Over the last several decades, scientists have debated about whether rapid eye movement (REM) sleep is directly linked to the formation of memories. REM sleep is the phase of the cycle when dreams appear. It is also the restorative phase of sleep.
Researchers from the Douglas Mental Health University Institute and University of Bern published a new study in Science to address the evidence that REM sleep does in fact play a role in memory formation. Well, in mice, at least; however, this is still a good foundation for human study.
Sylvian Williams, one of the researchers and a psychiatry professor at McGill (Douglas Mental Health University Institute) states that scientists already know that new information is stored in emotional or spatial memories before it is integrated or consolidated. Williams explains that it has been unclear how the brain performs this process until now. They are now able to prove that REM sleep is critical for forming spatial memory in mice. This is the first time these two processes have been linked.
This team of researchers is also part of the CIUSS de l'Ouest-de-l'Île-de-Montréal research network.
The Dream Quest
There have been hundreds of studies in the past that have unsuccessfully tried to isolate neural activity during rapid eye movement sleep using traditional methods of experimentation. In this new study, however, the scientists used what is known as optogenetics. This is a new technology developed recently that enables scientists to target populations of neurons and use light to control its activity.
Williams states that the researchers chose to target the neurons that regulate hippocampus activity. This is an area of the brain that is critical for the formation of memories during waking hours. It is commonly referred to as the “GPS system” of the brain.
Of course, again, it is mice that were used in this study, so it will require further human study. In order to test the long-term memory of mice, however, the researchers trained them to find new objects in a controlled environment where there were two similarly shaped and sized objects. The mice were spontaneous in that they explored novel objects more than familiar ones, which demonstrates their use of recall and learning.
In REM sleep, the mice were exposed to light pulses to “turn off” those neurons associated with memory in order to find out if it affected their memory consolidation. On the following day, those same mice were not able to complete the spatial memory task that they were able to do easily on the previous day. Compared to the control group, these mice’s memory seemed to be impaired, or even erased.
The study’s lead author, Richard Boyce, who is a doctoral student and, ironically, stayed up all night to watch the experiment, stated that quieting those same neurons at different durations in other stages of sleep did not affect the memory. This, to the researchers, indicates the activity of memory consolidation is specific to REM sleep.
It is widely known that REM sleep is critical to quality sleep in all mammals, even humans, which is why this study is so important. Poor quality sleep is frequently linked to the higher risk and onset of brain disorders like Parkinson’s and Alzheimer’s disease, two of the most debilitating conditions of our time.
Particularly, REM sleep is significantly problematic in those with Alzheimer’s disease and dementia. The results from this study tell us that REM sleep disturbance may be a contributing factor to memory impairment that is often observed in patients with Alzheimer’s disease.
Author: Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.
© 2021 American Sleep Association.