Removing Brain Immune Cells Restored Two Hours of Sleep in Alzheimer's Mice

The evidence comes from mice, not people. Researchers at the University of Kentucky, led by Shannon Macauley, reported the work in Alzheimer's & Dementia, the journal of the Alzheimer's Association, in 2026. They used APP/PS1 mice, which are bred to develop amyloid plaques, and normal littermates. All animals were female, studied at 6 and 18 months of age. Groups were small: the paper lists 4 to 12 mice per genotype and age for the sleep recordings, and 4 to 8 per group for the drug experiment.

Amyloid plaques are clumps of protein that build up in the brain, often decades before thinking problems appear. Sleep problems also appear early in people. The link runs both ways. Poor sleep is tied to more amyloid, and amyloid is tied to poorer sleep. What has been unclear is how plaques disrupt sleep. Much human research comes from people who already have mild cognitive impairment or dementia, where plaques sit alongside tangles of another protein, called tau, and nerve cell loss. That makes it hard to isolate the effect of plaques alone.

The team recorded the mice's brain activity and muscle activity to score sleep stages. They found that aging and plaques affected sleep in different ways. Plaques selectively reduced non-REM sleep, the stage that includes deep sleep. Aging mainly reduced REM sleep, and it also eliminated the usual rebound after sleep deprivation.

One result stood out. The loss of non-REM sleep appeared when plaques first formed, but it did not get worse as the plaque burden grew. According to the authors, this points to the arrival of plaques, not their amount, as the key trigger. They also found no obvious loss of neurons when the sleep loss began in 6-month-old mice. They argue this speaks against a mainly nerve-cell explanation.

Plaque-bearing mice showed signs of overexcited brain activity and poorly coordinated brain networks. Using whole-brain imaging, the team also found that microglia, the brain's resident immune cells, had multiplied. The increase was not limited to areas with plaques. It extended into thalamus regions and white matter tracts linked to sleep and waking.

To test cause, the researchers gave 6-month-old APP/PS1 mice the drug pexidartinib, which blocks a signal microglia need to survive, in their food for 14 days. This cleared about 87% of microglia. Sleep rose by more than two hours a day, and amyloid burden did not change. The authors conclude that microglia are a causal and reversible driver of plaque-linked sleep loss in this model. A separate group of four mice was also followed after the drug was stopped, to see what happened as microglia regrew.

Why does this matter for people? If a similar process occurs in humans, sleep trouble in midlife or later could be an early, measurable signal of brain changes, not just a side effect of worry or age. The authors suggest sleep and EEG measures, which record brain electrical activity, could serve as early markers of the disease. They also suggest they could be used as trial endpoints beyond memory tests.

There are limits. This was one mouse model, in females only, with small groups. Mice are not people, and plaque-driven sleep loss in mice may not match the human picture. Wiping out most microglia is also not a practical treatment, since these cells do important work in the brain. The study shows microglia are involved. It does not show that dampening them would help people sleep or slow dementia. The weakest point of the argument is the leap from mice to people.

The press coverage went somewhat further in tone. ScienceDaily, summarizing a University of Kentucky release, quoted Macauley calling the results "mind-blowing and unexpected" and "paradigm-shifting." She said the microglia act "as if the microglia are partying all night, and keeping the brain awake." Those are her characterizations of the work, not findings reported in the paper.

The study's own conclusion is more measured: microglia are a promising target for restoring sleep before symptoms begin. What to watch next is whether gentler ways of calming microglia, rather than removing them, can bring back sleep in animals, and whether that approach ever gets tested in people.

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