Barcelona study of 116 adults: slow-wave sleep flattens before Alzheimer's symptoms appear

A study of 116 adults at Hospital Clínic de Barcelona found that the shape of slow brain waves during deep sleep changes across the Alzheimer's disease continuum. The changes were present even in people without cognitive impairment who have abnormal amyloid biomarkers, news-medical.net reports. The work was published in Alzheimer's Research & Therapy, and the authors suggest the changes may serve as non-invasive markers of preclinical disease. news-medical.netnews-medical.netnews-medical.netOpen source ↗

Each participant spent one night in the sleep laboratory with full overnight polysomnography. There were three groups: 30 cognitively unimpaired people without abnormal amyloid (mean age 63.7 years), 45 cognitively unimpaired people with abnormal amyloid, i.e. preclinical Alzheimer's (66.1 years), and 41 people with biomarker-confirmed mild cognitive impairment or mild dementia due to Alzheimer's (68.8 years). About 57% of participants were women, and group comparisons were adjusted for age and sex.

Changes in slow-wave shape

The clearest difference was in the shape of individual slow waves, which became flatter and lower across the three groups. The average slope fell from about 370 microvolts per second to 342 and then to 300. Peak-to-peak amplitude fell from about 100 microvolts to 95 and 89.5, while wave duration grew from 1.22 to 1.25 and 1.32 seconds.

Slope and amplitude changes were already visible in the amyloid-positive people without cognitive impairment. The authors write that it is not simply a reduction in the number of slow waves, but changes in their morphology, that mark the earliest signs of sleep-related deterioration. Slow-wave power was about 15–21% lower in early Alzheimer's than in the amyloid-negative group, depending on the frequency band. news-medical.netnews-medical.netnews-medical.netOpen source ↗

Sleep structure and cognition

Broader sleep changes appeared mainly in the symptomatic group. Wake after sleep onset averaged about 108 minutes versus roughly 61–64, sleep efficiency was 69% versus 79–83%, and latency to REM sleep was about 157 minutes versus 95–105. The two cognitively unimpaired groups did not differ significantly on these measures.

Among 76 cognitively unimpaired participants with follow-up over about six and a half years, steeper waves and greater amplitude were associated with better cognitive scores. The authors note that the group comparison is cross-sectional, so it cannot show whether sleep disturbance is a cause or a consequence. Sleep was recorded for only one night, and conclusions about differences between men and women are preliminary because the groups were small.