sleep epidemiology, genetics & neurophysiology

Brigham & Women's Hospital, Harvard Medical School, Boston

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Why sleep?
In the course of his or her life, the average person sleeps for more than 25 years. Despite major advances in understanding the circadian and homeostatic factors that regulate sleep, still much is unknown about its functions: the reasons why we sleep. Sleep is believed to play important roles across a broad range of processes, including memory consolidation, neuroprotective actions, hormonal function, and interactions with the cardiovascular and immune systems. Nonetheless, in many ways “sleep” currrently remains an umbrella term for a heterogeneous set of interacting processes that need to be better characterized and understood.
Individual differences in sleep
People vary considerably in their typical quality and quantity of sleep. On one level, brain activity as measured by the electroencephalogram (EEG) is a heritable “fingerprint”, aspects of which correlate with a range of clinical, demographic and cognitive variables. On another level, individuals suffering from disorders of sleep (including sleep apnea, insomnia, hypersomnia and narcolepsy) can exhibit markedly aberrant sleep patterns. The genetic bases for most of this clinically meaningful variability is largely unknown, however.
Sleep and health
Individual differences in sleep (especially lack of sleep) have been associated with a host of chronic medical conditions including obesity, diabetes, hypertension, heart disease and – ultimately – shortened life expectancy. For some disorders (e.g. major depressive disorder and bipolar disorder) sleep problems are core clinical features. The direction of these associations is typically unclear, however. Do sleep problems lead to disease, or disease to abnormal sleep? Or does a third factor – such as shared genetic basis – give rise to both sleep and health phenotypes? Delineating these types of causal networks will be important because it can provide a basis for identifying targets for intervention and patient stratification.

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