For a famous cartoon character like "Homer Simpson," narcolepsy can lead to all sorts of silly situations that make us laugh when we watch him.
But in real life, suddenly falling asleep while driving, working, or even in the middle of a conversation is not funny at all. Researchers in Japan have now discovered that a group of neurons in the brain paralyze and anesthetize the body during sleep. They found that problems with these neurons can lead to conditions including narcolepsy, cataplexy, and REM sleep behavior disorder. The research team from Tsukuba University states that REM sleep is directly associated with dreaming. When people are in this deep stage of sleep, their eyes continue to move, but their bodies remain still. Researchers refer to this partial paralysis of the body muscles during REM sleep as REM atonia. For patients with REM sleep behavior disorder, their bodies do not experience this paralyzed effect during sleep. In fact, people suffering from this disorder continue to move, often shouting or punching, and can jump or stand during their sleep.
In a study conducted using laboratory mice, Professor Takeshi Sakurai and his team examined the brain regions that prevent different types of movement during REM sleep. Their research revealed that the ventromedial medulla of the brain plays a key role in paralyzing people's movements during sleep, as this brain area receives signals from the subcoeruleus nucleus, which anesthetizes movement functions while falling asleep. Professor Sakurai clarified: "The anatomy of the neurons we found matches what we already know, but it confirmed that it was linked to neurons that control voluntary movements, not those that control involuntary muscles such as the eye muscles or internal organs. Most importantly, they were inhibitory, meaning they can prevent muscle movement even when active."
Finding a Link to REM Sleep Behavior Disorder: When the study authors blocked input signals to the ventromedial medulla in mice, they noticed that the mice began to move during sleep, similar to what happens in patients with REM sleep behavior disorder. In contrast, narcolepsy causes patients to unexpectedly fall asleep at any time of the day. Cataplexy, a similar condition that leads to people suddenly collapsing after losing control of their muscles, is characterized by paralyzed bodies that behave as if they are in REM sleep, even though these patients are not fully asleep.
Additionally, Sakurai's team tested the theory that these disorders are connected to the same neurons that affect REM sleep in the brain. They studied the brains of mice experiencing cataplexy episodes after consuming chocolate, again revealing a connection between the brain circuits that control REM sleep and cataplexy. The authors of the study also add that future tests will need to examine how emotions, which can also trigger cataplexy, affect these neurons.
