A state of the organism that occurs during dreaming, recently found to be physiologically distinct from both the ordinary sleep state (S-State) and the waking state (W-State).During an average night’s sleep, the individual goes through four or five periods in which rapid conjugate eye movements can be detected (REM) and EEG, or brain wave patterns, resemble those of wakefulness (Aserinsky and Kleitman, 1953). People who are awakened during these periods almost invariably report that they were dreaming. It also appears that dreaming takes place only during these states. Ordinarily these periods first appear about fifty to ninety minutes after the onset * of sleeping, occur periodically throughout the night, and occupy a total of about ninety minutes (PLATE 16).Many indices show that the organism is more active during the D-State than the S-State: increased pulse and respiratory rate, irregularity in these functions as well as in blood pressure, full or partial erection in 90 per cent of male subjects, an increase in brain temperature and oxygen intake, greater blood flow in the cortex, and especially sporadic brain wave patterns similar to those occurring when an object is followed with the eyes during the waking state.The D-State has been reported in all mammals fully tested, including sheep, dogs, cats, rabbits, and monkeys, but it has not been found in reptiles. The time spent in the D-State varies greatly. It occupies 20-60 per cent of the total sleep time in adult cats and only about 2 per cent in sheep (Jouvet et al., 1960; Jouvet and Valatx, 1962). The reasons for the variations are unknown, although there is evidence that species that live longer and have a lower metabolic rate have longer D- State periods. In human beings the average length is fourteen minutes, the longest of any species so far investigated. The total amount of time spent in the D-State, however, depends on the age of the organism. Studies made on cats, sheep, and men have shown that the young spend more time in the D-State that the adults (Jouvet et al., 1961; Roffwarg et al., 1964). In human beings, the total time spent in the D-State amounts to 45 to 65 per cent of the sleeping time among newborn infants, 20 to 25 per cent among eighteen- to twenty-year-olds, and 13 to 18 per cent among fifty- to seventy-year-olds. These figures seem to indicate that the D-State is more primitive than the W-State or the S-State.How essential is the D-State? To answer this question, Dement (1960) made a classic study of “dream state deprivation” in which human subjects were awakened every night for five nights as soon as the REM-State began. After this, the subjects were allowed five “recovery” nights of uninterrupted sleep. The experiment demonstrated that (1) only four to five interruptions were required to eliminate the D-State on the first night, but this number increased to twenty to thirty on the fifth night; (2) on the recovery night D-State activity comprised 30 to 40 per cent of the total S-Time, as if to make up for the lost D-Time; (3) even though the subjects obtained six to seven hours of sleep during the deprivation nights, they tended to be irritable and tense during the following day, as if they had gotten too little sleep.In a control study the same subjects were awakened the same amount of time from S-Sleep rather than D-Sleep, and they failed to show these emotional reactions the following day. As a further test, Dement extended the D-dep- rivation to fifteen days in three subjects (1963), and obtained the same results as above, but in exaggerated form. Toward the end of the experiment, it became almost impossible to awaken the subjects, and Dexedrine had to be administered. During the recovery period the time spent in the D-State rose to 60 per cent of the S-Time. Moreover, two of the subjects underwent distinct personality changes during the day, one of them giggling constantly and the other showing paranoid symptoms.Dement’s studies indicate that there is a basic need for the D-State, and probably for the psychological experience of dreaming itself, since it takes place during some and perhaps all of the D-State. It may well be that our physiological and mental health are both dependent upon it.The investigation of the effects of D-State deprivation on the personality has recently been extended to mentally disturbed patients.In spite of the fact that many specialists have noted that schizophrenics appear to be living in a dream, studies have shown that their waking state is physiologically similar to that of normal individuals, and their D-State during sleep occupies a normal amount of time. However, as Hartmann (1966) points out, their D-Periods are less sharply demarcated than among normals. He has also found that D-State deprivation may be involved in the onset of the psychosis, since these patients often report that they cannot sleep or that they sleep poorly during this period. The lack of sleep cuts down on the D-State time and leads to waking state difficulties—a situation that may produce a vicious cycle. What is needed, Hartmann suggests, is a drug that will induce sleep without interfering with D-Time. There is also evidence that borderline patients spend more time than usual in the D-State (Fisher and Dement, 1963), and there appears to be a significant correlation between D-State time and anxiety scores among college students (Rechtschaffen et al., 1964).Studies of the D-State have thrown new light on the nature of dreaming. Rechtschaffen et al. (1963) report that dreams occurring nearer to morning are more vivid and bizarre than dreams occurring earlier. Offenkrantz and Rechtschaffen (1963) found that successive dreams on the same night tend to express the same material in an increasingly clear and undisguised manner. External stimulation such as light or sound will become incorporated in a dream during the D-State, but will not induce a dream during S-Sleep (Dement and Wolpert, 1958). It has also been found that people who ordinarily do not recall their dreams will usually recall them if awakened during the D-State (Goodenough et al., 1959). A relationship between eye movements and the actual scene dreamed about has likewise been reported—when the scene was one in which a great deal of movement occurred, the eye movements tended to change more rapidly than in dreams involving little activity. Moreover, the muscle potentials recorded during dreaming appear to be an attenuated form of those occurring in actual behavior.Finally, considerable progress has been made on the physiological aspects of the dream-state. Through surgical intervention on animals, Jouvet and others have localized the pons (a structure in the brain stem) as the area most involved, and for this reason the D-State is often referred to as pontine sleep. The exact control center and specific circuits involved, however, have yet to be identified. The effects of drugs on the D-State is another area of physiological investigation. Barbiturates have been found to increase D-State time; alcohol, tranquilizers, and hypnogenic drugs decrease it. Murio et al. (1964), have shown that LSD may increase the length of the single D-Period but not increase total D-Time. As Hartmann (1966) suggests, it would be useful to have a drug that will increase total D-Time because of its importance in maintaining our psychological equilibrium. However, no such drug is presently available.