Freud, S. (1914). Remembering, repeating, and working-through. In The standard edition of the complete psychological works of Sigmund Freud. London: Hogarth Press. Reik, T. (1948). Listening with the third ear: The inner experience of a psychoanalyst. New York: Farrar, Straus. Reik, T. (1964). Voices from the inaudible: The patients speak. New York: Farrar, Straus.


THIRST, THEORIES OF. The term thirst may be defined operationally as the internal, physiological state that results from water deprivation for a given period of time and is usually characterized by dryness in the mouth, throat, and mucous membranes of the pharynx. In terms of motivation, the concept of thirst is a need/drive state resulting from liquid deprivation that produces a desire for fluids, specifically water, and motivates water-seeking behavior. An early peripheral theory of thirst, called the dry-mouth theory - proposed by the American physiologist Walter Bradford Cannon (1871-1945) - emphasizes the relationship of salivary-gland function and moisture receptors in the mouth. The common notion that drinking results simply when the mouth is dry has a long history going back to Hippocrates (c. 460-377 B.C.). The dry-mouth theory of thirst was revived later in the 18th century by the Swiss physiologist Albrecht von Haller (1708-1777) and continued to enjoy great popularity because of its intuitive appeal. Cannon's dry-mouth theory, or local theory of thirst, however, has not survived the test of time and experimentation. For example, the removal of the salivary glands in dogs does not disrupt the regulation of water intake in terms of the amount of liquid consumed, nor does the administration of drugs that induce excessive salivation. Severing the nerves associated with the mouth and throat appears, also, to be ineffective in amount of liquid consumed. The organism's need for water is metered by brain mechanisms that give rise to the sensation of thirst when the body's water stores become depleted. The brain seems to be sensitive to at least two different signals: (1) short periods of water deprivation result primarily in a loss of water from the general circulation system producing a state of low volume (called hypovolemia) and low blood pressure; and (2) with long periods of deprivation, water is drawn out of the cells to compensate for the critically low volume in the circulatory system, where prolonged deprivation and cellular dehydration accounts for 6570 percent of the body's water loss with vascular hypovolemia accounting for the remaining 30-35 percent of the loss (cf., hemorrhage and thirst hypothesis - posits that loss of blood increases thirst; however, experiments with animals yields inconclusive and equivo-cal results regarding this theory). A multifactor theory of thirst (cf., Adolph, Barker, & Hoy, 1954) takes such cellular dehydration effects into account. Based on the distinction between intracellular and extracellular fluids, two kinds of thirst may be considered: cellular dehydration thirst and hypovolemic thirst. A current view of water regulation, called the double-depletion hypothesis of thirst (cf., Epstein, 1973), is that although cellular dehydration thirst and hypovolemic thirst are often present together, they are independent regulatory activities with independent neural systems in control. However, the neural systems for cellular dehydration and hypovolemic thirst are both disrupted after extensive lesions of the lateral hypothalamus. Also, the relative contributions of peripheral factors, cellular dehydration factors, and hypovolemic factors ap pear to vary according to the species being studied. See also HUNGER, THEORIES OF. REFERENCES

Haller, A. (1757-1766). Elementa physiolo-giae corporis humani. Paris: Guillyn.

Murchison (Ed.), Handbook of general experimental psychology. Worcester, MA: Clark University Press. Adolph, E., Barker, J., & Hoy, P. (1954). Multiple factors in thirst. American Journal of Physiology, 178, 538562.

Adolph, E. (1964). Regulation of body water content through water injection. In M. Wayner (Ed.), Thirst. New York: Macmillan.

Epstein, A. (1973). Epilogue: Retrospect and prognosis. In A. Epstein, H. Kis-sileff, & E. Stellar (Eds.), The neu-ropsychology of thirst: New findings and advances in concepts. Washington, D.C.: Hemisphere. Grossman, S. (1975). Role of the hypothalamus in the regulation of food and water intake. Psychological Review, 82, 200-224. Stricker, E. (1990). Handbook of behavioral neurobiology. Vol. 10. Neurobiol-ogy of food and fluid intake. New York: Plenum Press.

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