Interrupted REM sleep hampers memory building

Rapid eye movement sleep, or REM sleep, where the brain keeps active in the state of sleep and makes a sleeper dream lasts some 90 to 120 minutes. The evidence that memories are stored in the brain during REM sleep has first been obtained.

By using optogenetics, the research team led by professor Sylvain Williams at McGill University of Canada has discovered that any interruption in REM sleep can hamper memory building and published the finding in the academic journal “Science Magazine” of May 13.

Optogenetics selectively turns on or off neurons. The research team put experimental mice onto steel-made floor, generated noise and switched on weak electric current to teach them phobic reactions. When the mice went into sleep and further into REM state, the team made use of optogenetics to turn off nerve functions known to be involved in memory building in mice’s brains.

It turned out mice without interruption during the REM state showed phobic reaction or shunned away from steel-made floor when exposed to noise. On the other hand, mice that were interrupted in REM sleep didn’t display phobic reaction at any noise and stepped on current-flowing floor without hesitation, showing that they have lost the memory.

“It had been assumed that REM sleep would affect memory building but there’s been no solid evidence,” Professor Williams said. "The result of the research is meaningful in that it has found REM sleep plays critical roles in building of memory.