Executive functions impairments in insomnia: A systematic review and meta-analysis.

Introduction: Executive functions (EFs) are a family of top-down processes involved in the control of affect and cognition. Influential models assume the presence of three core EFs: inhibitory control, working memory and cognitive flexibility. Research on these three functions in patients with insomnia has yielded mixed results. Therefore, we performed a systematic review of the literature on the three EFs of inhibitory control, working memory and cognitive flexibility in adults with a diagnosis of insomnia in order to clarify the presence and magnitude of EFs impairments in this population. Materials and methods: PubMed, Scopus, Medline and PsycINFO were searched from inception to 2015. Inclusion criteria were: presence of a group of adult individuals with clinical insomnia, presence of a control group, presence of at least one neuropsychological test assessing inhibitory control and/or working memory and/or cognitive flexibility. Included studies underwent quality assessment. Findings were summarized using combined narrative synthesis and meta-analysis. Cohen's d were calculated at 95% confidence interval as effect sizes of between groups differences. Heterogeneity of effects distribution as well as publication bias were evaluated. Results: Twenty-four studies met the eligibility criteria and were included. Results showed impaired performance of individuals with insomnia as compared to controls on tasks of inhibitory control with an effect of small to medium magnitude (d= .31, 95% CI: .50 – .11) and homogeneous distribution (Q= 3.356, df= 8, p= 0.910; I2= 0.000). Visual examination of the funnel plot suggested reasonable symmetry indicating low chance of publication bias. We were limited in performing meta-analyses on working memory and cognitive flexibility due to the small number of studies and high variability of outcome measures. Conclusions: Using meta-analysis, we showed that individuals with insomnia perform poorer than good sleepers on tasks of inhibitory control. Due to the high variability of outcome measures and small number of studies, we were not able to statistically estimate the magnitude of impairments with respect to working memory and cognitive flexibility tasks. To overcome these limitations and advance knowledge of EFs in insomnia, future studies are warranted adopting comparable outcome measures.