Researchers have made an intriguing discovery about what happens in the brain when movement suddenly stops. In a study published in Nature Neuroscience, they found a group of nerve cells in the midbrain that, when stimulated, induce a complete cessation of all motor activity, like pausing a film. These unique nerve cells, located in the pedunculopontine nucleus (PPN), not only stop walking but also impact breathing and heart rate. When the stimulation ends, movement resumes exactly where it left off, similar to pressing “play” again. While the study was conducted in mice, the researchers believe this phenomenon likely applies to humans due to the commonality of the PPN across vertebrates.
Not related to fear
Although some might associate the nerve cell activation with fear-induced freezing, the researchers found distinct differences. The motor arrest observed in this study is not linked to fear; instead, they propose it might be related to attention or alertness. Assistant Professor Roberto Leiras, a co-author of the study, emphasizes that the exact nature of this phenomenon requires further research to confirm their hypothesis about it being an expression of focused attention. While they believe this to be the case, more investigations are needed to fully understand the mechanisms at play.
May help understand Parkinson’s symptoms
The new study could offer valuable insights into Parkinson’s disease, particularly concerning its motor symptoms. Motor arrest and slow movement, common in Parkinson’s, might be related to the over-activation of the unique nerve cells in the brainstem’s PPN. By using optogenetics, a technique involving genetically modified brain cells sensitive to light, the researchers could stimulate these specific nerve cells in mice and understand their role in motor function. While more research is needed, this study provides a promising avenue for unraveling the mechanisms behind certain motor symptoms in Parkinson’s disease.