Researchers use optogenetics to trigger REM sleep in mice

Getting enough of the right kind of sleep is crucial for keeping both body and mind healthy. Now a team of researchers at MIT has moved a step closer to being able to produce natural sleep patterns. To develop better approaches to creating natural sleep, researchers need to study the extent to which the various sleep stages can be created first separately, and ultimately together.

Previous studies have indicated that neurons called cholinergic cells are active during both wakefulness and REM sleep, says the paper’s lead author, Christa Van Dort, a postdoc in Brown’s group 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,” she says.

To investigate whether cholinergic neurons could induce REM sleep, the team used a technique called optogenetics, in which a head-mounted fiber optic device is used to shine light onto a specific group of neurons.

The neurons are first sensitized to light using a protein found in algae. This protein responds to certain wavelengths of light, allowing the algae to move around, Van Dort says. “In 2005, researchers at Stanford [University] were able to put this algae protein into mammalian cells,” she says. “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.”

Van Dort and her colleagues applied the technique to a mouse known to express this algae protein in cholinergic neurons. “In this way we were able to push the mice into dream sleep,” Van Dort says.