Biological Rhythms, Sleep and Cognition in Mood Disorders

Abstract

This thesis presents research investigating the relationship between, and methods of, measuring circadian rhythms in mood disorders in a population of currently depressed and euthymic individuals with both depression and bipolar disorder. This was first assessed by comparing group differences in subjective sleep and circadian measures with objective sleep and circadian measures. The objective circadian measures involved actigraphy and melatonin profiling. This analysis showed group differences in subjective sleep and circadian parameters compared to controls, however no robust differences between mood groups. Objective melatonin profiling showed a mild agreement with subjective circadian parameters. Next, we studied the external validity of a subjective rating scale measuring biological rhythm disturbance, the Biological Rhythms Interview for Assessment in Neuropsychiatry (BRIAN), against objective measures of sleep and circadian activity rhythmicity. The BRIAN demonstrated some promising external validity, namely correlations with wake after sleep onset (WASO) and sleep efficiency, as well as melatonin levels in each group. These studies provide evidence of the extent to which a self-report may help in assessing parameters of sleep and circadian rhythms in the clinical setting. In doing so, it is expected that the use of subjective ratings will provide insight into the impact of biological rhythms disturbances and mood disorders. Lastly, we conducted an overview of the preclinical and clinical literature investigating the impact of circadian disturbance on cognitive performance. The results from this literature review yielded patterns of rhythmicity in specific parameters in each of the attention, memory, and executive function domains in humans, whereas attention and memory are more of a primary focus in animal studies. However, we also found that there are significant gaps in the understanding of how disturbances in circadian rhythms may influence cognitive function. This review also highlights the importance of cross-species translational validity from a methodological perspective, in order to generate positive clinical results beginning at the preclinical stage in neuropsychiatric disorders.