Lets start by the beginning. What biological processes control sleep? Scientists strongly agree that there are two main ones: the first is the homeostatic drive , that is, a demand from the body, which needs to place itself in an ideal state of well-being for its survival (such as hunger or thirst); the second is a circadian process , which prompts us to regulate our ‘internal schedules’ with those of the Earth itself.
But sleep is not a totally unstoppable urge. As human beings, we are able to challenge the urge to sleep in moments of attention. For this reason, why does the dream invade us more easily in boring situations, no matter how much we try to resist?
Thanks to previous research, there is a consensus among scientists that cognitive and emotional factors also influence sleep-wake behavior ; however, the precise circuit mechanisms underlying its effects on sleep control were unknown. Up to now.
Research published in the journal Nature Communications has concluded that a part of the brain that is associated with motivation and pleasure, the nucleus accumbens, can also produce sleep. A finding that may explain why we tend to fall asleep in the absence of motivating stimuli, that is, when we are bored.
The scientists used genetic and optical techniques to monitor the activities of neurons in the nucleus acumbens in mice. In addition, they measured the behaviors that were mediated by these neurons. As a result, the team discovered that neurons in the nucleus accumbens have an extremely strong ability to induce sleep ; so powerful that it does not differ from sleep caused by the circadian and homeostatic processes that we mentioned at the beginning of the article.
This type of ‘natural’ sleep is known as slow-wave sleep , as it is characterized by the slow, high-voltage tension of the brain waves.
The key is in the adenosine receptors
“The classic somnogen adenosine is a strong candidate for eliciting the sleep effect in the nucleus accumbens,” according to Yo Oishi, lead author of the study.
Scientists have long known that the adenosine molecule represents a state of relative energy deficiency and induces sleep through adenosine receptors. And a specific subtype of adenosine receptors, A2A receptors, are expressed in the nucleus accumbens.
Precisely, caffeine, the most consumed psychostimulant in the world, also produces its excitation effect in the nucleus accumbens, by blocking these A2A receptors.
Responsible for this discovery is an international team of scientists, from the International Institute of Sleep Medicine (WPI-IIIS) of the University of Tsukuba, in Japan, and the Department of Pharmacology of Fudan University in the School of Basic Medical Sciences , located in Shanghai, China.
Compounds that activate A2A receptors in the nucleus accumbens can open safe therapeutic pathways for the treatment of insomnia , one of the most common sleep problems, with an estimated prevalence of 10-15% in the general population and 30-60% in the adult population.
Article reference:
Me, Oishi. ‘Slow-wave sleep is controlled by a subset of nucleus accumbens core neurons in mice’. Nature Communications 8, Article number: 734 (2017). Doi: 10.1038 / s41467-017-00781-4
