ABSTRACT
Bipolar illness is, by definition, a cycling disorder. The longitudinal course is characterized by recurrent episodes of depression and mania or hypomania, with intervening periods of euthymia (1). The fact that cyclicity is a salient feature of the clinical phenotype has led many investigators to speculate that abnormalities in biological rhythms might prove etiologically or pathophysiologically significant in the disease process, and several lines of evidence support a relationship between biological rhythm disturbances in the onset and maintenance of bipolar episodes. Notably, physiological and behavioral timekeeping processes are often altered in bipolar patients, and there is evidence to suggest that a susceptibility to biological rhythm instability may be a factor in the onset and maintenance of affective episodes. For some patients, interventions that serve to stabilize or resynchronize sleep and biological rhythms prove therapeutically effective. Furthermore, sleep propensity is markedly altered during different phases of the disorder, and sleep disturbance is perhaps the most potent predictor of mood deterioration. Lastly, although quite preliminary, several recent studies have attempted to identify mutations in genes involved in circadian clock regulation that might influence the disease process in a subgroup of patients. The prevalence of biological rhythm dysfunction in bipolar disorder, the cyclical presentation of symptoms, and the strong link between sleep disturbance and episodes of mania and depression suggest that these features are pathophysiologically important in the disease process and might inform treatment development for this illness. This chapter will review these areas of research in bipolar illness.
