New evidence may have identified where in the brain REM sleep originates and how to generate it by technology using light. Using optogenetics, neuroscientists have been able to stimulate neurons involved in REM sleep, and induce REM sleep using it.
Over time, the function and nature of sleep has has slowly been unveiled and its role in a number of conditions has been elucidated. REM sleep is unique because it is distinguished by the random movement of the eyes, muscular inactivity and the ability to dream. The role of sleep may have been shown to be important in a number of degenerative conditions and general health. The function of sleep varies widely from the consolidation of memories to the removal of by-products from the brain. REM sleep specifically consolidates memory related to learning actions like riding a bike, termed procedural memory.
A new study by Weber and colleagues has focused on an area of the brain responsible for the origin of REM sleep. It was known previously that the brainstem and pons may be important in sleep generation and this study highlighted the ventral medulla in sleep generation. The team demonstrated a GABA pathway strongly influences the production of REM sleep in mice. The team showed this by using an optogenetic (the use of light to control cells) switch to stimulate the ventral medulla GABAergic neurons. This not only induced REM sleep in the sleeping mice within seconds, it also prolonged it. Taking away the stimulation of these neurons had the opposite effect. The team observed recordings and found that the ventral medulla neurons were more active during REM sleep. The technique also showed these neurons to be active during eating and grooming. There is strong evidence to show that activation of GABA neurons in the ventral medulla was necessary for the development of REM sleep and its maintenance. The team believed that the effect may have been in part sustained by the inhibition of REM suppressing GABAergic neurons in the ventrolateral periaqueductal grey.
“People used to think that this region of the medulla was only involved in the paralysis of skeletal muscles during sleep,” said lead author Yang Dan, a UC Berkeley professor of molecular and cell biology and a Howard Hughes medical institute investigator. “What we showed is that these neurons triggered all aspects of REM sleep including muscle paralysis and the typical cortical activation that makes the brain look more awake than in non-REM sleep.”
The relevance of REM sleep to other conditions has also been studied extensively. “Many conditions are correlated with changes in REM sleep and some widely used drugs affect REM sleep, so it seems to be a sensitive indicator of mental and emotional health,” said first author Franz Weber. “It is hoped that studying the sleep circuit might lead us to new insights into these conditions as well as neurological conditions that affect sleep, like Parkinson’s and Alzheimer’s.”
The team also discovered that activating these neurons during wakefulness led the mice to eat more. They observed that the GABAergic neurons were most active during awake periods when the mice were eating or grooming, activities that may be pleasurable to the animal. The team also demonstrated that stimulating those different regions of the medulla where glutamatergic neurons exist immediately awakened the mice, showing that opposing mechanisms in the brain exist and a complex interaction between different regions takes place during wakefulness and during sleep. “Other people have found that noradrenergic neurons, which are active when you are running, closed down when eating or grooming. So it seems like when you are relaxed and enjoying yourself, the noradrenergic neurons switch off and these GABAergic neurons in the medulla turn on,” Yang Dan commented.
The beneficial nature of the study is in finding an origin of REM sleep and this may generate further research into feasible treatment or remedies to sleep related concerns. The causal sequence in relation to conditions known to be associated with deficient sleep may be further illuminated in the future as a consequence, and this may be productive news for those individuals aiming to overcome sleep related conditions.
What are further benefits of a healthy night’s sleep?