Sleep history predicts late-life Alzheimer's pathology
Findings suggest novel, sleep-based diagnosis and treatment methods
June 18, 2019
Science Daily/Society for Neuroscience
Sleep patterns can predict the accumulation of Alzheimer's pathology proteins later in life, according to a new study of older men and women published in JNeurosci. These findings could lead to new sleep-based early diagnosis and prevention measures in the treatment of Alzheimer's disease.
Alzheimer's disease is associated with disrupted sleep and the accumulation of tau and proteins in the brain, which can emerge long before characteristic memory impairments appear. Two types of hippocampal sleep waves, slow oscillations and sleep spindles, are synced in young individuals, but have been shown to become uncoordinated in old age.
Matthew Walker, Joseph Winer, and colleagues at the University of California, Berkeley found a decrease in slow oscillations/sleep spindle synchronization was associated with higher tau, while reduced slow-wave-activity amplitude was associated with higher ?-amyloid levels.
The researchers also found that a decrease in sleep quantity throughout aging, from the 50s through 70s, was associated with higher levels of ?-amyloid and tau later in life. This means that changes in brain activity during sleep and sleep quantity during these time frames could serve as a warning sign for Alzheimer's disease, allowing for early preventive care.
https://www.sciencedaily.com/releases/2019/06/190618102725.htm
Memories are strengthened via brainwaves produced during sleep
Researchers use medical imaging to map areas involved in recalling learned information while we slumber
May 15, 2019
Science Daily/Concordia University
Researchers have known about the close relationship between sleep and memory for decades. Now, a new study published in the journal NeuroImage looks at one important mechanism in that relationship. The research brings us closer to understanding how learned information turns into reliable memories during sleep.
The study was led by Thanh Dang-Vu, associate professor in the Department of Health, Kinesiology and Applied Physiology and Concordia University Research Chair in Sleep, Neuroimaging and Cognitive Health. In it, researchers studied how declarative information like facts and faces get stored after they have been learned. It has to do with brainwaves -- specifically, ones called sleep spindles, which are fast bursts of electrical activity produced by neurons mainly during Stage 2 sleep, prior to deep sleep.
Dang-Vu worked alongside Christophe Grova, associate professor in the Department of Physics, and researchers from the Cyclotron Research Centre at University of Liège in Belgium. Using medical imaging machines, they were able to assess brain activity related to these waves.
"It's hypothesized that sleep spindles play an important role in transferring information from the hippocampus to the neo-cortex," Dang-Vu says. "This has the effect of increasing the strength of memories."
To get the images they needed, Dang-Vu's team used both electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). They applied these tools to a group of student volunteers during and after a lab-based face-sequencing task. The students were shown a series of faces and asked to identify the order in which they were shown. The researchers scanned them while they were learning the faces, while they were asleep and again when they woke up and had to recall the sequences.
Sleep spindles reactivated
They then came back every day for a week and repeated the task without being scanned. After a week had elapsed, they had memorized the task, and were once again scanned during sleep and asked to recall the sequences.
"Our aim was to compare the sleep spindles from the night where the subjects learned the new information to the night where they didn't have any new information to learn but were exposed to the same stimulus with the same faces," Dang-Vu explains.
The researchers found that during spindles of the learning night, the regions of the brain that were instrumental in processing faces were reactivated. They also observed that the regions in the brain involved in memory -- especially the hippocampus -- were more active during spindles in the subjects who remembered the task better after sleep.
This reactivation during sleep spindles of the regions involved in learning and memory "falls in line with the theory that during sleep, you are strengthening memories by transferring information from the hippocampus to the regions of the cortex that are important for the consolidation of that specific type of information," he says.
Using non-invasive imaging to identify the mechanisms that strengthen memories can, he hopes, lead to improvements in our understanding of how memories work -- and can lead to improved interventions for people with sleep or memory issues.
https://www.sciencedaily.com/releases/2019/05/190515131750.htm
Cueing newly learned information in sleep improves memory, and here's how
March 8, 2018
Science Daily/Cell Press
Scientists have long known that sleep is important to the formation and retention of new memories. Memory consolidation is associated with sudden bursts of oscillatory brain activity, called sleep spindles, which can be visualized and measured on an electroencephalogram (EEG). Now researchers have found that sleep spindles also play a role in strengthening new memories when newly learned information is played back to a person during sleep.
The findings provide new insight into the process of memory consolidation during sleep. They may also suggest new ways to help people remember things better, according to the researchers.
"While it has been shown previously that targeted memory reactivation can boost memory consolidation during sleep, we now show that sleep spindles might represent the key underlying mechanism," says Bernhard Staresina of the University of Birmingham in the United Kingdom. "Thus, direct induction of sleep spindles -- for example, via transcranial electrical stimulation -- perhaps combined with targeted memory reactivation, may enable us to further improve memory performance while we sleep."
Sleep spindles are half-second to two-second bursts of brain activity, measured in the 10-16 Hertz range on an EEG. They occur during non-rapid eye movement sleep stages two and three. Earlier studies had shown that the number of spindles during the night could predict a person's memory the next day. Studies in animals also linked sleep spindles to the process by which the brain makes new connections. But many questions about the link between sleep spindles and reactivated memories during sleep remained.
Staresina along with Scott Cairney at the University of York, UK, suspected that experimental reactivation of memories might lead to a surge of sleep spindles in a sleeping person's brain. To find out, they devised an experiment in which people learned to associate particular adjectives with particular objects and scenes. Some study participants then took a 90-minute nap after their study session, whereas others stayed awake. While people napped, the researchers cued those associative memories and unfamiliar adjectives.
As expected, the researchers saw that memory cues led to an increase in sleep spindles. Interestingly, the EEG patterns during spindles enabled the researchers to discern what types of memories -- objects or scenes -- were being processed.
The findings add to evidence for an important information-processing role of sleep spindles in the service of memory consolidation, the researchers say.
"Our data suggest that spindles facilitate processing of relevant memory features during sleep and that this process boosts memory consolidation," Staresina says.
This new understanding of the way the brain normally processes and strengthens memories during sleep may help to explain how that process may go wrong in people with learning difficulties, according to the researchers. It might also lead to the development of effective interventions designed to boost memory for important information.
https://www.sciencedaily.com/releases/2018/03/180308120605.htm