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.