Loss of Neurons, Not Lack of Sleep, Makes Alzheimer’s Patients Drowsy Digest
Neuron losses in the brain promote daytime sleepiness in Alzheimer’s disease.
Scientists have long believed that poor nighttime sleep drives the daytime sleepiness often experienced by people with Alzheimer’s disease. However, findings from a recent study suggest that the loss of wake-promoting neurons in the brain promotes daytime sleepiness in people with Alzheimer’s disease.
During nighttime sleep, the brain activates the glymphatic system, a self-cleaning process that rids the brain of toxic products, including amyloid-beta and tau tangles. Poor sleep promotes the accumulation of these products, which in turn, promotes poor sleep, creating a vicious cycle that affects brain health. Amyloid-beta accumulation and tau tangle formation are the primary pathological hallmarks of Alzheimer’s disease.
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The investigators recruited 33 people with Alzheimer’s disease, 20 people with progressive supranuclear palsy (a rare neurological disorder that affects balance, movement, vision, speech and swallowing), and 32 healthy people to participate in the study. They assessed the participants' brain activity using electroencephalography and assessed their sleep quality using polysomnography. Upon the participants' deaths, the investigators examined the participants' brains for neuronal changes and the presence of amyloid-beta or tau.
They found that people with Alzheimer’s disease exhibited an increased desire to sleep and exhibited fewer wake-promoting neurons in their brains, promoting daytime sleepiness. Conversely, people with progressive supranuclear palsy had a decreased desire to sleep and exhibited fewer sleep-promoting neurons, robbing them of the ability to fall asleep and causing sleep deprivation. The dominant toxic protein in the participants' brains was tau.
These findings suggest that neuronal losses in the brains of people with neurodegenerative disorders contributes to sleep irregularities, and these losses are due to tau accumulation. Learn more about the role of sleep in neurodegenerative disorders in this clip featuring Dr. Matt Walker.