ABSTRACT
The two primitive motivations of pain and hunger are regarded as mainly determined by specific bodily conditions tissue damage and lack of nourishment. A third motivation, biologically primitive, is that of sex. It has been clearly shown that the arousal of sex behavior does not depend on any particular sensory stimulation. A behavioral excitation, an increase in some bodily activity, is not necessarily a sign of an increased neural activity either in the brain as a whole or in some one part of it. The term deafferentation may overemphasize the role of sensation in the sleep cycle of the normal animal. Kleitman considers that the sleep cycle of the adult is a function of learning and in old age, when other learned behavior is deteriorating, we find the cycle also tending to return to a more infantile stage. Habituation to monotony is apt to be accompanied by complex daydreaming, which means the development of a parallel phase-sequence activity.
