Surely on more than one occasion, in order to better listen to a conversation, you have stopped dead trying to capture every word of what someone in the distance is trying to communicate to us, as if that ‘frozen state’ activated your hearing better. Now, researchers at the University of Copenhagen have made a discovery that adds to our understanding of what happens in the brain when we suddenly stop moving, not out of fear but because of the need to focus on a challenging task. Like when a hunting dog detects the scent of a deer, which sometimes freezes. The same can happen to people who need to focus on a challenging task.
Professor Ole Kiehn, co-author of the study, explains in a statement: “We have found a group of nerve cells in the midbrain that, when stimulated, stop all movement. Not just walking; all forms of motor activity. They even make the mice stop breathing or breathe more slowly, and the heart rate slows down,” adding, “There are several ways to stop movement. What is so special about these nerve cells is that, once activated, they cause movement to stop or freeze. It’s like putting a movie on pause. The movement of the actors stops suddenly on the spot.
When the researchers finished activating the nerve cells, the mice started the movement exactly where it stopped. Same as when you press “play” again.For her part, Dr. HaizeaGoñi-Erro, a signatory to the study, declares: “This ‘pause and play pattern’ is very unique; It’s unlike anything we’ve seen before. It is unlike other forms of motor movement or arrest that we or other researchers have studied. There, the movement does not necessarily start where it stopped, but can start again with a new pattern.
Different from fear
The nerve cells stimulated by the researchers are found in the midbrain in an area called the pedunculopontine nucleus (PPN), and differ from other nerve cells there by expressing a specific molecular marker called Chx10. PPN is common to all vertebrates, including humans. Although the study was conducted in mice, the researchers hope the phenomenon will apply to humans as well.
Some might suggest that 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 engine stall to engine stall or fear freezing, and they are not identical. We are very confident that the stopping of movement observed here is not related to fear. Instead, we think it has something to do with attention or alertness, which is seen in certain situations,” says assistant professor Roberto Leiras, co-author of the study.
Understanding Parkinson’s
The new study may help us understand some of the mechanisms of Parkinson’s disease. «Motor arrest or slow movement is one of the cardinal symptoms of Parkinson’s disease. We speculate that these special nerve cells in NPP are overactivated in Parkinson’s disease. That would inhibit movement. Therefore, the study, which has mainly focused on the fundamental mechanisms that control movement in the nervous system, may help us understand the cause of some of the motor symptoms in Parkinson’s disease,” concludes Ole Kiehn.
