Dreaming. REM sleep is understood to be a critical component of sleep in all mammals, including humans. Credit: © Anton Maltsev / Fotolia
For decades, scientists have fiercely debated whether rapid eye movement (REM) sleep – the phase where dreams appear – is directly involved in memory formation. Now researchers provide evidence that REM sleep does, indeed, play this role – at least in mice. “We already knew that newly acquired information is stored into different types of memories, spatial or emotional, before being consolidated or integrated,” says Sylvain Williams, a researcher and professor of psychiatry at McGill.
“How the brain performs this process has remained unclear – until now. We were able to prove for the first time that REM sleep is indeed critical for normal spatial memory formation in mice,” explains Williams. In this new study, they used optogenetics, that enables scientists to target precisely a population of neurons and control its activity by light. “We chose to target neurons that regulate the activity of the hippocampus, a structure that is critical for memory formation during wakefulness and is known as the ‘GPS system’ of the brain,” Williams says.
Sleep stages
To test the long-term spatial memory of mice, the scientists trained the rodents to spot a new object placed in a controlled environment where 2 objects of similar shape and volume stand. Spontaneously, mice spend more time exploring a novel object than a familiar one, showing their use of learning and recall. When these mice were in REM sleep, however, the researchers used light pulses to turn off their memory-associated neurons to determine if it affects their memory consolidation. The next day, the same rodents did not succeed the spatial memory task learned on the previous day. Compared to the control group, their memory seemed erased, or at least impaired.
“Silencing the same neurons for similar durations outside REM episodes had no effect on memory. This indicates that neuronal activity specifically during REM sleep is required for normal memory consolidation,” says Boyce, a PhD student. REM sleep is understood to be a critical component of sleep in all mammals, including humans. Poor sleep-quality is increasingly associated with the onset of various brain disorders such as Alzheimer’s and Parkinson’s disease. In particular, REM sleep is often significantly perturbed in Alzheimer’s diseases (AD).
http://www.mcgill.ca/newsroom/channels/news/rapid-eye-movement-sleep-keystone-memory-formation-260845
http://science.sciencemag.org/content/352/6287/812
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