With stress, the body, through an ancestral survival reflex, voluntarily disrupts the sleep cycle in order to remain vigilant in the face of danger. Result: it can cause insomnia.
-1606799971.jpg "How stress affects our sleep")
- Our brain shifts our sleep range when it feels stress, it’s a primary survival mechanism.
- In our society where stress is constant, this mechanism no longer exists.
- However, this is what causes insomnia and sleep disorders among others.
There are no short or heavy sleepers, there are simply more or less stressed people. Researchers from the University of Nagoya (Japan) have discovered what links the circadian rhythm with stress in mammals. In our brain, certain neurons become particularly active when our body detects stress, which shifts our rest periods and creates insomnia and sleep disorders. The results were published on November 6, 2020 in the journal Science Advances.
An ancestral survival reflex
The circadian rhythm corresponds to the time slot of a day followed by all living organisms, from the largest to the most microscopic. In us mammals, this internal clock is located in the neurons of the suprachiasmatic nucleus of the brain which regulates our sleep-wake cycle. However, in the event of a potentially dangerous situation, the circadian rhythm signal is cut off to keep us awake so that we can escape that danger even when it would normally be time to sleep. This ancestral mechanism was essential for our ancestors who were always on the alert, and it helped them to survive. On the other hand, in our modern societies, where stress has become omnipresent, this rule of survival can trigger insomnia and other sleep disorders.
“It is well known that the circadian clock and stress have an effect on sleep, but it was unclear which neural pathway is crucial for circadian regulation of sleep and wakefulness.”, says Daisuke Ono, professor at the Environmental Medicine Research Institute of Nagoya University.
In order to understand how stress can disrupt our sleep, the researchers conducted an experiment on mice. They focused on corticotropin-releasing factor (CRF) neurons, located in the paraventricular nucleus of the hypothalamus, which play a role in the stress response. They investigated how sleep and wakefulness in mice would be affected when CRF neurons are activated.
Control the sleep/wake cycle
The results indicate that activated CRF neurons keep the animals awake and cause them to move quickly, indicating that their arousal state is promoted. The researchers also observed that the CRF neurons remained active when the mice were awake, and that when neuron activity was inhibited, the animals’ wakefulness and locomotor activities were reduced.
Previous research had already shown that inhibitory neurons in the suprachiasmatic nucleus, called GABAergic neurons, play an important role in regulating the activity of CRF neurons. Thus, it stimulates neurons in the lateral hypothalamus, which conditions us to stay awake. According to the researchers’ findings, GABAergic neurons in the suprachiasmatic nucleus control corticotropin-releasing factor neurons, which ultimately regulates our sleep/wake cycle.
“We have identified this neural pathway in mice, which are nocturnal animals. Further studies are needed to elucidate how the nocturnal and diurnal difference is regulated in the brain. In today’s society, sleep disorders are a serious problem. We hope our discovery will contribute to the development of new therapies for insomnia and other sleep disorders caused by stress or a disturbed circadian rhythm.”, concludes Daisuke Ono.
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