A Bug Steps into a Hole…

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New study describes how the brain controls movement in walking stick insects. Credit: Trista Rada/Flickr

What happens when you accidentally step into a hole? You were expecting a solid landing, but all of a sudden, it’s not there. One leg is left hanging, and you are caught off-guard. How the body reacts in this situation says a lot about how the brain controls the muscles used to walk. A new study in the Journal of Neurophysiology from researchers at the University of Cologne in Germany used this idea on walking stick insects to understand how the brain times the activation of the leg muscles to contract when walking.

The brain controls and receives information about the body through an intricate network of cells called the nervous system. Walking reflects how the brain coordinates the muscles, and understanding this interaction can provide insight into how the nervous system works. The researchers study walking in insects because their nervous systems have fewer cells and are less complicated.

Taking a step can be divided into two phases: swing, when the foot is in the air, and stance, when it’s on the ground. Each phase requires the activation of different sets of muscles in the legs. When the foot touches the ground is the transitioning point between the two phases. The researchers wanted to know how the brain knows to activate the leg muscles used in stance. Does it wait for the leg to feel the pressure of the foot hitting the ground? Or does it do it automatically because it dictates the walking pace?

To answer this question, the researchers developed a new apparatus that instantaneously generates a hole beneath the insect’s foot as the insect moves across it. The researchers looked at five leg muscles used in stance and found that only the activation of one muscle, the flexor tibiae, a muscle in the thigh-equivalent in an insect, depended on the foot making contact with the ground. The other four muscles activated whether or not the foot touched the ground. However, the intensity of the activation of all five muscles, which corresponds to the strength of the muscle’s contraction, depended on how hard the foot hit the surface.

So next time you’re walking on uneven ground, know that you’ll be thinking twice.

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.

Reviewed by Matthias Gruhn, PhD

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