The biological purpose of the dream

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    It has been repeatedly stated that the "purpose of the dream is to preserve sleep." The anxiety dream is looked upon as a result of failure of the dream work. Accordingly, it is held that when unacceptable id wishes approach the level of awareness, the ego interrupts sleep rather than permit the dream to go on. The state- ment as a whole seems teleological and in the final analysis con- tradictory.

    Were the only purpose of the dream the preservation of sleep, this purpose would best be served if we did not dream at all. Fur- ther, to ascribe a positive action to a failure of a mechanism, would be like explaining the speed of a racing car by the fact that its brakes do not hold. There is one essential characteristic of the anxiety dream which demands a more adequate explanation, and that is the fact that, in awakening from such a dream, the indi- vidual is abruptly placed in a condition of acute awareness of the environment, in contradistinction to more normal awakening. This must serve some phylogenetically-significant biological function.

    Sleep performs an essential physiological purpose. Without it, we eventually become exhausted and die. However, in sleep, the organism is less capable than when awake of protecting itself against environmental dangers. Animals, before going into a sleep, or sleep-like condition, instinctively protect themselves. Bears, which cannot be aroused in their winter sleep, choose as their hibernacula, refuges as inaccessible and as safe as possible from danger. This pattern of behavior is an inherited one and carries with it a survival value. Any failure in this pattern may be punishable by death and eradication of the individual in the strug- gle for survival. The best-adapted patterns of behavior best pro- tect the individual and hence are apt to be inherited.

    In other animals where sleep is of shorter duration and less pro- found, other protective measures play a role. The sleeping dog cocks an ear and raises an eyelid when there is a step in his direc- tion. If no danger is imminent, sleep is resumed. Otherwise, the animal is on guard and fully awake. Involved here, must be a men-

  • IVs BRODY~ 1~r163 D. 65

    tal mechanism which operates not only to preserve sleep, but which also acts to keep the sleep from being too profound, and which is ready to interrupt sleep completely in the presence of danger. This mental mechanism must be capable of interpreting stimuli which reach it, attenuating most of them and hence permitting sleep to continue, but ready at any moment to cathex strongly any. significant stimulus, and--like the alarm of the guard on duty when the post is asleep---instantly arouse the organism to defense. Fur- ther, sleep is never permitted to be so intense that potential re- sponse to stimuli ceases. In civilized man, no external dangers exist to the same degree as in the animal--except in combat situa- tions and the like--and the major dangers that can disturb the or- ganism arise from the unconscious.

    The foregoing may seem superficially to contradict basic psycho- analytic concepts. Actually, the reverse is true. A much broader biological significance is given to the dream.

    In summary, it would seem closer to the truth to postulate that the dream is part of a complex mental mechanism that at night regulates (rather than preserves) sleep; that this mental mechan- ism is as much concerned with preventing the depth of sleep from becoming too profound as with preventing it from becoming too shallow; that one of its functions, phylogenetically, is that of pro- tecting the organism from danger, either from within or without; and that in the civilized state, practically the sole source of danger is in the Unconscious.

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