We laugh when we see Homer Simpson falling asleep while driving, while in church, and while even operating the nuclear reactor.
In reality though, narcolepsy, cataplexy, and rapid eye movement (REM) sleep behavior disorder are all serious sleep-related illnesses.
In a new study, researchers have found neurons in the brain that link all three disorders and could provide a target for treatments.
The research was conducted by a team at the University of Tsukuba.
REM sleep correlates with when we dream. Our eyes move back and forth, but our bodies remain still. This near-paralysis of muscles while dreaming is called REM-atonia, and is lacking in people with REM sleep behavior disorder.
Instead of being still during REM sleep, muscles move around, often going as far as to stand up and jump, yell, or punch.
In the study, the team set out to find the neurons in the brain that normally prevent this type of behavior during REM sleep.
Working with mice, the team identified a specific group of neurons.
These cells were located in an area of the brain called the ventral medial medulla and received input from another area called the sublaterodorsal tegmental nucleus, or SLD.
The neurons were connected to neurons that control voluntary movements, but not those that control muscles in the eyes or internal organs.
Importantly, they were inhibitory, meaning that they can prevent muscle movement when active.
When the researchers blocked the input to these neurons, the mice began moving during their sleep, just like someone with REM sleep behavior disorder.
Narcolepsy, as demonstrated by Homer Simpson, is characterized by suddenly falling asleep at any time during the day, even in mid-sentence (he was diagnosed with narcolepsy).
Cataplexy is a related illness in which people suddenly lose muscle tone and collapse. Although they are awake, their muscles act as if they are in REM sleep.
The team suspected that the special neurons they found were related to these two disorders.
They confirmed their hypothesis using a mouse model of narcolepsy in which cataplexic attacks could be triggered by chocolate.
Overall, the experiments showed these special circuits control muscle in both REM sleep and cataplexy.
The neurons the researchers have identified in the ventral medial medulla could be a good target for drug therapies for people with narcolepsy, cataplexy, or REM sleep behavior disorder.
One author of the study is Professor Takeshi Sakurai.
The study is published in the Journal of Neuroscience.
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