Around 20 years ago, researcher Clifford B. Saper, Chairman of the Department of Neurology at BIDMC, and his colleagues carried out a study on sleep and discovered a set of nerve cells that actually may be ‘the brain’s sleep’ switch. However, further research needed to be conducted in order to bring such conclusions.

Recently, a study published in Nature Communications today, Saper and his fellow scientists has proven the claims of the older study and demonstrated the mentioned set of brain cells in mice. The cells are located in the ventrolateral preoptic nucleus which is actually a region of the hypothalamus. The VLPO neurons are vital to normal and healthy sleep. The new research aims to describe what happens when the VLPO neurons are activated. The findings support the claim that these cells are crucial for regular sleep.

How Was the Study Conducted?

Saper’s team worked with lab mice, and artificially stimulated the VLPO neurons in mice’s brains. The neurons were activated in a few different ways. In one set of experiments, the researchers have used a laser light beam to make the neurons fire, this is a process called optogenetics. In another one, they selectively activated the VLPOs with a chemical. In both cases, stimulating these neurons drove sleep. Saper concluded that these cells are active during sleep and that damaging them causes insomnia.

An interesting fact is that another study conducted in 2017 reported the opposite and that activating the VLPO neurons woke up lab animals. Saper’s team explained that if the VLPO cells are stimulated very fast (more than one to four times per second), they won’t fire up, but actually start shutting off, leading not to sleep, but to a state of wakefulness.

Additionally, Saper’s study found that activating the VLPO neurons causes a slight decrease in body temperature. Researchers were already aware that warm temperatures activate VLPOs, and that body temperature drops during sleep. However, they have noticed that body temperature drops in the exact moment the VLPO neurons start firing. With continued activation, the body temperature in the mice fell as five or six degrees Celsius, and Saper concluded that these neurons might help us understand better the phenomena of animal hibernation – particularly their prolonged sleep and decline in body temperature. Further research aims to take a closer look between sleep and body temperature.


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