Key takeaways:

• A study reveals that skin temperature signals are processed in the brain to influence REM sleep and cataplexy in narcolepsy.
• Researchers found that a drop in skin temperature increases the likelihood of cataplexy, while warming the skin enhances REM sleep and suppresses cataplexy.
• The findings identify specific nerve cells (MCH neurons) in the hypothalamus that react to skin temperature to control these brain states.
• The discovery opens possibilities for non-medicinal, everyday approaches to managing narcolepsy symptoms.

Temperature signals from the skin are processed in the brain, influencing REM sleep and sleep-related disorders such as narcolepsy, according to researchers at the University of Bern and Inselspital, Bern University Hospital.

The study, published in Science Translational Medicine, provides evidence that skin temperature plays a central role in controlling brain states. In collaboration with the University of Lyon, the team demonstrated that the brain possesses neuronal systems that respond to skin temperature. In narcolepsy, these systems act as a switch, determining whether the brain enters REM sleep or triggers muscle paralysis (cataplexy) while the person is awake.

To investigate the effects of skin temperature on brain states, researchers conducted both animal and human studies. They found that a drop in skin temperature increases the likelihood of cataplexy in both people with narcolepsy and narcoleptic mice. Conversely, manipulating skin temperature to be warmer had a different effect. In mice, they also demonstrated that manipulating skin temperature has a direct impact on the expression of cataplexy and REM sleep.

“We assumed that warming the skin would increase both REM sleep and cataplexy, given that muscle paralysis occurs in both cases,” says Antoine Adamantidis, PhD, co-author of the study, professor of neurophysiology, and director of the Experimental Neurology Center at Inselspital, Bern University Hospital, in a release. However, the study showed that increasing skin temperature enhances REM sleep while it suppresses cataplexy. He adds: “The fact that skin temperature controls these two similar muscle states in opposite ways came as a surprise.”

The researchers identified special nerve cells, known as MCH (melanin-concentrating hormone) neurons, in the hypothalamus that react to skin temperature and help control whether the brain switches to a state of REM sleep or cataplexy.

“It is well known that the body influences the brain. But it is astonishing that even slight changes in skin temperature can trigger either REM sleep or cataplexy,” says Markus Schmidt, MD, PhD, last author of the study, head of sleep medicine at the Sleep-Wake-Epilepsy Center at Inselspital, Bern University Hospital, and research group leader at the Department for BioMedical Research at the University of Bern, in a release.

The findings are relevant for improving the long-term treatment of people with narcolepsy.

“Our findings demonstrate the close communication between the brain and body and open up new possibilities for reducing symptoms such as cataplexy using non-medicinal, everyday approaches,” says Claudio Bassetti, MD, co-author of the study, professor of neurology, dean of the Faculty of Medicine at the University of Bern, and director of teaching and research at Insel Gruppe AG, in a release.

The researchers now intend to examine whether and how targeted changes in skin temperature can promote REM sleep and reduce cataplexy attacks in patients with narcolepsy.

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