NEW insights into the mechanisms behind the sleep–wake cycle have been revealed in a study from the University of Bern, Bern, Switzerland. In contrast to earlier beliefs, the researchers discovered that the process is controlled by a single control centre, a finding which could aid in the development of new therapies for sleep disturbances.
There is currently limited understanding of how brain circuits control the sleep–wake cycle. Electroencephalogram (EEG) tests have shown that rhythmic oscillations, known as ‘slow waves’, are generated by the brain during sleep; these waves have an important function in maintaining sleep and helping recovery after a day’s activity. It has been hypothesised that these slow waves are generated in the cerebral cortex, a region in the upper part of the brain. This is in contrast to wakefulness, believed to be caused by the activity of ‘wake centres’ in the lower part of the brain.
For their study, the team wanted to establish the role of neurons on sleep and wakefulness in a central hub of the brain called the thalamus; the thalamus is involved in vital functions of the brain, such as attention, sensory perception, cognition, and consciousness. To do so, they used light pulses to precisely control the activity of thalamic neurons in mice, a technique known as optogenetics.
This experiment revealed that a small subset of thalamic neurons controls both sleep, by generating slow waves, and wakefulness. When the neurons were activated with regular long-lasting stimuli the mice woke up, whereas when activated in a slow rhythmical way, the mice’s sleep became deeper and more restful.
“Essential for a Restful Sleep”
Lead author Dr Thomas Gent, University of Bern, commented: “Interestingly, 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.”
New Sleep Therapies
This new understanding of how sleep is controlled and regulated could provide the basis for new treatments for chronic sleep disturbances, which are becoming increasingly prevalent. Prof Antoine Adamantidis, University of Bern, added: “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.”
James Coker, Reporter