The physiological basis of sleep including its importance was reviewed and discussed.
Among the definitions of sleep, Hobson’s definition is most reasonable. The reason is that it
contains both result of recent progress of sleep science and brain research. It rephrases
Abraham Lincoln’s famous declaration about government : “Sleep is of the brain, by the
brain, and for the brain”. Sleep has been thought formally under the unitary theory, but
presently under the duality theory. It is due to the two epoch-making discoveries : one is
that of EEG and the other is that of rapid eye movement (REM) sleep. Scientific research of
sleep was opened by these two discoveries. There are two kinds of states, non-REM sleep
and REM sleep, in sleep of higher animals including humans. Those sleep states are defined
with EEG, EMG, and eye movements. There are common phenomena of “behaviorally defined
sleep” to those of human sleep in the lower animals such as insects, fishes, amphibians, and
reptiles. However, there is the characteristic feature in human sleep which is not observed
in the lower animals. When conducting an animal experiment, it is necessary to recognize
this point. Sleep is regulated under the two control systems : biological clock and homeostasis.
As a brain part adjusting sleep and wake, the whole aspect is not yet disclosed, although the
special neural network which contains the basal forebrain including the diencephalon
(thalamus and hypothalamus) and the brain stem (midbrain, pons, and medulla oblongata) is
important. As to these neural mechanisms, relation of the humoral mechanism by the sleep
substance, neurotransmitter, etc. has been clarified recently, and it is thought that both the
neural and humoral mechanisms exert the complement-action on the mutual regulation of
sleep and wake. Recently, the method of approaching sleep in molecular biology has been
budding.
In conclusion, it is sleep that is easy to fall victim among everyday life in “24-hour
society.” As the price at the sacrifice of sleep, not only a health trouble, but also a social
problem and an economical loss are caused. The role of sleep, a basic physiological function,
should be greatly appreciated. Sleep, with wake, is the physiological basis of our behavior
and supports our life activity from both dynamic and static sides, alternately and mutually.
Both sleep and wake are regulated by the brain, fitting our living body to internal and
external environment. Sleep is food of the brain and essential to the health of our mind and
body
