Though sleep science is a relatively new field of study, the advances being made by researchers have been remarkable and fast-paced. It is the goal of sleep research to better understand sleep and be able to manipulate it in order to help those who suffer from sleep disorders and deficiencies. A team of scientists at MIT has brought that understanding one step closer with its latest study.
The group recently published a paper in the journal Proceedings of the National Academy of Sciences, in which they describe finding a way to create a period of REM sleep in laboratory animals. REM, or rapid eye movement, is the period of time during which we dream and process memories. It is integral to our health and ability to function properly both physically and mentally. Though every stage of sleep is essential and offers its own benefit, those who suffer from a lack or deficiency of REM sleep often face chronic health problems. According to Emery Brown, the Edward Hood Taplin Professor of Medical Engineering at MIT, the benefits of REM sleep only come during natural sleep. Sleep aids such as sedatives allow the body to rest, but can not induce this particular and necessary state. “What they do is create sedation,” he explains. “If you are lucky, the sedation allows your natural sleep mechanisms to take over.”
Though all sleep is good, and non-REM sleep is what allows us to feel rested and refreshed, without cycling back and forth between REM and non-REM sleep over the course of the night, our health and cognitive abilities suffer. This means that researchers need to find a way to help people cycle into REM sleep when they are unable to do so on their own. According to Brown, the way to accomplish that goal is to first understand each sleep stage separately.
Science has already established that there are specific neurons known as cholinergic cells that are in our brain and that are active while we are awake as well as when we are in REM sleep. According to Christa Van Dort, the paper’s lead author and a post doctorate researcher in the Department of Brain and Cognitive Sciences at MIT, “There was a lot of early evidence that cholinergic neurons were involved in this area, but nobody could actually say whether the firing of these specific cells was responsible for the transition to REM sleep.” To find out the answer to that question, the group undertook a study of the use of a technique known as optogenetics. Optogenetics utilizes a fiber optic device to shine bright light directly onto a specific group of cells in order to activate them.
The reason why the light acts to activate the cells is because the cells have previously been sensitized with a specific protein found in algae. Previous research has shown that particular light wavelengths enable the algae to move around. “In 2005, researchers at Stanford were able to put this algae protein into mammalian cells,” Van Dort explains. “They realized that if you put the protein into certain types of neurons you could then shine a light on them to activate them, and control the firing of the brain, at a single-cell level.”
Knowing this, Van Dort and her fellow researchers sensitized the cholinergic neurons in laboratory mice. “In this way we were able to push the mice into dream sleep,” she explains. The group discovered that when they activated the cholinergic neurons of the animals while they were in non-REM sleep, they were able to make a difference in the number of REM sleep cycles that the mice went through. In analyzing the sleep cycles that the mice experienced following the activation of the cells, they realized that it very closely resembled that of natural sleep.
This discovery is extremely significant to the study of the mechanism by which REM sleep happens, and the researchers are hopeful that it will aid in them being able to induce a natural REM sleep cycle in humans. Though there are several drugs on the market that are able to help people to lose consciousness and put them into a light sleep state, Van Dort says that they actually suppress REM sleep, as well as the deeper phases of a natural sleep cycle that are extremely important. “Figuring out how each of the components of sleep is controlled can help us design a way of reproducing natural sleep with different drugs in the future.”
In addition to the hope that activating cells in this way may be of help, Dr. Brown is also hopeful that being able to enhance people’s REM sleep cycles will also provide a benefit to help with cognitive improvement in the areas of learning and memory. The group is also hoping to come up with ways to improve better cycles of non-REM sleep. “The long-term goal is to really understand what controls each phase of non-REM and REM sleep, and then to selectively induce them both and reproduce the normal cycling of sleep stages.”
The results of the current research are particularly significant, as the question of whether cholinergic cells control REM sleep has long been unresolved. According to Robert McCarley, a professor of psychiatry at Harvard Medical School, having the ability to selectively activate the neurons has made all the difference. “This pioneering study used optogenetic control of activity of cholinergic neurons to provide evidence that REM induction occurs through activity of cholinergic neurons, those using the neurotransmitter acetylcholine. What is exciting about this study is the use of optogenetics to shed new light on a decades-long conundrum, and it heralds a new era in REM sleep neurophysiology using optogenetics