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1 Introduction
As long as we do not know how and why sleep forces on us a necessary
and recurrent change in the process of our relations with our environment,
it is impossible to give a definition of sleep that would satisfy everybody.
Indeed the causes and mechanisms of sleep remain unknown despite a great
amount of work. Kleitman's huge book (277)
itself includes 4,377 references, and yet the latest achievements in the
neurophysiology of sleep have only limited coverage. Since it is thus
out of the question to undertake a general survey of the physiology of
sleep, this paper is limited to a review of some particular aspects of
the neurophysiology of sleep in the light of results achieved in the last
5 or 6 years. On the one hand, we must assume that our brain, like our
kidneys and heart but unlike our muscular system, does not rest during
sleep. On the contrary, it undergoes an active reorganization rather than
a real inhibition, and so sleep seems to be an active phenomenon. On the
other hand, it appears that behavioral sleep does not proceed from a single
process but is the manifestation of two different states of nervous activity,
though these are closely interconnected. The electrical brain activity
of a sleeping mammal has a recurring evolution proceeding from two opposite
modes. The first mode, which is the earliest known (and which is called
slow sleep), manifests itself in the presence of a synchronized cortical
activity of spindles and/or of high-voltage slow waves. The other mode
reveals itself by a low-voltage fast cortical activity similar to arousal
activity [activated sleep (122)
or paradoxical or rhombencephalic sleep tPS) (254)].
Though it has not yet been proved that these two electric aspects of sleep
are the manifestation of a single hypnogenic mechanism or the manifestation
of two fundamentally different states, I shall set forth their behavioral
and electric aspects successively and then discuss the mechanism of their
appearance the last chapter is devoted to their respective interrelations
in the light of their phylo- and ontogenetic evolution. I shall not deal
in detail with the problems of vegetative, respiratory, digestive, blood,
or metabolic (267) variations
during sleep for they are clearly stated by Kleitman (277);
this study is also limited to the nervous theories of sleep state, though
humoral theories are again of topical interest (279,
319, 320).
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