The objective nature of sleep-wake and circadian rhythms in young people with affective disorders

Abstract

Affective disorders are associated with various disturbances in sleep-wake and circadian rhythms including disruptions in sleep, abnormal timing of sleep and wake, and abnormalities in circadian patterns of activity, hormone secretion, and temperature regulation. However, there is a large degree of heterogeneity across studies, with some conflicting results and considerable individual variation. Adolescence and young adulthood is a period of significant change in sleep-wake and circadian rhythms as well as a key period for affective disorder onset. This thesis aimed to investigate the nature of sleep-wake and circadian disturbances in young people with affective disorders in order to provide a better understanding of the mechanisms by which circadian dysfunction may contribute to affective pathology. A transdiagnostic approach was taken across three empirical studies of young people presenting for care for affective disorders. Measures included actigraphy, in-lab assessment of evening melatonin and overnight core body temperature, neuropsychological assessment, and magnetic resonance imaging of pineal gland structure. Cluster analysis identified three distinct groups based on sleep-wake parameters from actigraphy recording, defined by ‘long sleep’, ‘disrupted sleep’, and ‘delayed sleep’. Three distinct groups were also identified based on circadian actigraphy parameters defined by ‘strong’, ‘weak’, and ‘delayed’ circadian activity rhythms. Visual memory was somewhat impaired in the long sleep group, and the delayed sleep group presented with delayed evening melatonin onset and core temperature nadir. A positive association between pineal volume and evening melatonin secretion was found, similar to that found in previous healthy samples. The key implications of this research are that different biological circadian disturbances may to lead to different sleep-wake abnormalities in young people with affective disorders, with potential different treatment indications.