Study finds brain only intervenes in walking when discoordination exceeds a certain threshold

Walking is an activity that is often taken for granted. Most people assume that they can multitask, walking and chewing gum, without much effort. That’s because each leg can move rhythmically, independently of the other, under the control of its side of the spinal cord.

However, the human brain’s ability to coordinate gait so that a walker’s legs are half a step apart, called an “antiphase relationship,” is not so simple when an obstacle or asymmetry occurs, such as a curve in the path. A better understanding of how a normal walking cadence is maintained could lead to improved rehabilitation techniques for patients who have suffered traumatic brain injury or other neurological problems.

In a study published in Biology of communicationsResearchers at Osaka University collected kinematic data from healthy patients walking on a treadmill that was occasionally disrupted by a sudden change in speed. This resulted in a momentary loss of the antiphase relationship, but it was quickly restored when the subjects reoriented their walking movements. The data from this experiment were analyzed using a mathematical model of two coupled oscillators—similar to two pendulums connected by a spring—as well as a Bayesian inference method.

This approach allowed the researchers to calculate the most likely function that represents how the brain applies its control to coordinate leg movements. To further simplify the problem, phase reduction theory was applied, which assumes that the perturbed system returns to a regular periodic solution, called a limit cycle.

“Using Bayesian inference allowed us to infer the control of leg coordination in a quantitative way,” says the study’s lead author, Takahiro Arai.

Surprisingly, the researchers found that relative phase is not actively controlled by the brain until the deviation from the correct antiphasic orientation exceeds a certain threshold. In other words, the brain does not actively intervene to coordinate the relative position of the legs until they are offset by a certain amount. The researchers suggest that not requiring constant application of control improves both energy efficiency and maneuverability.

“From our model, we see that the brain is neither too controlling, which would limit our ability to overcome obstacles and also consume a lot of brain power, nor too lax, which could lead to a fall when the legs become too disordered,” says lead author Shinya Aoi.

This research could prove important in helping to improve walking in older people or people who have suffered the neurological effects of stroke or Parkinson’s disease. It could also lead to the development of physical aids that would help people walk more naturally.