Nerve cells in the brain can stop all movement in the body – even breathing

When a hunting dog picks up the scent of a deer, it sometimes freezes. On-site. The same can happen to people who need to concentrate on a challenging task.

Now researchers have made a discovery that increases our knowledge of what happens in the brain when we suddenly stop moving. Their study is published in Nature’s neuroscience.

“We have found a group of nerve cells in the midbrain that, when stimulated, stop all movement. Not just walking, all kinds of motor activity. They even make the mice stop breathing or breathe more slowly, and the heart rate slows down, ” explains Professor Ole Kiehn, co-author of the study.

“There are different ways to stop movement. What’s so special about these nerve cells is that once they’re activated, they cause the movement to be paused or frozen. Like pausing a movie. The actor’s movement suddenly stops on the spot.” says Ole Kiehn.

When the researchers stopped activating the nerve cells, the mice would start the movement exactly where it stopped. Just like when you press “play” again.

“This ‘pause-and-play’ pattern is very unique; it’s unlike anything we’ve seen before. It’s unlike any other form of locomotion or motor stopping that we or other researchers have studied. The movement doesn’t necessarily start where it stopped, but might start again with a new pattern,’ says PhD Haizea Goñi-Erro, who is the first author of the study.

The nerve cells stimulated by the researchers are found in the midbrain in an area called the pedunculopontine nucleus (PPN), and they differ from other nerve cells there by expressing a specific molecular marker called Chx10. PPN is common to all vertebrates including humans. So although the study was conducted in mice, the researchers expect the phenomenon to also apply to humans.

Not related to fear

Some might suggest that the nerve cells are activated by fear. Most people are familiar with the phenomenon of “freezing” caused by extreme fear. But that is not the case.

“We have compared this type of motor arrest with motor arrest or freezing caused by fear, and they are not identical. We are very confident that the arrest of movement here is not related to fear. Instead, we believe it has something to do with attention or vigilance, which is seen in certain situations,’ says assistant professor Roberto Leiras, who is a co-author of the study.

The researchers believe that this is an expression of focused attention. However, they emphasize that the investigation has not revealed whether this is actually the case. This is something that requires more research to prove.

Can help understand Parkinson’s symptoms

The new study may help us understand some of the mechanisms behind Parkinson’s disease.

“Motor stoppage or slow movement is one of the cardinal symptoms of Parkinson’s disease. We speculate that these special nerve cells in the PPN are overactivated in Parkinson’s disease. This would inhibit movement. Therefore, the study, which has primarily focused on the fundamental mechanisms that control movements in the nervous system, can ultimately help us understand the cause of some of the motor symptoms of Parkinson’s disease,” concludes Ole Kiehn.

Among other things, the researchers used optogenetics to stimulate the nerve cells in the brain stem.

Simply put, optogenetics is a biological technique that involves genetically modifying specific brain cells to make them more sensitive to light. This means that the cells can be activated by a flash of light.

In the study, the researchers were able to stimulate the specific group of nerve cells in mice and thus determine the motor function of these cells.