Tales Of Dim Eden

Very old are we men; Our dreams are tales Told in dim Eden . .

WALTER DE LA MARE "All That's Past"

"Well, at any rate it's a great comfort," she said as she stepped under the trees, "after being so hot to get into the-into the-into what?" she went on, rather surprised at not being able to think of the word. "I mean to get under the-under the-under this, you know!" putting her hand on the trunk of the tree. "What does it call itself, I wonder?" . . . And now, who am I? I will remember, if I can! I'm determined to do it!" But being determined didn't help her much, and all she could say, after a great deal of puzzling, was "L, I know it begins with L!" LEWIS CARROLL Alice Through the Looking Glass

Come not between the dragon and his wrath. WM. SHAKESPEARE King Lear

Senseless as beasts I gave men sense, possessed them of mind

In the beginning, seeing, they saw amiss, and hearing, heard not, but like phantoms huddled In dreams, the perplexed story of their days Confounded.

AESCHYLUS Prometheus Bound

PROMETHEUS is in a fit of righteous indignation. He has introduced civilization to a befuddled and superstitious mankind, and for his pains Zeus has chained him to a rock and set a vulture to pluck at his liver. In the passage following the above quotation, Prometheus describes the principal gifts, other than fire, that he has bestowed on mankind. They are, in order: astronomy; mathematics; writing; the domestication of animals; the invention of chariots, sailing ships and medicine; and the discovery of divination by dreams and other methods. The final gift strikes the modern ear as odd. Along with the account in

Genesis of the exile from Eden, Prometheus Bound seems to be one of the major works in Western literature that presents a viable allegory of the evolution of man- although in this case concentrating much more on the "evolver" than on the evolved. "Prometheus" is Greek for "foresight," that quality claimed to reside in the frontal lobes of the neocortex; and foresight and anxiety are both present in Aeschylus' character portrait.

What is the connection between dreams and the evolution of man? Aeschylus is perhaps saying that our prehuman ancestors lived their waking lives in a state akin to our dreaming lives; and that one of the principal benefits of the development of human intelligence is our ability to understand the true nature and import of dreams.

There are, it seems, three principal states of mind in human beings: waking, sleeping and dreaming. An electroencephalograph, which detects brain waves, records quite distinct patterns of electrical activity in the brain during these three states.* Brain waves represent very small currents and voltages produced by the electrical circuitry of the brain. Typical strengths of such brain-wave signals are measured in microvolts. Typical frequencies are between 1 and about 20 Hertz (or cycles per second)-less than the familiar 60 cycles per second frequency of alternating currents in electrical outlets in North America.

But what is sleep good for? There is no doubt that if we stay up too long the body generates neurochemicals that literally force us to go to sleep. Sleep-deprived animals generate such molecules in their cerebrospinal fluid, and the cerebrospinal fluid of sleep-deprived animals induces sleep when injected into other animals who are perfectly wide awake. There must, then, be a very powerful reason for sleep.

The conventional answer of physiology and folk medicine alike is that sleep has a restorative effect; it is an opportunity for the body to perform mental and physical housekeeping away from the needs of daily living. But the actual evidence for this view, apart from its common-sense plausibility, seems to be sparse.

Furthermore, there are some worrisome aspects about the contention. For example, an animal is exceptionally vulnerable when sleeping. Granted that most animals sleep in nests, caves, holes in trees or logs or otherwise recessed or camouflaged locations. Even so, their helplessness while asleep remains high. Our nocturnal vulnerability is very evident; the Greeks recognized Morpheus and Thanatos, the gods of sleep and death, as brothers.

Unless there is some exceptionally strong biological necessity for sleep, natural selection would have evolved beasts that sleep not. While there are some animals- the two-toed sloth, the armadillo, the opossum, and the bat-that, at least in states of seasonal torpor, sleep nineteen and twenty hours a day, there are others - the common shrew and Ball's porpoise-that are said to sleep very little. There are also human beings who require only one to three hours of sleep a night. They take second and third jobs, putter around at night while their spouses sink into exhaustion, and otherwise seem to lead full, alert and constructive lives. Family histories suggest that these predispositions are hereditary. In one case, both a man and his little daughter are afflicted with this blessing or curse, much to the groggy consternation of his wife, who has since divorced him for a novel incompatibility. He retained custody of the daughter. Such examples suggest that the hypothesis of the recuperative function of sleep is at best not the whole story.

* The electroencephalograph (EEG) was invented by a German psychologist, Hans Berger, whose fundamental interest in the matter seems to have been telepathy. And, indeed, it can be used for a kind of radio telepathy; human beings have the capability to turn particular brain waves-for example, the alpha rhythm-on and off at will, although this feat requires a little training. With such training, an individual attached to an electroencephalograph and a radio transmitter could, in principle, send quite complex messages in a kind of alpha wave Morse code, merely by thinking them in the right way; and it is just possible that this method might have some practical use, such as permitting patients immobilized by severe stroke to communicate. For historical reasons, non-dreaming sleep is electroencephalographically characterized as "slow wave sleep," and the dream state as '-'paradoxical sleep."

Yet sleep is very ancient. In the electroencephalographic sense we share it with all the primates and almost all the other mammals and birds: it may extend back as far as the reptiles. Temporal-lobe epilepsy and its accompanying state of unconscious automatic behavior can be induced in some people by spontaneous electrical stimulation of the amygdala, deep below the temporal lobe, at frequencies of a few cycles per second (a few Hertz). Seizures not very different from sleep have been reported when an epileptic patient is driving in an automobile near sunset or sunrise with a picket fence between him and the sun: at a certain speed the pickets intercept the sun at just the critical rate to produce a flicker at the resonant frequency for initiating such seizures. The circadian rhythm, the daily cycling of physiological function, is known to go back at least to animals as humble as mollusks. Since a state in some respects resembling dreaming can be induced by electrical stimulation of other limbic regions below the temporal lobe, as described below, centers that initiate both sleep and dreams may not be far apart in the recesses of the brain.

There is some recent evidence that the two types of sleep, dreaming and dreamless, depend on the lifestyle of the animal. Truett Allison and Domenic Ciccheti of Yale University have found that predators are statistically much more likely to dream than prey, which are in turn much more likely to experience dreamless sleep. These studies are all of mammals and apply only to differences between, not within, species. In dream sleep, the animal is powerfully immobilized and remarkably unresponsive to external stimuli. Dreamless sleep is much shallower, and we have all witnessed cats or dogs cocking their ears to a sound when apparently fast asleep. It is also commonly held that when sleeping dogs move their legs in a kind of running pattern, they are dreaming of the hunt. The fact that deep dream sleep is rare among prey today seems clearly to be a product of natural selection. But organisms that are largely prey today may have had ancestors that were predators, and vice versa. Moreover, predators are generally organisms with larger absolute brain mass and ratio of brain to body mass than their prey. It makes sense that today, when sleep is highly evolved, the stupid animals are less frequently immobilized by deep sleep than the smart ones. But why should they sleep deeply at all? Why should a state of such deep immobilization ever have evolved?

Perhaps one useful hint about the original function of sleep is to be found in the fact that dolphins and whales and aquatic mammals in general seem to sleep very little. There is, by and large, no place to hide in the ocean. Could it be that, rather than increasing an animal's vulnerability, the function of sleep is to decrease it? Wilse Webb of the University of Florida and Ray Meddis of London University have suggested this to be the case. The sleeping style of each organism is exquisitely adapted to the ecology of the animal. It is conceivable that animals who are too stupid to be quiet on their own initiative are, during periods of high risk, immobilized by the implacable arm of sleep. The point seems particularly clear for the young of predatory animals; not only are baby tigers covered with a superbly effective protective coloration, they also sleep a great deal. This is an interesting notion and probably at least partly true. It does not explain everything. Why do lions, who have few natural enemies, sleep? This question is not a very damaging objection because lions may have evolved from animals that were not the king of beasts. Likewise, adolescent gorillas, who have little to fear, nevertheless construct nests each night-perhaps because they evolved from more vulnerable predecessors. Or perhaps, once, the ancestors of lions and gorillas feared still more formidable predators.

The immobilization hypothesis seems particularly apt in light of the evolution of mammals, who arose in an epoch dominated by hissing, thundering and altogether nightmarish reptiles. But nearly all reptiles are cold-blooded* and, except in the tropics, are forced into nocturnal immobility. Mammals are warm-blooded and able to function at night. The nontropical nocturnal ecological niches may have been almost un-tenanted in the Triassic Period, some two hundred million years ago. Indeed, Harry Jerison has suggested that the evolution of mammals was accompanied by the development of then extremely sophisticated (and now commonplace) versions of hearing and smell, senses for perceiving distances and objects at night; and that the limbic system evolved from the necessity of processing the rich array of data from these newly elaborated senses. (A great deal of the visual-information processing in reptiles is done not in the brain but in the retina; the optical processing apparatus in the neocortex was largely a later evolutionary development.)

* Robert Bakker, a paleontologist at Harvard University, suggests that at least some dinosaurs were significantly warm-blooded; even so, it seems likely that they were not as insensitive to diurnal temperature change as mammals are, and that they slowed down substantially at night.

Perhaps it was essential for the early mammals to be immobilized and hidden during the daylight hours that were ruled by predatory reptiles. I am picturing a late Mesozoic landscape in which the mammals sleep fitfully by day and the reptiles by night. But at night even humble carnivorous protomammals must have posed a real threat to the cold-immobilized reptiles, and particularly to their eggs.

Judged by their endocranial volumes (see figure on page 39), the dinosaurs were, compared to mammals, remarkably stupid. To take some "well-known" examples, Tyrannosaurus rex had a brain volume of about 200 cubic centimeters (cc); Brachiosaurus, 150 cc; Triceratops, 70 cc; Diplodocus, 50 cc; Stegosaurus, 30 cc. Not one approached a chimpanzee in absolute brain mass; Stegosaurus, which weighed two metric tons, was probably far more stupid than a rabbit. When the large body weights of the dinosaurs are taken into account, the smallness of their brains becomes even more striking: Tyrannosaurus weighed 8 metric tons; Diplodocus, 12; and Brachiosaurus, 87. The ratio of brain to body weight in Brachiosaurus was ten thousand times smaller than that of man. Just as sharks are the largest-brained fish for their body weight, the carnivorous dinosaurs such as Tyrannosaurus were relatively larger-brained than such herbivores as Diplodocus and Brachiosaurus. I am sure that Tyrannosaurus was an efficient and terrifying killing machine. But despite their awesome aspect, the dinosaurs look vulnerable to dedicated and intelligent adversaries-such as the early mammals.

Our Mesozoic scene has a curiously vampiric quality with the carnivorous reptiles hunting the smart sleeping mammals by day, and the carnivorous mammals hunting the stupid immobile reptiles by night. While the reptiles buried, their eggs, it is unlikely that they actively protected either eggs or young. There are very few accounts of such behavior even in contemporary reptiles, and it is difficult to picture Tyrannosaurus rex brooding on a clutch of eggs. For these reasons, the mammals may have won the primordial war of the vampires; at least some paleontologists believe that the demise of the dinosaurs was accelerated by nocturnal predation on reptilian eggs by the early mammals. Two chicken eggs* for breakfast may be all-at least on the surface-that is left of this ancient mammalian cuisine.

* In fact, the birds are almost certainly the principal living descendants of the dinosaurs.

The most intelligent of the dinosaurs by the criterion of brain to body mass are the Saurornithoides, whose brain mass was typically about 50 grams to a body mass of about 50 kilograms, placing them near the ostrich in the figure on page 40. Indeed, they resembled ostriches. It might be very illuminating to examine fossil endocasts of their braincases. They probably hunted small animals for food and used the four fingers of their handlike appendages for many different tasks.

They are interesting beasts to speculate about. If the dinosaurs had not all been mysteriously extinguished some sixty-five million years ago, would the Saurornithoides have continued to evolve into increasingly intelligent forms? Would they have learned to hunt large mammals collectively and thus perhaps have prevented the great proliferation of mammals that followed the end of the Mesozoic Age? If it had not been for the extinction of the dinosaurs, would the dominant life forms on

Earth today be descendants of Sauronithoides, writing and reading books, speculating on what would have happened had the mammals prevailed? Would the dominant forms think that base 8 arithmetic was quite natural, but base 10 a frill taught only in the "New Math"?

A great deal of what we consider important about the last few tens of millions of years of Earth's history seems to hinge on the extinction of the dinosaurs. There are literally dozens of scientific hypotheses that attempt to explain this event, which appears to have been remarkably rapid and thorough for both land and water forms. All the explanations proposed seem to be only partly satisfactory. They range from massive climatic change to mammalian predation to the extinction of a plant with apparent laxative properties, in which case the dinosaurs died of constipation.

One of the most interesting and promising hypotheses, first suggested by I. S. Shklovskii of the Institute for Cosmic Research, Soviet Academy of Sciences, Moscow, is that the dinosaurs died because of a nearby supernova event- the explosion of a dying star some tens of light-years away, which resulted in an immense flux of high energy charged particles that entered our atmosphere, changed its properties, and, perhaps by destroying the atmospheric ozone, let in lethal quantities of solar ultraviolet radiation. Nocturnal animals, such as the mammals of the time, and deep-sea animals, such as fish, could have survived this higher ultraviolet intensity; but daytime animals that lived on land or near the surface of the waters would have been preferentially destroyed. Such a disaster would be aptly named- the word itself means "bad star."

If this sequence of events is correct, the major course of biological evolution on the Earth in the last sixty-five million years, and indeed the very existence of human beings, can be traced to the death of a distant sun. Perhaps other planets circled that star; perhaps one of those planets enjoyed a thriving biology tortuously evolved over billions of years. The supernova explosion would surely have extinguished all life on that planet and probably even driven its atmosphere into space.

Do we owe our existence to a mighty stellar catastrophe that elsewhere destroyed biospheres and worlds?

After the extinction of the dinosaurs, mammals moved into daytime ecological niches. The primate fear of the dark must be a comparatively recent development. Washburn has reported that infant baboons and other young primates appear to be born with only three inborn fears-of falling, snakes, and the dark-corresponding respectively to the dangers posed by Newtonian gravitation to tree-dwellers, by our ancient enemies the reptiles, and by mammalian nocturnal predators, which must have been particularly terrifying for the visually oriented primates.

If the vampiric hypothesis is true-and it is at hest a likely hypothesis-the function of sleep is built deeply into the mammalian brain; from earliest mammalian times, sleep played a fundamental role in survival. Since for primitive mammals sleepless nights would have been more dangerous for the survival of the taxon than sexless nights, sleep should be a more powerful drive than sex-which, at least in most of us, it seems to be. But eventually mammals evolved to a point where sleep could be modified by changed circumstances. With the extinction of the dinosaurs, daylight suddenly became a benevolent environment for the mammals. Daytime immobilization was no longer compulsory, and a wide variety of sleep patterns slowly developed, including the contemporary correlation of mammalian predators with extensive dreaming and mammalian prey with a more watchful dreamless sleep. Perhaps those people who can do with only a few hours' sleep a night are the harbingers of a new human adaptation that will take full advantage of the twenty-four hours of the day. I, for one, freely confess envy for such an adaptation.

These conjectures on the origins of the mammals constitute a kind of scientific myth: they may have some germ of truth in them, but they are unlikely to be the whole story. That scientific myths make contact with more ancient myths may or may not be a coincidence. It is entirely possible that we are able to invent scientific myths only because we have previously been exposed to the other sort. Nevertheless, I cannot resist connecting this account of the origin of mammals with another curious aspect of the Genesis myth of the exile from Eden. Because it is a reptile, of course, that offers the fruit of the knowledge of good and-evil-abstract and moral neocortical functions-to Adam and Eve.

There are today a few remaining large reptiles on Earth, the most striking of which is the Komodo dragon of Indonesia: cold-blooded, not very bright, but a predator exhibiting a chilling fixity of purpose. With immense patience, it will stalk a sleeping deer or boar, then suddenly slash a hind leg and hang on until the prey bleeds to death. Prey is tracked by scent, and a hunting dragon lumbers and sashays, head down, its forked tongue flicking over the ground for chemical traces. The largest adults weigh about 135 kilograms (300 pounds), are three meters (about 10 feet) long and live perhaps to be centenarians. To protect its eggs, the dragon digs trenches from two to as much as nine meters (almost 30 feet) deep-probably a defense against egg-eating mammals (and themselves: Adults are known occasionally to stalk a nest-hole, waiting for the newly hatched young to emerge and provide a little delicacy for lunch). As another clear adaptation to predators, the dragon hatchlings live in trees.

The remarkable elaboration of these adaptations shows clearly that dragons are in trouble on the planet Earth. The Komodo dragon lives in the wild only in the Lesser Sunda Islands.* There are only about 2,000 of them left. The obscurity of their locale immediately suggests that dragons are near extinction because of mammalian, chiefly human, predation, a conclusion borne out by their history over the last two centuries. All dragons with less extreme adaptations or less remote habitats are dead. I even wonder whether the systematic separation of brain mass for a given body mass between mammals and reptiles (see chart on page 39) might not be the result of a systematic extinction of bright dragons by mammalian predators. In any case, it is very likely that the population of large reptiles has been declining steadily since the end of the Mesozoic Age, and that there were many more of them even one or two thousand years ago than there are today.

The pervasiveness of dragon myths in the folk legends of many cultures is probably no accident.+

* It is in the Greater Sunda Islands-more specifically Java- that the first specimen of Homo erectus, with an endocranial volume of almost 1,000 cc, was found by E. Dubok in 1891. + Curiously, the first representative skull of Pelting man- the Homo erectus whose remains are clearly associated with the use of fire.

The implacable mutual hostility between man and dragon, as exemplified in the myth of St. George, is strongest in the West. (In chapter 3 of the Book of Genesis, God ordains an eternal enmity between reptiles and humans.) But it is not a Western anomaly. It is a worldwide phenomenon. Is it only an accident that the common human sounds commanding silence or attracting attention seem strangely imitative of the hissing of reptiles? Is it possible that dragons posed a problem for our protohuman ancestors of a few million years ago, and that the terror they evoked and the deaths they caused helped bring about the evolution of human intelligence? Or does the metaphor of the serpent refer to the use of the aggressive and ritualistic reptilian component of our brain in the further evolution of the neocortex? With one exception, the Genesis account of the temptation by a reptile in Eden is the only instance in the Bible of humans understanding the language of animals. When we feared the dragons, were we fearing a part of ourselves? One way or another, there were dragons in Eden. in Sinkiang Province, China, in a place called the Mountain of Dragons.

The most recent dinosaur fossil is dated at about sixty million years ago. The family of man (but not the genus Homo) is some tens of millions of years old. Could there have been manlike creatures who actually encountered Tyrannosaurus rex? Could there have been dinosaurs that escaped the extinctions in the late Cretaceous Period? Could the pervasive dreams and common fears of "monsters," which children develop shortly after they are able to talk, be evolutionary vestiges of quite adaptive-baboonlike-responses to dragons and owls? *

* Since writing this passage I have discovered that Darwin expressed a similar thought: "May we not suspect that the vague but very real fears of children, which are quite independent of experience, are inherited effects of real dangers and abject superstitions during ancient savage times? It is quite conformable with what we know of the transmission of formerly well-developed characters, that they should appear at an early period of life, and afterwards disappear-like gill slits in human embryology."

What functions do dreams serve today? One view, published in a reputable scientific paper, holds that the function of dreams is to wake us up a little, every now and then, to see if anyone is about to eat us. But dreams occupy such a relatively small part of normal sleep that this explanation does not seem very compelling. Moreover, as we have seen, the evidence points just the other way: today it is the mammalian predators, not the mammalian prey, who characteristically have dream-filled sleep. Much more plausible is the computer-based explanation that dreams are a spillover from the unconscious processing of the day's experience, from the brain's decision on how much of the daily events temporarily stored in a kind of buffer to emplace in long-term memory. The events of yesterday frequently run through my dreams; the events of two days ago, much more rarely. However, the buffer-dumping model seems unlikely to be the whole story, because it does not explain the disguises that are so characteristic of the symbolic language of dreams, a point first stressed by Freud. It also does not explain the powerful affect or emotions of dreams; I believe there are many people who have been far more thoroughly frightened by their dreams than by anything they have ever experienced while awake.

The buffer-dumping and memory-storage functions of dreams have some interesting social implications. The American psychiatrist Ernest Hartmann of Tufts University has provided anecdotal but reasonably persuasive evidence that people who are engaged in intellectual activities during the day, especially unfamiliar intellectual activities, require more sleep at night, while, by and large, those engaged in mainly repetitive and intellectually unchallenging tasks are able to do with much less sleep. However, in part for reasons of organizational convenience, modern societies are structured as if all humans had the same sleep requirements; and in many parts of the world there is a satisfying sense of moral rectitude in rising early. The amount of sleep required for buffer dumping would then depend on how much we have both thought and experienced since the last sleep period. (There is no evidence that the causality runs backwards: people drugged with phenobarbital are not reported, during interstitial waking periods, to perform unusual intellectual accomplishments.) In this respect it would be interesting to examine individuals with very low sleep needs to determine whether the fraction of sleep time they spend dreaming is larger than it is for those with normal sleep requirements, and to determine whether their amount of sleep and dream time increases with the quality and quantity of their learning experiences while awake.

Michel Jouvet, a French neurologist at the University of Lyons, has found that dream sleep is triggered in the pons, which, while it resides in the hindbrain, is a late and essentially mammalian evolutionary development. On the other hand, Penfield has found that electrical stimulation deep into and below the temporal lobe in the neocortex and limbic complex can produce a waking state in epileptics very similar to that of dreams denuded of their symbolic and fantastic aspects. It can also induce the deja vu experience. Much of dream affect, including fear, can also be induced by-such electrical stimulation.

I once had a dream that will tantalize me forever. I dreamt I was idly thumbing through a thick history text. I could tell from the illustrations that the work was moving slowly, in the usual manner of such textbooks, through the centuries: classical times, Middle Ages, Renaissance and so on, gradually approaching the modern era. But then there was World War II with about two hundred pages left. With mounting excitement I

worked my way more deeply into the work until I was sure that I had passed my own time. It was a history book that included the future-like turning the December 31 page of the Cosmic Calendar and finding a fully detailed January 1. Breathlessly I attempted literally to read the future. But it was impossible. I could make out individual words. I could even discern the serifs on the individual characters. But I could not put the letters together into words or words' together into sentences. I was alexic.

Perhaps this is simply a metaphor of the unpredictability of the future. But my invariable dream experience is that I am unable to read, I can recognize, for example, a stop sign by its color and its octagonal shape, but I cannot read the word STOP, although I know it is there. I have the impression of understanding the meaning of a page of type, but not by reading it word by word or sentence by sentence. I cannot reliably perform even simple arithmetic operations in the dream state. I make a variety of verbal confusions of no apparent symbolic significance, like mixing up Schumann and Schubert. I am a little aphasic and entirely alexic. Not everyone I know has the same cognitive impairment in the dream state, but people often have some impairment. (Incidentally, individuals who are blind from birth have auditory, not visual dreams.) The neocortex is by no means altogether turned off in the dream state, but it certainly seems to suffer important malfunctions.

The seeming fact that mammals and birds both dream while their common ancestor, the reptiles, do not is surely noteworthy. Major evolution beyond the reptiles has been accompanied by and perhaps requires dreams. The electrically distinctive sleep of birds is episodic and brief. If they dream, they dream for only about a second at a time. But birds are, in an evolutionary sense, much closer to reptiles than mammals are. If we knew only about mammals, the argument would be more shaky; but when both major taxonomic groups that have evolved from the reptiles find themselves compelled to dream, we must take the coincidence seriously. Why should an animal that has evolved from a reptile have to dream while other animals do not? Could it be because the reptilian brain is still present and functioning?

It is extremely rare in the dream state that we bring ourselves up short and say, "This is only a dream." By and large we invest the dream content with reality. There are no rules of internal consistency that dreams are required to follow. The dream is a world of magic and ritual, passion and anger, but very rarely of skepticism and reason. In the metaphor of the triune brain, dreams are partially a function of the R-complex and the limbic cortex, but not of the rational part of the neocortex.

Experiments suggest that as the night wears on our dreams engage increasingly earlier material from our past, reaching back to childhood and infancy. At the same time the primary process and emotional content of the dream also increase. We are much more likely to dream of the passions of the cradle just before awakening than just after falling asleep. This looks very much as if the integration of the day's experience into our memory, the forging of new neural links, is either an easier or a more urgent task. As the night wears on and this function is completed, the more affecting dreams, the more bizarre material, the fears and lusts and other powerful emotions of the dream material emerge. Late at night, when it is very still and the obligatory daily dreams have been dreamt, the gazelles and the dragons begin to stir.

One of the most significant tools in studying the dream state was developed by William Dement, a Stanford University psychiatrist, who is as sane as it is possible for a human being to be, but who bears an exceedingly interesting name for a man of his profession. The dream state is accompanied by rapid eye movements (REM), which can be detected by electrodes taped lightly over the eyelids in sleep, and by a particular brain wave pattern on the EEG. Dement has found that everyone dreams many times each night. On awakening, an individual in the midst of REM sleep will usually remember his dream. Even people who claim never to dream have been discovered by REM and EEG criteria to dream as much as anyone else; and, when awakened at appropriate times, they admit with some surprise to having dreamt. The human brain is in a distinct physiological state while dreaming, and we dream rather often. While perhaps 20 percent of the subjects awakened during REM sleep do not recall their dreams, and some perhaps 10 percent of subjects awakened during non-REM sleep report dreams, we will, for convenience, identify REM and accompanying EEG patterns with the dream state.

There is some evidence that dreaming is necessary. When people or other mammals are deprived of REM sleep (by awakening them as soon as the characteristic REM and EEG dream patterns emerge), the number of initiations of the dream state per night goes up, and, in severe cases, daytime hallucinations-that is, waking dreams-occur. I have mentioned that the REM and EEC patterns of dreams are brief in birds and absent in reptiles. Dreams seem to be primarily a mammalian function. What is more, dream sleep is most vigorously engaged in by human beings in the early postnatal period. Aristotle stated quite positively that infants do not dream at all. On the contrary, we find they may be dreaming most of the time. Full-term newborn babies spend more than half their sleep time in the REM dream state. In infants born a few weeks premature, the dream time is three-quarters or more of the total sleep time. Earlier in its intrauterine existence, the fetus may be dreaming all the time. (Indeed, newborn kittens are observed to spend all of their sleep time in the REM stage.) Recapitulation would then suggest that dreaming is an evolutionarily early and basic mammalian function.

There is another connection between infancy and dreams: both are followed by amnesia. When we emerge from either state, we have great difficulty remembering what we have experienced. In both cases, I would suggest, the left hemisphere of the neocortex, which is responsible for analytic recollection, has been functioning ineffectively. An alternative explanation is that in both dreams and early childhood we experience a kind of traumatic amnesia: The experiences are too painful to remember. But many dreams we forget are very pleasant, and it is difficult to believe that infancy is that unpleasant. Also some children seem capable of remembering extremely early experiences. Memories of events late in the first year of life are not extremely rare, and there are possible examples of even earlier recollections. At age three, my son Nicholas was asked for the earliest event he could recall and replied in a hushed tone while staring into middle distance, "It was red, and I was very cold." He was born by Caesarean section. It is probably very unlikely, but I wonder whether this could just possibly be a true birth memory.

At any rate, I think it is much more likely that childhood and dream amnesia arise from the fact that in those states our mental lives are determined almost entirely by the R-complex, the limbic system and the right cerebral hemisphere. In earliest childhood, the neocortex is underdeveloped; in amnesia, it is impaired.

There is a striking correlation of penile or clitoral erection with REM sleep, even when the manifest dream content has no overt sexual aspects whatever. In primates, such erections are connected with sex (of course!), aggression and the maintenance of social hierarchies. I think that when we dream there is a part of us engaged in activities rather like those of the squirrel monkeys I saw in Paul MacLean's laboratory. The R-complex is functioning in the dreams of humans; the dragons can be heard, hissing and rasping, and the dinosaurs thunder still.

One excellent test of the merit of scientific ideas is their subsequent validation. A theory is put forward on fragmentary evidence, then an experiment is performed, the outcome of which the proposer of the theory could not know. If the experiment confirms the original idea, this is usually taken as strong support for the theory. Freud held that the great majority, perhaps all, of the "psychic energy" of our primary-process emotions and dream material is sexual in origin. The absolutely essential role of sexual interest in providing for the propagation of the species makes this idea neither as silly nor as depraved as it appeared to many of Freud's Victorian contemporaries. Carl Gustav Jung, for example, held that Freud had severely overstated the primacy of sex in the affairs of the unconscious. But now, three-quarters of a century later, experiments in the laboratories of Dement and other psychologists appear to support Freud. It would, I think, require a very dedicated puritanism to deny some connection between penile or clitoral erection and sex. It seems to follow that sex and dreams are not casually or incidentally connected but rather have deep and fundamental ties-although dreams certainly partake of ritual, aggressive and hierarchical material as well. Particularly considering the state of sexual repression in late-nineteenth-century Viennese society, many of Freud's insights seem hard-won and courageous as well as valid.

Statistical studies have been made of the most common categories of dreams-studies which, at least to some extent, ought to illuminate the nature of dreams. In a survey of the dreams of college students, the following were, in order, the five most frequent types: (1) falling; (2) being pursued or attacked; (3) attempting repeatedly and unsuccessfully to perform a task; (4) various academic learning experiences; and (5) diverse sexual experiences. Number (4) on this list seems of special and particular concern to the group being sampled. The others, while sometimes actually encountered in the lives of undergraduates, are likely to be applicable generally, even to non-students.

The fear of falling seems clearly connected with our arboreal origins and is a fear we apparently share with other primates. If you live in a tree, the easiest way to die is simply to forget the danger of falling. The other three categories of most common dreams are particularly interesting because they correspond to aggressive, hierarchical, ritualistic and sexual functions -the realm of the R-complex. Another provocative statistic is that almost half of the people queried reported dreams about snakes, the only nonhuman animal rating a category all to itself in the twenty most common dreams. It is, of course, possible that many snake dreams have a straightforward Freudian interpretation. However, two-thirds of the respondents reported explicitly sexual dreams. Since, according to Wash-burn, young primates exhibit an untaught fear of snakes, it is easy to wonder whether the dream world does not point directly as well as indirectly to the ancient hostility between reptiles and mammals.

There is one hypothesis that seems to me consistent with all the foregoing facts: The evolution of the limbic system involved a radically new way of viewing the world. The survival of the early mammals depended on intelligence, daytime unobtrusiveness, and devotion to the young. The world as perceived through the R-complex was quite a different world. Because of the accretionary nature of the evolution of the brain, R-complex functions could be utilized or partially bypassed but not ignored. Thus, an inhibition center developed below what in humans is the temporal lobe, to turn off much of the functioning of the reptilian brain; and an activation center evolved in the pons to turn on the R-complex, but harmlessly, during sleep. This view, of course, has some notable points of similarity to Freud's picture of the repression of the id by the superego (or of the unconscious by the conscious), with expressions of the id made most clearly manifest in slips of the tongue, free associations, dreams and the like-that is, during the interstices of superego repression.

With the large-scale development of the neocortex in higher mammals and primates, some neocortical involvement in the dream state developed-a symbolic language is, after all, still a language. (This is related to the different functions of the two hemispheres of the neocortex, described in the following chapter.) But the dream imagery contained significant sexual, aggressive, hierarchical and ritualistic elements. The fantastic material in the dream world may be connected with the near-absence of direct sensory stimulation during dreams. There is very little reality testing in the dream state. The prevalence of dreams in infants would, in this view, be because, in infancy, the

There is one hypothesis that seems to me consistent with all the foregoing facts: The evolution of the limbic system involved a radically new way of viewing the world. The survival of the early mammals depended on intelligence, daytime unobtrusiveness, and devotion to the young. The world as perceived through the R-complex was quite a different world. Because of the accretionary nature of the evolution of the brain, R-complex functions could be utilized or partially bypassed but not ignored. Thus, an inhibition center developed below what in humans is the temporal lobe, to turn off much of the functioning of the reptilian brain; and an activation center evolved in the pons to turn on the R-complex, but harmlessly, during sleep. Tins view, of course, has some notable points of similarity to-Freud's picture of the repression of the id by the superego (or of the unconscious by the conscious), with expressions of the id made most clearly manifest in slips of the tongue, free associations, dreams and the like-that is, during the interstices of superego repression.

With the large-scale development of the neocortex in higher mammals and primates, some neocortical involvement in the dream state developed-a symbolic language is, after all, still a language. (This is related to the different functions of the two hemispheres of the neocortex, described in the following chapter.) But the dream imagery contained significant sexual, aggressive, hierarchical and ritualistic elements, fantastic material in the dream world may be connected with the near-absence of direct sensory stimulation during dreams. There is very little reality testing in the dream state. The prevalence of dreams in infants would, in this view, be because, in infancy, the analytic part of the neocortex is barely working. The absence of dreams in reptiles would be because there is no repression of the dream state in reptiles; they are, as Aeschylus described our ancestors, "dreaming" in their waking state. I believe this idea can explain the strangeness-that is, the differences from our waking verbal consciousness-of the dream state; its mammalian and human neonatal localization; its physiology; and its pervasiveness in man. We are descended from reptiles and mammals both. In the daytime repression of the R-complex and in the nighttime stirring of the dream dragons, we may each of us be replaying the hundred-million-year-old warfare between the reptiles and the mammals. Only the times of day of the vampiric hunt have been reversed.

Human beings exhibit enough reptilian behavior as it is. If we gave full rein to the reptilian aspects of our nature, we would clearly have a low survival potential. Because the R-complex is woven so intimately into the fabric of the brain, its functions cannot be entirely avoided for long. Perhaps the dream state permits, in our fantasy and its reality, the R-complex to function regularly, as if it were still in control. If this is true, I wonder, after Aeschylus, if the waking state of other mammals is very much like the dream state of humans-where we can recognize signs, such as the feeling of running water and the smell of honeysuckle, but have an extremely limited repertoire of symbols such as words; where we encounter vivid sensory and emotional images and active intuitive understanding, but very little rational analysis; where we are unable to perform tasks requiring extensive concentration; where we experience short attention spans and frequent distractions and, most of all, a very feeble sense of individuality or self, which gives way to a pervading fatalism, a sense of unpredictable buffeting by uncontrollable events. If this is where we have come from, we have come very far.

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