Cognitive Dysfunction in Insomnia Phenotypes: Further Evidence for Different Disorders.

Michelle Olaithe,Peter R Eastwood,Romola S Bucks,Nigel Mcardle,Sara Donaldson,Melissa Ree,Maria Pushpanathan

doi:10.3389/fpsyt.2021.688672

Abstract

Study Objectives: To determine cognitive profiles in individuals with short sleep duration insomnia (SSDI) and normal sleep duration insomnia (NSDI; also, paradoxical insomnia), compared to healthy sleepers.Method: Polysomnographic (PSG) and neuropsychological data were analysed from 902 community-based Raine Study participants aged 22 ± 0.6 years of whom 124 met criteria for insomnia (53 with NSDI and 71 with or SSDI) and 246 were classified as healthy with normal sleep (i.e., without insomnia or other sleep disorders). Measurements of self- report (attention and memory) and laboratory-assessed (attention, episodic memory, working memory, learning, and psychomotor function) cognition and mood, and PSG-based sleep stages (% total sleep time; %TST) were compared between these 3 groups.Results: In comparison to the healthy sleeper group, both insomnia groups had poorer self-reported attention, memory, mood, and sleep, and poorer laboratory-assessed attention (inconsistency). The NSDI group had less consistent working memory reaction time than healthy-sleepers or those with SSDI. The SSDI group had more inconsistency in executive function (shifting), and showed greater %TST in stage N1 and N3, and less REM sleep than either healthy-sleepers or those with NSDI.Conclusions: Individuals with NSDI demonstrated greater working memory inconsistency, despite no laboratory assessed sleep problems, implicating early signs of pathophysiology other than disturbed sleep. Those with SSDI demonstrated different sleep architecture, poorer attention (inconsistency), and greater executive function (inconsistency) compared to healthy-sleepers and those with NSDI, implicating sleep disturbance in the disease process of this phenotype.

Highlights

Insomnia is a highly prevalent sleep disorder [1], characterised by self-reported dissatisfaction with sleep quality or quantity, frequently expressed as difficulty initiating or maintaining sleep, or experiencing non-restorative sleep over many days, and accompanied by significant distress or daytime impairment [2]
TST, total sleep time; SE, sleep efficiency; ESS, Epworth sleepiness scale; PSQI, Pittsburgh sleep quality index; TST and SE values are taken from overnight sleep study; *indicates that the marked group showed a significant difference to the healthy sleepers group. ∧indicates a significant difference between the normal sleep duration (NSDI) and short sleep duration (SSDI) groups. These data show that the cohort was relatively young (22-yrs), that lab-assessed sleep efficiency was poor in those with SSDI, and that both phenotypes reported high levels of sleepiness, and low levels of sleep quality
Post-hoc comparisons indicated that participants with SSDI spent a larger percentage of TST in N1 compared to the healthy sleepers [p < 0.001; Cohen’s d = 0.39] and to those with NSDI [p < 0.001; Cohen’s d = 0.67]

Summary

Introduction

Insomnia is a highly prevalent sleep disorder [1], characterised by self-reported dissatisfaction with sleep quality or quantity, frequently expressed as difficulty initiating or maintaining sleep, or experiencing non-restorative sleep over many days, and accompanied by significant distress or daytime impairment [2]. Risk factors for developing insomnia include female gender, older age, and chronic illness or pain [3]. Consequences include an increased risk of accidents, poorer work productivity, higher pain levels, and more emotional and mental health problems [5]. In a recent systematic review and meta-analysis of insomnia and cognitive performance, Wardle-Pinkston et al [6] reported small to medium differences in the cognitive domains of complex attention, working memory, episodic memory, and executive function between individuals with and without insomnia. An earlier meta-analysis by Fortier-Brochu et al [8] reported small to medium effects for episodic memory, working memory, and executive functions (problem solving), whilst finding no differences in attention. An investigation by Ballesio et al [9], focussing on executive functions, found small effects for reaction times, but not accuracy, in the subdomains of inhibition, flexibility, and working memory

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