Disrupting REM sleep halts memory consolidation
A new study suggests that disrupting brain activity in sleeping mice, specifically during the rapid eye movement (REM) phase, can stop the animals remembering things they learned that day.
The research, reported in the journal Science, is the clearest evidence to date that REM sleep is critical for memory.
By switching off certain brain cells, the researchers silenced a particular, rhythmic type of brain function – without waking the mice. If they did this during REM sleep, the mice failed subsequent memory tests.
REM sleep is the phase during which, at least in humans, dreams take place. It is a mystery what our brain does during REM sleep, while our eyes flicker and our muscles relax. Simply waking up humans or animals when they enter the REM phase, for example, causes stress and other problems that can confound any memory tests.
Dr. Sylvain Williams, from McGill University in Canada, working with colleagues at the University of Bern, Switzerland, used a technique to solely disrupt REM sleep activity in mice.
Using the system known as “optogenetics”, he and his colleagues were able to control a particular population of brain cells in the mice, just by shining light through a tiny, implanted optical fiber. Whenever they switched on the light, they drastically reduced a particular rhythm in the brain, called “theta oscillations”. And if that disruption was delivered during a mouse’s REM sleep, there were consequences.
They found that when they disrupt activity only during REM sleep, and not other sleep, they basically eliminate consolidation and memory formation.
So it seems that REM sleep is crucial, in some cases, for laying down new memories. Williams said this arguably poses more questions than it answers.
Recent studies have tended to focus on deep, non-REM sleep instead, during which brain cells fire in various patterns that reflect memory consolidation and “re-play” of the day’s experiences. Williams said that for the moment, they still don’t know the difference between these two phases of sleep.
Williams suggests that it is an eye-opener to say that REM sleep has a very central role in these processes. Whatever that role is, the new findings suggest it involves the oscillations that the scientists disrupted – in which brain cells synchronise their activity, leading to a widespread and measurable rhythm with, in this case, about seven beats per second.That signature could be something to study in patients with dementia or other memory problems, Williams said.
Source: BBC
