Poor sleep quality might cause cognitive difficulties, while REM sleep might be protective against these difficulties, highlighting the usefulness of a simple neurocognitive screening tool for patients with persistent insomnia disorder (pID).
In patients with persistent insomnia disorder (pID), a simple neurocognitive screening tool found that these patients showed cognitive deficiencies that related to both subjective/self-reported and objective/polysomnographic measures of sleep quality, according to Nature and Science of Sleep.
Additionally, those cognitive changes looked like those observed in preclinical non-amnestic Alzheimer disease (AD) and could suggest incumbent neurodegenerative processes in pID.
Intriguingly, increased REM-sleep was correlated with improved cognitive performance, but whether REM sleep is protective against neurodegeneration needed more investigation.
This study was conducted because pID is associated to neurocognitive decline and increased risk of AD in later life, but research in this field usually uses self-reported sleep quality data that may be biased by sleep misperception or uses extensive neurocognitive test batteries that are not often feasible in clinical settings.
The goal of this study was to evaluate if a simple screening tool could reveal a precise pattern of cognitive changes in patients with pID, and if these relate to objective aspect(s) of sleep quality.
“Changes in sleep patterns are closely linked to neurodegenerative processes, and are a common comorbidity in patients with dementing illnesses like [AD]. This relationship between sleep quality and neurodegeneration is bi-directional, and several brain regions involved in regulating the sleep-wake cycle are important for cognitive functions,” said the study authors.
First, data were collected on neurocognitive performance (Montreal Cognitive Assessment; McCa), anxiety/depression severity, and subjective sleep quality (Pittsburgh Sleep Quality Indez [PSQI]; Insomnia Severity Index [ISI]) from 22 middle-aged patients with pID 22 good sleepers. Patients underwent polysomnography overnight.
It was found that patients with pID had lower overall cognitive performance (average, 24.6 vs 26.3 points; Mann-Whitney U = 136.5; P = < .006) compared to good sleepers, with deficits in clock drawing and verbal abstraction. Also in patients with pID, worse overall cognitive performance correlated with decreased subjective sleep quality (PSQI: r(42) = –.47; P = .001; ISI: r(42) = –.43; P = .004), reduced objective sleep quality (lower sleep efficiency: r(20) = .59; P = .004; less REM-sleep: r(20) = .52; P =.013; increased sleep latency: r(20) = .57; P = .005; and time awake: r(20) = –.59; P = .004). Cognitive performance had no relation to anxiety/depression scores.
Clock drawing is able to detect patients with an increased risk of dementia on its own, and a 22-year prospective study found that verbal abstract reasoning was one of the strongest predictors for the development of Alzheimer disease in the preclinical phase, so that specific deficit pattern could indicate an incipient neurodegenerative process.
The present study results showed that cognitive performance as also associated with objective polysomnographic sleep measures in patients with pID and go beyond just lower cognitive performance being linked to worse subjective sleep.
No evidence was found by the study authors connective cognitive performance and deep (slow-wave) sleep, and arousal/sleep-stage transition indices (reflective of sleep fragmentation). Instead, increased REM-sleep was connected to better cognitive performance, potentially displaying a protective role against cognitive decline.
This study is the first to the study authors’ knowledge to show increased REM-sleep as a possible protective factor against cognitive decline in patients with pID.
One limitation of this study is that polysomnographic data were not collected from controls, and so intergroup differences in sleep quality couldn’t be quantified. Additionally, patients didn’t have an acclimatization night, and might have experienced worse sleep because of the “first-night-effect.”
“Taken together, neurocognitive deficits can be identified in patients with pID using a simple screening tool. Furthermore, insomnia severity and the amount of REM-sleep are closes related to these deficits. Whilst these results demonstrate that a screening tool may be sufficient in identifying patients at risk, this would nevertheless need verification through a longitudinal study,” concluded the study authors.
Künstler ECS, Bublak P, Finke K, et al. The relationship between cognitive impairments and sleep quality measures in persistent insomnia disorder. Nat Sci Sleep. 2023;15:491-498. doi:10.2147/NSS.S399644