Alzheimer’s disease is a neurological disorder that impairs brain functions like memory and reasoning, and there is currently no known cure. People with this disease start off with basic forgetfulness, and eventually become unable to complete normal day-to-day tasks as they gradually lose control of their mobility.
Scientists have found abnormal proteins that accumulate in and around brain cells are the primary cause of Alzheimer’s disease. They’ve also found this disease depends on genetics, aging, and lifestyle choices, like being active and eating healthy. But they don’t know how other disorders, like sleep disorders, could exacerbate it.
Scientists have hypothesized that brain activity during sleep could be connected to Alzheimer’s disease, since a lot of important memory-associated events occur while we sleep. So scientists want to understand if disrupted brain function during sleep could be linked to the development of Alzheimer’s disease.
Researchers from Washington University in St. Louis recently tested whether Alzheimer’s disease is related to electrical activity that happens in our brains while we sleep. Most people experience changes in their brain activity early in the night as their bodies relax into sleep. Each of these changes, called sleep oscillatory events, lasts for about 20-40 minutes. The researchers hypothesized that the interaction of brain circuits during sleep oscillatory events would be different in patients with early Alzheimer’s disease, and could thus be used to diagnose it.
To test their hypothesis, the scientists used a machine that measures electrical activity in the brain, called an electroencephalograph, or EEG. They selected 205 participants who had previously completed at least 3 nights of EEG readings, 1 night of a home sleep apnea test, and a clinical dementia test. Based on their dementia tests, most of the participants were cognitively unimpaired, some participants were very mildly cognitively impaired, and 1 participant was mildly cognitively impaired.
The researchers asked the participants to wear the EEG as a headband while they slept so it could measure their brain waves during their sleep oscillatory events. The 3 types of sleep oscillatory events they measured during the experiment were theta bursts, sleep spindles, and slow waves.
The researchers explained theta bursts occur when people are in light sleep, and they help us process information and make memories. Sleep spindles happen during non-rapid eye movement sleep, and they are involved in consolidating memories. Slow waves happen during deep sleep, when our heart and breathing rates slow down, and they also play a role in developing memories.
The team sorted each patient’s individual slow wave events by how often they occurred at the same time as sleep spindles and theta bursts. They classified sleep spindles and slow wave events that occurred within 1.5 seconds of each other as coupled events. They also classified theta bursts and slow wave events that occurred within half a second of each other as coupled events.
The researchers found cognitively impaired people had weaker electrical activity during their theta bursts, and a bigger difference in their brain’s electrical activity during theta bursts versus slow waves. They also found cognitively impaired people and people with other biomarkers for Alzheimer’s disease had fewer slow waves coupled with theta bursts or sleep spindles. The team interpreted their results to confirm that disruptions in brain circuits involved in memory function during sleep could be linked to Alzheimer’s disease.
The researchers concluded EEG patterns of sleep oscillatory events could be used as biomarkers for Alzheimer’s disease. They suggested researchers could detect early indications of neurodegenerative processes related to Alzheimer’s from patients’ brain waves during sleep, even before they developed cognitive symptoms. They also suggested their results could provide an accessible and cost-effective tool for monitoring brain health and early Alzheimer’s, which could allow for earlier reaction and improved patient treatment.