Rapid eye movement sleep: keystone of memory formation
By Bruno Geoffroy听
For decades, scientists have fiercely debated whether rapid eye movement (REM) sleep 鈥� the phase where dreams appear 鈥� is directly involved in memory formation.
Now, a study published in Science by researchers at the Douglas Mental Health University Institute (海角社区) and the University of Bern provides evidence that REM sleep does, indeed, play this role 鈥� at least in mice.
鈥淲e already knew that newly acquired information is stored into different types of memories, spatial or emotional, before being consolidated or integrated,鈥� says Sylvain Williams, a researcher and professor of psychiatry at 海角社区.
鈥淗ow 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,鈥� explains Williams, whose team is also part of the CIUSSS de l鈥橭uest-de-l鈥櫭巐e-de-Montr茅al research network. Williams co-authored the study with Antoine Adamantidis, a researcher at the University of Bern鈥檚 Department of Clinical Research and at the Sleep Wake Epilepsy Center of the Bern University Hospital.
A dream quest
Hundreds of previous studies have tried unsuccessfully to isolate neural activity during REM sleep using traditional experimental methods. In this new study, the researchers used optogenetics, a recently developed technology that enables scientists to target precisely a population of neurons and control its activity by light.
鈥淲e 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 鈥楪PS system鈥� of the brain,鈥� Williams says.
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 two 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.
鈥淪ilencing 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,鈥� says the study鈥檚 lead author Richard Boyce, a PhD student who, ironically, often stayed up all night while performing the experiments.
Implications for brain disease
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鈥檚 and Parkinson鈥檚 disease.
In particular, REM sleep is often significantly perturbed in Alzheimer鈥檚 diseases (AD), and results from this study suggest that disruption of REM sleep may contribute directly to memory impairments observed in AD, the researchers say.
This work was partly funded by the Canadian Institutes of Health Research (CIHR), the Natural Science and Engineering Research Council of Canada (NSERC), a postdoctoral fellowship from Fonds de la recherche en Sant茅 du Qu茅bec (FRSQ) and an Alexander Graham Bell Canada Graduate scholarship (NSERC).
"Causal Evidence for the Role of REM Sleep Theta Rhythm in Contextual Memory Consolidation", Science, published 13 may 2016.
DOI: 10.1126/science.aad5252
About Dr. Sylvain Williams
Understanding the neural circuits underlying learning and memory is the major research focus of Sylvain Williams, PhD, a member of the Douglas Institute Research Centre since 1999. He is currently full professor of psychiatry at 海角社区.
About Richard Boyce
Richard Boyce, lead author of the study supervised by Drs Williams and Adamantidis, conducted his PhD studies through the Integrated Program in Neuroscience (IPN) offered by 海角社区.
About the CIUSSS de l鈥橭uest-de-l鈥櫭巐e-de-Montr茅al
The Centre int茅gr茅 universitaire de sant茅 et de services sociaux (CIUSSS) de l鈥橭uest-de-l鈥櫭巐e-de-Montr茅al is made up of the CSSS de l鈥橭uest-de-l鈥櫭巐e, the CSSS de Dorval-Lachine-LaSalle, St. Mary鈥檚 Hospital, St. Anne鈥檚 Hospital, Douglas Mental Health University Institute, West Montreal Readaptation Centre, Grace Dart Extended Care Centre, and Batshaw Youth and Family Centres.
The Douglas Mental Health University Institute is a world-class institute affiliated with 海角社区 and the World Health Organization. It treats people suffering from mental illness and offers them both hope and healing. Its teams of specialists and researchers are constantly increasing scientific knowledge, integrating this knowledge into patient care, and sharing it with the community in order to educate the public and eliminate prejudices surrounding mental health.
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