the tape that is stuck to their feet. However, the mice were still able to balance on flat ground. The mice were then subjected to a balancing task of walking across a narrow bridge, where they performed worse than the control group.
The result suggests that because of the reduced sensitivity in their feet, the mice were unable to notice their misstep in time for correction and thus slipped off the edge. Since balancing on a narrow walkway or on ice requires constant adjustments, decreased sensitivity may inhibit the ability to adjust, making the mice overcompensate or undercompensate.
Furthermore, the researchers found that ROR-alpha neurons have direct connections to the ventral spinal cord, which controls movement. Their place at the junction of the spinal cord and the brain allows them to combine signals from the brain and sensory neurons to ensure proper limb movements.
While ROR-alpha neurons may serve an important role in maintaining balance in a difficult task, such as balancing on a beam, the mechanism with which the body and brain process information is still unclear to scientists. However, the discovery of the role of ROR-alpha in balancing may lead to restoring balance in patients with spinal cord injury.