Historical Background

Dreaming is a complex psychobiological function, that eludes a precise and universally shared definition.

Research into this important dimension of the human mind is continually evolving, and despite the fact that much progress has been made, we are still a long way from a satisfactory understanding of its biological and psychological implications.

Given the peculiar methodological limitations of the research in this area, it is worth presenting an overview of our current knowledge in a historical perspective. I hope it will allow the reader to better judge the validity and the possible lines of development of the field.

In the antiquity, sleep had a dual significance. On the one hand, it symbolized death, in the abandonment of the limbs and in shutting oneself away from the experience of the senses (Hesiod's Theogony depicted Sleep and Death as two brothers); on the other hand, sleep was like a door that, through the secret pathways of dreams, led to a dimension beyond intelligence and enabled humans to come into contact with the supernatural.

Even on a philosophical level, there were two somewhat opposite orientations that can still be recognized in some of today's scientific views. Some thinkers viewed sleep as a passive withdrawal from consciousness and dreaming was thus an illusion or a nonsense; according to others, sleep represented the theater of a different form of mental activity and dreams bore meanings.

In Sleep and Wake (453 bc), Aristotle defined sleep, and what takes place in it, as a "privation of wakefulness,'' i.e., as a purely negative concept—a pause in human sensory experience and intellectual functioning. During sleep, either intelligence is silent and everything is dark or it is deceived by a flow of disconnected fleeting images that give rise to dreams.

In Republic, Plato discussed the obscure depths of the psyche that are revealed through nocturnal dreams. Not only may the gods reveal themselves to man through dreams but also in the same way man reveals himself to himself. Even Heraclitus seems to hint at a different orientation of the psyche in the transition from wakefulness to sleep: "He who is awake lives in a single world common to all; he who is asleep retires to his own particular world.''

Over the centuries, dreaming aroused more the curiosity than the systematic interest of researchers. The views of 19th-century neurophysiologists, strongly influenced by positivistic thought, essentially adhered to the original Aristotelian lines.

As a matter of fact, until recently, states of consciousness were believed to vary along one continuous dimension in parallel with behavioral performance, from deep coma to the opposite extreme of manic excitement. In this view, rational thought appeared as a form of mental activity exclusively belonging to waking states, whereas dreaming was simply the expression of the fragmentation and dissolution of thought, in close relationship with the lowering of vigilance and the deepening of sleep.

Only toward the end of the 19th century were some contributions made that considered dreaming an event deserving direct attention. The observations of two French scholars, the Marquis d'Hervey de Saint-Denis and Alfred Maury, are worth mentioning here, along with those of the initiator of experimental psychology, the German Wilhelm Wundt. However, the contribution that truly catalyzed the attention of contemporary culture was the brainchild of a scholar, Sigmund Freud, who had no real connection with the emerging experimental psychology approaches. Freud pointed out a methodological flaw in the way those who considered dreaming a completely meaningless activity examined the oneiric content. Researchers were trying to understand dreams according to the same register that was used for comprehending "normal" language instead of searching for the appropriate key to decrypt a language that is quite peculiar. According to Freud, this was like expecting to understand a rebus, with its apparently bizarre compositions, by reading it as a common rational message.

Freud's book on the interpretation of dreams, which was published in 1900, is a cornerstone in psychoanalytical theory and a significant historical event in contemporary culture. However, it is well-known that Freudian studies mainly focused on the contents of the phenomenon, whereas the proposed functional explanations suffered from the poor knowledge at the time of the central nervous system's physiology and of the organization of the mind in general, matters brought to the forefront of research by modern neuroscience.

In order to probe the functional basis of dreaming, it was necessary to shed light on objective, measurable aspects, such as the frequency and periodicity of dreaming, its universality, episodic and total duration throughout the night, and especially its neurophysio-logical regulation. The first step in solving these and other general problems was the discovery of some objective indicators that could reveal the presence of the dream itself.

As sometimes happens in science, the first curtain protecting the mystery of dreaming was lifted almost by chance by a young student working on his doctoral thesis in the early 1950s. Studying attention in children, under the supervision of Nathaniel Kleitman at the University of Chicago, Eugene Aserinsky observed that sometime after the onset of sleep, the subjects' eyes could be observed, under the closed eyelids, moving left and right and up and down while all the major body movements ceased. After several minutes, these eye movements would stop altogether, only to resume again with the same characteristics at more or less regular intervals throughout the night. Since the pattern of eye movements resembled that of an awake subject exploring a visual scene with his or her gaze, the hypothesis was put forward that dreaming occurs in these periods.

To test the hypothesis, the experimenters set out to awaken and question subjects at various times during the night. In most cases, subjects were able to report dream content when awakened during periods of eye movements, whereas they could rarely recall dreams if awakened while their eyes did not move. The results seemed to clearly confirm the conjecture, and Aser-insky's accidental observation took on the proportions of a profound scientific discovery.

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