Sleep is connected to brain health and Dr. Laura Lewis investigates how you can reduce your chances of Alzheimer’s disease by getting more of it.
Sleep is Important for Brain Function
We often hear how important diet and exercise are to our health. Every day we are bombarded with ads and articles about the newest diet or fitness regime and we pay attention with hopes that these will help us live a longer, healthier life. However, while diet and exercise are important there is a third factor in longevity that is often ignored.
A good night’s sleep is incredibly important for your health and well-being. The more we understand about sleep, the more we understand the functioning of the brain. A good night’s sleep is not just important for physical health, it is inextricably linked to brain health. We are learning more and more about the relationship between sleep health and brain health.
For example, we know that a deficit of uninterrupted sleep can significantly increase the risk of Alzheimer's disease in an individual. What we don’t know, or more specifically didn’t know, was why.
Why Sleep is Important for Brain Function
In order to understand “the why”, Dr. Laura Lewis (Ph.D.) at the University of Boston and her research team at the Lewis Lab set out to investigate the connection between sleep and Alzheimer’s disease. Dr. Lewis set up a study to measure the relationship between sleep and Alzheimers - and more precisely the stages of sleep and Alzheimers. Her study, published in the journal Science, started by getting participants to skip a night of sleep ahead of a night in the laboratory. The exhausted participants would show up at her lab and promptly fall asleep with their heads situated in a Functional Magnetic Resonance Imaging (fMRI) machine. The fMRI machine measures the flow of blood in the brain. What she needed to understand was how the flow of blood was related to the activity of the brain (measured by electrical activity). In order to measure this brain activity, the participants were fitted with an electroencephalogram (EEG) cap - connected with a big bundle of wires - and inserted into the MRI to sleep.
Normal humans cycle in and out of four stages of sleep each night. These stages, sometimes called phases, are classified by the amount of movement exhibited by the body and proceed sequentially through the night. The first phase is the first non-REM (NREM) phase (Stage 1) where the body transitions from awake to asleep and exhibits twitching movements. The next phase is the light sleep phase (Stage 2), where the body transitions from asleep with movement, to asleep but paralyzed. The third phase is the deep sleep phase (Stage 3) where the body transitions from paralyzed sleep with minimal brain activity to lots of brain activity. Finally, the fourth phase is the rapid eye movement (REM) sleep (Stage 4) - which is the stage of sleep where we have dreams.
Deep Sleep non-REM and the Alzheimer's Connection
Dr. Lewis’ team found that a very interesting phenomenon occurs during deep sleep, during the NREM phase directly preceding REM. The team observed that during this NREM phase, all of the neurons in the participant’s brains began to coordinate in sync - something that rarely happens during many other times in our lives. This coordination was an important clue.
Dr. Lewis’s team observed not only were the neurons turning on and off in a coordinated fashion, but they were all turning on all at the same time, and off all at the same time. When all of the neurons turned off at the same moment, that reduced the amount of oxygen required to power the neuron activity. Less oxygen required in the brain means that it needs to circulate a smaller volume of blood to provide the needed oxygen. The lower pressure in the brain from the reduced flow of blood allowed a second fluid, called cerebrospinal fluid, to flow in its place. This was all known, but the key was what happened next.
As the cerebrospinal fluid flowed out of the brain, it was found to be carrying away extra stuff in it. This extra stuff was found to be chemicals, byproducts, and most importantly, toxins knowns as beta amyloids - which accumulate in the brain. The accumulation of these beta amyloids has been linked to a wide variety of neurodegenerative diseases - Alzheimer’s disease among them. During the full period of your nightly sleep, this process occurs many times. The result is an effect almost like a wave washing in and out of the brain, carrying away excess chemicals, byproducts, and toxins with each cycle.
Another key finding was that deep sleep, and the lack of blood flow that accompanies the switching of the neurons, is the only way for this cycle to occur - and this only happens for several hours each night.
A nap does not allow enough time for this to happen and for the brain to reach this phase. Sorry to break it to you, but you need more than a nap.
In summary of her findings:
- You need to sleep to keep your brain healthy.
- During sleep, your brain clears out accumulated beta-amyloid.
- Deep sleep is where the washing process actually happens.
- Beta-amyloid toxins are linked to neurodegenerative diseases.
- Naps are not enough to initiate the washing process. Deep sleep is required.
Thanks to Dr. Lewis and her team, we can now say, “go get some sleep, make sure it’s long and uninterrupted”. Your brain will thank you!