International Business Department           Liu Bojia           August 7, 2023

  We may have had the experience that when we are suddenly terrorised, we may suddenly be unable to walk out of fear, as if immobilised. Scientists have revealed the underlying neural mechanisms behind this fear-related termination of whole-body movement, such as the fact that the neural circuits that regulate this behaviour are located in the lower part of the brainstem, and that the pathways that activate these neurons encompass key brain regions such as the amygdala.

  However, this is not sufficient to explain all movement termination phenomena. It's not just fear that causes movement termination; sudden fixation can occur when we are focused on a challenging task, as well as when we are reaching certain goals. And what are the brain processes that change an individual's behaviour in a split second?

  A recent study published in Nature Neuroscience provides key insights into this question. A team of researchers from the University of Copenhagen, Denmark, found in mice that a special class of neurons located in the pedunculopontine nucleus (PPN) region of the midbrain act as a "remote control" for whole-body activity, pressing the pause button on whole-body movements when stimulated, not only to When stimulated, they hit the pause button on all body movements, not only terminating movements including walking, but also causing the mice's respiratory rate to drop or even stop completely, and their heart rate to slow down instantly.

  Previous studies have observed that PPN induces global movement termination.PPN is mainly composed of glutamatergic, cholinergic and GABAergic neurons, and among these three neuronal subpopulations, glutamatergic neurons expressing vesicular glutamate transporter protein 2 (Vglut2) are the most abundant.

  In this study, the team used a combination of anatomical, physiological and behavioural tools to reveal that a group of glutamatergic neurons expressing the transcription factor Chx10 is closely related to movement termination.

  Once these neurons are activated, they pause or freeze the movement, just as pressing the pause button during a film momentarily stops the movement of the actors in the picture; when the researchers stopped activating these neurons, the mice resumed from the "frozen" state, just as if they had pressed the play button, and restarted the movement.

  In addition to pauses in whole-body movement, the study also observed that the mice also experienced brief pauses in breathing and bradycardia.

Another key finding was that the pattern of motor termination in the latest study was different from those that had been studied previously, because after ending the activation of the neurons, these mice would continue to move from where they had previously stopped; whereas in the previous pattern, the resumption of movement could begin in a completely new pattern.

  "We have compared this type of motor arrest with arrests caused by fear to determine that this behaviour is not related to fear. Instead, we believe its related to attention or alertness." Professor Roberto Leiras, co-corresponding author of the study, said. The researchers believe that this phenomenon is a sign of possible concentration, but also say that this study is not enough to confirm this mechanism, so more research is needed to prove it.

  Since PPN is common in all vertebrates, including humans, the team expects that this phenomenon can also be found in humans.

  In addition to helping us understand the mechanisms underlying the brain, this research has important potential implications for disease treatment.

  Motor stagnation or retardation is one of the main symptoms of Parkinson's disease, and PPN has been pointed out as a potential therapeutic target for improving the symptoms of Parkinson's disease. Recent studies have speculated that these particular nerve cells in the PPN are over-activated in Parkinson's disease, thereby inhibiting motor behaviour. Therefore, this latest research focusing on the basic mechanisms controlling movement in the nervous system will help to understand the mechanisms of movement disorders in Parkinson's disease and find therapeutic strategies.