The Functions of Sleep

Scientists investigating sleep claim complete ignorance about its function and have called it the arcanum arcanorum, the mystery of mysteries (King, 1970); yet every layman knows that the function of sleep is to “restore,” to “make you feel better.”

I shall attempt here to make scientific sense out of this lay view and to present a coherent and, I hope, testable theory of the functions of sleep, drawn from clinical experience and interview studies, as well as from a number of human and animal experiments in my sleep laboratory.

Freud (1900) speaks in general of a restorative function of sleep and mentions, in the topographic model, that it is the preconscious which requires sleep. Further, since censorship is relaxed during sleep, Freud suggests that one function of sleep is to allow the periodic emergence of unconscious repressed material from the id, i.e., to allow the drive discharge that characterizes dreaming. These are about the only hints as to a possible functional role of sleep in Freud's work, and, in fact, he specifically states that the function of sleep will probably turn out to be a biological rather than a psychological problem (1900).

In order to arrive at a view of function—of what may need to be “restored” by sleep, and how sleep can restore it—it will be necessary to examine the following questions: Is there such a thing as a requirement for sleep? Who requires how much sleep? (I.e., What characterizes people who need unusual amounts of sleep?) When does a given individual require more or less sleep? What experimental manipulations can increase or decrease sleep requirement? What changes occur during sleep deprivation? What in the psyche or in the brain actually requires restoration by sleep? These approaches to the functions of sleep, and several others, are presented in detail elsewhere (Hartmann, 1973).

The present discussion will consider briefly each of these questions and in addition will attempt to clarify the psychology or metapsychology of ti