Dementia profoundly affects brain activity during sleep by disrupting the brain’s natural rhythms and impairing critical restorative processes. One of the key ways dementia, particularly Alzheimer’s disease, influences sleep is through the disturbance of the circadian rhythm, which is the internal biological clock that regulates the sleep-wake cycle. This disruption leads to fragmented sleep, reduced deep sleep, and abnormal patterns of brain activity during rest[1][6].
In healthy brains, sleep plays a vital role in clearing toxic proteins such as beta-amyloid through the glymphatic system, a waste clearance mechanism that is most active during deep sleep. Beta-amyloid accumulation is strongly linked to Alzheimer’s disease and other dementias. When dementia disrupts sleep, this cleaning process is impaired, allowing harmful proteins to build up, which further damages brain cells and accelerates cognitive decline[2]. This creates a vicious cycle where poor sleep worsens dementia pathology, and dementia worsens sleep quality.
Research shows that in dementia, the circadian rhythms within specific brain cells become scrambled. For example, studies in mice modeling Alzheimer’s disease reveal that the normal daily activity patterns of hundreds of genes, including many associated with Alzheimer’s risk, are altered. This gene dysregulation affects key brain functions and contributes to the progression of the disease[1][6]. The disruption of circadian rhythms also manifests as common symptoms in dementia patients such as difficulty falling asleep, frequent nighttime awakenings, increased daytime napping, and sundowning—a state of confusion and agitation in the late afternoon or evening[1].
On a neurological level, dementia-related sleep disturbances involve changes in brain wave patterns. Normally, slow-wave sleep (deep sleep) is crucial for memory consolidation and brain restoration. Dementia reduces the amount and quality of slow-wave sleep, leading to impaired memory and cognitive function. Additionally, sleep deprivation or fragmented sleep causes the brain to enter microstates where it partially slips into sleep-like activity even during wakefulness. These micro-rests may represent the brain’s attempt to compensate for lost sleep but also reflect impaired neural engagement and attention lapses[3].
Insomnia, a common problem in dementia, further exacerbates brain dysfunction. Chronic insomnia disrupts the prefrontal cortex, which governs executive functions such as decision-making and reasoning, and the amygdala, which regulates emotions. This disruption leads to heightened stress responses, mood disturbances, and cognitive decline. Insomnia also reduces cerebral blood flow and slows neural communication, impairing the brain’s ability to clear metabolic waste like beta-amyloid, thereby increasing dementia risk[2][4].
The combined effect of dementia on sleep is not only a symptom but also a driver of disease progression. Poor sleep quality increases biological and psychological stress, which accelerates neurodegeneration. Caregivers often report that sleep disturbances are among the earliest and most challenging symptoms to manage in dementia patients[1]. This highlights the importance of understanding and potentially targeting sleep and circadian rhythm disruptions as part of dementia treatment strategies.
In summary, dementia affects brain activity during sleep by disrupting circadian rhythms, impairing the glymphatic clearance of toxic proteins, reducing deep sleep, and causing abnormal brain wave patterns. These changes contribute to cognitive decline and disease progression, making sleep disturbances both a consequence and a catalyst of dementia pathology.
Sources:
[1] https://hopecenter.wustl.edu/alzheimers-disrupts-circadian-rhythms-of-plaque-clearing-brain-cells/
[2] https://lonestarneurology.net/others/sleep-disorders-and-the-brain-why-youre-tired-even-after-8-hours/
[3] https://www.psychiatrist.com/news/when-sleep-deprived-brains-slip-the-body-follows/
[4] https://www.nuvancehealth.org/health-tips-and-news/the-link-between-insomnia-and-dementia-what-poor-sleep-means-for-brain-health
[6] https://www.sciencedaily.com/releases/2025/11/251102205012.htm
