You are walking briskly, and suddenly, someone calls out to you. You stop in your tracks and turn all your attention to the person who has hailed you.
This arrest of action happens naturally in us. However, science is yet to completely understand the brain circuits involved in bringing a moving body to a halt. A serendipitous find by researchers from the University of Copenhagen, Denmark, may have cracked the code.
In their study published in Nature Neuroscience, the researchers identified certain neurons that trigger the ‘stop’ signal. They found that these neurons are spread across the midbrain in a region called PPN (pedunculopontine nucleus). Also, the same neurons in another part of the PPN take up the opposing activity and initiate movement.
The front-end neurons arrest the movement, whereas those at the back end initiate action. This research could help understand movement disorders better.
Hitting the pause button
Ole Kiehn, professor of integrative neuroscience at the University of Copenhagen, Denmark, tells Happiest Health that movement is not a continuous flow. It is episodic, with periods of movement followed by periods of arrest. “And the research team has made significant progress in comprehending the mechanisms behind the movement arrest,” he says.
Experimenting on mice, the researchers first genetically modified the neurons called Chx10 neurons to make them sensitive to light. Then they used light to stimulate the neurons.
When they activated the neurons with a flash of light, the mice stopped moving altogether. “We saw that when activated, [the neurons] halted ongoing activities such as walking, grooming, and even [slowed] breathing in the mice,” says Prof Kiehn.
He adds that not only body movements paused but also involuntary activities such as breathing and heart rate.
Play and resume
Why is this stopping activity particularly unique? When the researchers removed the light stimulus, the mice resumed their movement exactly from where they had left off — akin to pressing the play button on a video.
“This pause-and-play pattern has never been described before,” Prof Kiehn says.
However, the researchers clarify that these neurons are not involved in another kind of freezing of motion, which is often seen in people’s response to fear. Instead, they are active only in situations that require attention that preempts a pause.
The researchers state in the paper that a temporary pause could increase attention as the neurons also send signals to other parts of the brain that are involved in cognition.
These results throw light on movement difficulties characteristic of late-stage Parkinson’s disease. The researchers speculate that these Chx10 neurons could be overactive in the condition, and they plan on investigating this further.
