A survey carried out by the Centers for Disease Control and Prevention (CDC) revealed that 50 to 70 million adults in the United States have chronic sleep disorders.
They also found that over 35 percent of them do not get the minimum 7 hours that an adult needs for optimal health.
This prompted the CDC to deem sleep deprivation a "public health epidemic," urging researchers to come up with new sleep therapies and unlock the mystery of how our brain induces the restful state.
Until now, it was believed that our brain uses several regions to alternate between sleep and wakefulness.
For instance, a popular hypothesis maintains that the cerebral cortex — that is, the upper part of the brain that can be found right beneath the skull — "emits" sleep-inducing slow brain waves, whereas wakefulness is controlled by the lower, mammalian part of our brain.
New research has turned this hypothesis on its head. Scientists from the Department of BioMedical Research at the University of Bern and the Department of Neurology at Inselspital, Bern University Hospital — both in Switzerland — find neurons that control both sleep and wakefulness.
The team was led by senior author Prof. Antoine Adamantidis, of the Department of Neurology at Inselspital. Thomas Gent, a researcher in the same department, is the first author of the paper.
The findings, which may pave the way for new sleep therapies, were published in the journal Nature Neuroscience.
Thalamic neurons drive sleep-wake cycle
Prof. Adamantidis and team used optogenetics to selectively switch neurons on and off in mice's brains.
Optogenetics is a technique in which neurons are genetically modified to respond to light. In this case, the scientists modified neurons in the rodents' thalamus, or the brain area responsible for relaying sensory information to the cortex.
The thalamus is also involved in mood regulation and states of arousal, or consciousness.
In this study, the researchers used prolonged stimuli to activate these neurons, which woke up the rodents. However, using slow stimuli in a rhythmic way induced a deep, non-rapid eye movement (REM) sleep in the mice, as measured by an electroencephalogram.
REM and non-REM sleep are the two main sleep phases; the former is the stage during which we dream, while the latter is the deep, restorative sleep.
To the authors' knowledge, this was the first time that a study has revealed that a single brain area promotes both sleep and wakefulness.
"Interestingly," explains Gent, "we were also able to show that suppression of thalamic neuronal activity impaired the recovery from sleep loss, suggesting that these neurons are essential for a restful sleep after [an] extended period of being awake."
The study's senior author also weighs in on the clinical significance of the findings.
"We believe that uncovering the control mechanisms of thalamic neurons during sleep and wake will be key to finding new sleep therapies in an increasingly sleep-deprived society."
Prof. Antoine Adamantidis