A good night’s sleep may be more important for long-term brain health than we thought. Previous research has shown that disordered sleep—caused by insomnia and sleep apnea, among other things—interferes with cognitive function and may even increase the risk of developing Alzheimer’s disease. And we know that restorative sleep is critical for long-term memory. A new study from scientists at University of California, Berkeley, reveals that beta-amyloid protein in the brain may interfere with sleep quality and long-term memory formation, creating a vicious cycle.
For the study, the researchers recruited 26 healthy older adults with no signs of dementia and measured their brain amyloid levels using a PET scan. The volunteers were asked to study a list of word pairs before going to sleep. Overnight, the researchers measured their brain wave activity to gauge how deeply they slept. The next morning, the volunteers were asked to recall the word pairs as their brain activity was measured by fMRI.
The results? Not only did the volunteers with the most beta-amyloid have the poorest sleep quality, they also performed worse on the word-pairs recall test. Based on the results, the researchers speculated that beta-amyloid impairs deep sleep, which in turn blocks the movement of memories from the hippocampus, where short-term memories are formed and stored, into long-term memory storage in the prefrontal cortex.
So which comes first: disordered sleep or beta-amyloid in the brain? This study doesn’t answer that but previous research suggests a feedback loop in which disordered sleep increases beta-amyloid levels and higher beta-amyloid levels lead to disordered sleep.
For example, a single night of sleep deprivation raised beta-amyloid levels in spinal fluid (likely reflecting brain beta-amyloid levels) in a 2014 clinical trial. A 2013 study in animals demonstrated that during deep restorative sleep, the brain is "cleaned" by a tide of spinal fluid that washes out toxic proteins, including beta-amyloid. On the other hand, a 2012 study from Dr. David Holtzman at Washington University showed that brain beta-amyloid plaque formation in mice coincides with disordered sleep and that clearance of those plaques restored normal sleep patterns.
What can we do to avoid disordered sleep and ensure we catch some quality zzzz's at night? First, make sleep a priority. Ensure you set aside enough time for a full night's rest. If you suspect you have insomnia or sleep apnea, talk to your physician about treatment options. Remember, we spend almost a third of our lives asleep; it's critical for our brains that we make it count.
Aaron Carman, PhD, was previously the Assistant Director of Aging and Alzheimer's Prevention at the Alzheimer's Drug Discovery Foundation. Dr. Carman received his doctorate in microbiology and molecular genetics from The University of Texas Health Science Center at Houston.
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