How a healthy brain paralyses you while you sleep

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  • Sleep disorders can cause involuntary physical actions, which are potentially dangerous
  • Researchers used mice to see which part of the brain is responsible for causing certain sleep-related illnesses
  • They found that these disorders could be due to blockages between certain neurons

Seeing someone unable to stay awake during a lecture, or punch and scream out in their sleep, are often tell-tale signs of serious sleep disorders. 

A group of researchers at the University of Tsukuba in Japan have identified neurons in the brain that link three sleep-related illnesses, providing a starting point for developing treatments. 

Narcolepsy, cataplexy, and rapid eye movement sleep behaviour disorder

Narcolepsy is a condition that “affects the brain’s ability to control sleep-wake cycles”, meaning a person can fall asleep at any time, even while driving.

Cataplexy is a related condition and a symptom of narcolepsy. It involves the sudden loss of voluntary muscle movement and is often triggered when experiencing strong emotions such as anger, excitement or fear.

Rapid Eye Movement (REM) is a phase of sleep where our eyes move around while our bodies are in a semi-paralysed state (known as REM-atonia) and remain still. 

Contrarily, with rapid eye movement behaviour disorder is accompanied with potentially harmful bodily movements (like punches or jumping), and persons with this condition lack REM-atonia.

Professor Takeshi Sakurai led the team of researchers to find the neurons in the brain responsible for preventing the behaviour associated with this disorder. 

 Unpacking the anatomy of mice brains

The researchers conducted their study on mice and targeted neurons that could likely be responsible. The neurons are in the part of the brain called the ventral medial medulla that receive input from another part of the brain known as the SLD.

“The anatomy of the neurons we found matched what we know,” Professor Sakurai explained.

“They 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.”

Blocking off neural links could be the problem

The researchers found that when they blocked input to these neurons, the mice began to move in their sleep, as seen in persons with REM sleep behaviour disorder.

The team also suspected that these neurons were related to the other two disorders, narcolepsy and cataplexy.

With these conditions, although an affected person is awake, their body will act as though it is in the REM phase of sleep. “We found that silencing the SLD-to-ventral medial medulla reduced the number of cataplexic bouts,” says Professor Sakurai. 

The researchers went on to say that the neurons they identified “could be a good target for drug therapies for people with narcolepsy, cataplexy, or REM sleep behaviour disorder”.

Image credit: Pixabay

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