The impacts of insomnia on cognitive functioning in adolescents and young adults

Abstract

Insomnia is the most prevalent sleep problem affecting up to 40% of the youth population, which entails adverse outcomes, including impaired physical health, psychological and behavioural problems, and cognitive impairments. There is much evidence suggesting the negative impacts of insomnia on cognitive functioning in adults. However, there is a lack of research in youths, especially on the neural correlates of cognitive impairments associated with insomnia. In this thesis, the impacts of insomnia on cognitive functioning among youths were investigated in four studies.

Study 1 was a cross-sectional study that involved 190 adolescents and young adults recruited from local secondary schools and universities. Participants completed self-reported questionnaires to assess insomnia severity and self-perceived memory performance, a 7-day actigraphic assessment to measure their habitual sleep, and cognitive tasks to assess memory functioning objectively. The results indicated that the presence of insomnia symptoms, rather than objective short sleep duration, was associated with both poorer self-perceived memory abilities and poorer performance on a working memory task.

Study 2 was a case-control study that examined the neural correlates of inhibitory control in youths with insomnia using electroencephalography (EEG). Twenty-eight participants with DSM-5 insomnia disorder and 31 healthy sleepers aged between 15-25 completed the study. Time domain and Time-frequency domain analyses were conducted on the EEG activities during the Cued Go/No-go (CGNG) task, designed to assess inhibitory control. The results suggested that youths with insomnia demonstrated altered brain activity during inhibitory control, despite their comparable behavioural performance.

Study 3 was a case-control study that examined reward processing using EEG during the Door task, a monetary reward task. Participants from Study 2 also took part in Study 3. Reward processing was indicated by event-related potential (ERP) component named the reward positivity (RewP). The insomnia group showed more blunted RewP than the healthy sleeper group, demonstrating reward dysfunction in insomnia.

Study 4 was a secondary analysis of two clinical trials that investigated whether treatment of insomnia would result in improved cognitive performance. A total of 124 youths with DSM-5 insomnia disorder were included in the analysis. Participants were assigned to either cognitive behavioural therapy for insomnia (CBT-I; N = 58) or waitlist (N = 66). Cognitive functioning was assessed by a self-report questionnaire and a battery of objective cognitive tasks at baseline and one week after treatment/waitlist period. There was evidence supporting the effects of CBT-I on improving self-perceived cognitive functioning. However, there were no differences in other aspects of cognitive abilities in terms of working memory, inhibitory control, set shifting, and abstract reasoning between the two groups.

To conclude, insomnia is associated with cognitive detriments as evidenced by self-report, behavioural performance, and neurophysiological measures. CBT-I could lead to improvements in some aspects of cognitive functioning in youths with insomnia disorder. Future research is needed to further delineate the long-term impacts of insomnia on other domains of neurocognitive functioning and academic achievements in adolescents and young adults.