Sleep, memory, learning and Alzheimer's diseaseJune 24, 2018 0 Comments
[by Tamara Sellman RPSGT CCSH for Advanced Cardiovascular Sleep Disorders Center]
Access to memory is one of the most traumatic symptoms of Alzheimer’s disease. When loved ones forget the names and faces of people around them, it can be a profound experience not only for those forgotten, but for the person struggling to access these memories.
While research continues to wrestle with the disease processes that occur during Alzheimer’s, a few things are already known and understood. One of them relates to the link between sleep and memory.
Sleep quality and quantity affect everyone’s memory
One doesn’t have to have Alzheimer’s disease to struggle with memory. All of us have had moments when we cannot recall information, though it is at “the tip of our tongue.” Sometimes stress or illness can be held responsible for normal glitches in memory, but often, it’s problems with sleep that are at the root of the problem.
According to information at Harvard’s Healthy Sleep website, research suggests a connection between sleep and two different brain functions: learning and memory.
It makes sense that the two should be related; after all, learning requires memory.
In order to make memories, our brains are said to participate actively in three functions:
- Memory acquisition (through formal learning or brand-new experiences, which occur while you’re awake)
- Memory consolidation (which seems to take place only during sleep)
- Memory recall (or the future access of memories while you are awake)
Learning and memory
Learning (whether in a classroom or through first-hand experience) is how we gather new information to eventually story into memory.
Sleep is said to assist with learning in two ways:
- Good sleep sharpens the mind and makes it easy to learn new things. When one is sleep deprived, they suffer from attention problems which make it hard to learn efficiently.
- Sleep itself provides the brain with the opportunity to consolidate memory, which includes memory processes used in learning new things. Poor sleep denies the brain this important opportunity.
This memory consolidation is thought to occur during specific stages of sleep which are marked by specific kinds of brain activity associated with memory formation and processing.
You may have heard that college students who take a nap after a long study session (or go to bed and get a good night’s sleep) are more likely to retain what they have learned. Some researchers think that memories (included the processing of new information) are moved to more complex areas of the brain during sleep in a process known as “consolidation.” In these new, permanent regions, the brain can more efficiently store and make available what has already been learned.
The synthesis of what has been learned (and stored in memory) also benefits from good sleep. If you’ve ever heard the story of geniuses who awaken to “Aha!” or “Eureka!” moments, you are witnessing the result of good sleep and well-consolidated memory in a brain supporting their effort to seek solutions to complex problems.
Newer research even points to our ability to learn even as we sleep. From the National Sleep Foundation comes this anecdote: “To test this idea, scientists exposed people to a sound and a pleasant smell while they slept. After the subjects woke up in the morning, they started sniffing when they heard the sound (even though it wasn't followed by a smell). In other words, they had learned the association while they slept.”
Other research suggests that one of the reasons why children, and especially infants, sleep so much is because sleep is a key developmental process which exists to help them consolidate new learning, memories, and information.
After all, our youngest are continually learning things that, as adults, we take for granted. Sounds, tactile sensations, tastes, cause and effect, even the simple physical differences between males and females in their household. Throw in more abstract thinking and it’s easy to see that their brains are building and forming at an exhaustive pace.
They need more sleep because they’ve got a lot of neurological filing to do. For those with traumatic brain injuries, or stroke patients, or people with Alzheimer’s disease, it may not be filing as much as cleaning out the files.
When during sleep does memory consolidation take place?
Researchers Rasch and Born have asked the question: “Why does the consolidation of memory have to take place during sleep?” They describe sleep as a kind of passive protector of memory, as well as a time for the brain to, without interruption, newly encode information learned during waking periods.
Dr. William Klemm points out in his column, Memory Medic, in Psychology Today that it’s no longer a question of whether sleep helps with memory consolidation. It’s more a question of how it does this. Klemm suggests that:
- Sleep can shield new memories from disruption and interference, and
- Our memories are “filed” according to how much importance we assign them as well as our expectations for remembering them
Rapid-eye movement (REM) sleep (or “dream” sleep)
Some studies show that REM sleep is a key player in acquiring newly learned information, especially if it is shaped by emotion or is complex information.
In fact, REM is also been shown to be the stage where “selective memory” can take root; some memories with traumatic or negative content may be processed differently in REM based on the influence of emotional content.
Because it is thought that content preserved for memory consolidation during sleep may be reactivated during REM (or dream) sleep, this could explain why some people have recurring nightmares.
Stage 3 sleep (also known as delta sleep, N3 sleep, or slow-wave sleep)
Other studies have looked at connections between stage 3 sleep and memory consolidation. This is the stage in which we achieve our deepest, most restorative sleep.
Research is ongoing, but worthwhile, given other connections to Alzheimer’s and poor sleep which have already been established.
Stage 2 sleep spindles may be linked to memory reactivation
In sleep science, one of the unique waveforms emitted by the brain during sleep is known as a “sleep spindle.” These bursts of brain activity, each occurring rhythmically during stage 2 sleep at around every 3 to 6 seconds, have been found to be linked to memory reactivation.
What happens to memory when we don’t sleep enough?
Some things we already know:
- We struggle to remain focused, attentive, and vigilant. Our guard is down, we drift and feel scattered.
- Our brains don’t function as efficiently as they should, making it harder to process new information or to access memories (including those related to learned information).
- We may find it hard to understand or interpret critical information in the moment. A person who is sleep deprived, who is driving a car, may see an obstacle up ahead and have a slower response to it because they lack sound judgment to process the information before them. This means they may wait too long before putting on the brakes.
- Job performance and physical performance are also suboptimal. Our brain is slow, our body is not in synch, muscles are less responsive. Mistakes while on the job, even injuries and accidents, can result.
- Our mood can also be affected in a way that influences memory. It is harder to learn new things or process new information if we’re suffering from dips into negative emotion.
It’s hard to dispute these observations. Who doesn’t focus, learn and remember better when they’ve had a good night’s sleep?
“As these research findings show, we cannot underestimate the importance of a good night's sleep," Dr. Clifford Saper (Harvard Medical School) told the Sleep Foundation in a recent discussion. “Brain imaging and behavioral studies are illuminating the brain pathways that are blocked or contorted by sleep deprivation, and the risks this poses to learning, memory, and mental health."
But, if even healthy people can struggle with these problems after losing sleep, imagine what it’s like for someone with Alzheimer’s disease.
Connecting poor sleep and Alzheimer’s disease
While even healthy people can occasionally struggle to recall a memory after losing sleep, people with Alzheimer’s experience this disturbing problem frequently. Dr. Steven Barczi, a prominent geriatric sleep physician at the University of Wisconsin-Madison, describes how the aging brain can contribute to memory problems:
“Sleep is a biological rhythm – a circadian rhythm. It tries to maintain regularity and rhythm, including sleep and waking. But as we age, those internal clocks can become desynchronized – and this is important when we start to talk about individuals with health problems, like those with memory illness or dementia.”
Poor sleep in those with Alzheimer’s not only impairs memory access, formation, and consolidation, but it also alters their emotional state and reduces their physical and mental performance. This is because Alzheimer’s is a disease which causes abnormal brain processing and the death of brain cells.
The loss of brain function caused by Alzheimer’s (and even some of its leading treatments) leads to sleep disruption, which leads to more dysfunctional brain processing, in a terrible, repetitive cycle.
Last April, research supported these recommendations, which suggested “insufficient sleep or poor sleep may contribute to the development of Alzheimer’s disease,” finding that even one night of poor sleep in their study resulted in a significant increases in the toxins known as beta(β)-amyloids found in the brain that lead to this neurological disease.
Fortunately, the National Institutes of Health (NIH) recently made two new recommendations based on research presented at the 2018 NIH Alzheimer’s Research Summit which relate to sleep and circadian research, which suggested that current research:
1. Expand efforts to understand the mechanics linking sleep problems with Alzheimer’s disease, and
2. Identify and reduce risk factors, which include, among other things, poor sleep