Lovers and madmen have such seething brains Such shaping fantasies, that apprehend More than cool reason ever comprehends. The lunatic, the lover, and the poet Are of imagination all compact...
A Midsummer Night’s Dream

Mere poets are as sottish as mere drunkards are, who live in a continual mist, without seeing or judging anything clearly.
A man should be learned in several sciences,
and should have a reasonable, philosophical,
and in some measure a mathematical head,
to be a complete and excellent poet. . .

“Notes and Observations on The Empress of Morocco,” 1674

BLOODHOUNDS have a widely celebrated ability to track by smell. They are presented with a “trace”-a scrap of clothing belonging to the target, the lost child or the escaped convict-and then, barking, bound joyously and accurately down the trail. Canines and many other hunting animals have such ability in extremely well developed form. The original trace contains an olfactory cue, a smell. A smell is merely the perception of a particular variety of molecule-in this case, an organic molecule.


For the bloodhound to track, it must be able to sense the difference in smell -in characteristic body molecules-between the target and a bewildering and noisy background of other molecules, some from other humans who have gone the same way (including those organizing the tracking expedition) and some from other animals (including the dog itself). The number of molecules shed by a human being while walking is relatively small. Yet even on a fairly “cold” trail-say, several hours after the disappearance-bloodhounds can track successfully.


This remarkable ability involves extremely sensitive olfactory detection, a function, as we saw earlier, performed well even by insects. But what is most striking about the bloodhound and different from insects is the richness of its discriminative ability, its aptitude in distinguishing among many different smells, each in an immense background of other odors. The bloodhound performs a sophisticated cataloging of molecular structure; it distinguishes the new molecule from a very large library of other molecules previously smelled. What is more, the bloodhound needs only a minute or less to familiarize itself to the smell, which it can then remember for extensive periods of time.

The olfactory recognition of individual molecules is apparently accomplished by individual nasal receptors sensitive to particular functional groups, or parts, of organic molecules. One receptor, for example, may be sensitive to COOH, another to NH2, and so on. (C stands for carbon. H for hydrogen, O for oxygen and N for nitrogen.) The various appurtenances and projections of the complex molecules apparently adhere to different molecular receptors in the nasal mucosa, and the detectors for all the functional groups combine to put together a kind of collective olfactory image of the molecule. This is an extremely sophisticated sensory system.


The most elaborate man-made device of this sort, the gas chromatograph/mass spectrometer, has in general neither the sensitivity nor the discriminative ability of the bloodhound, although substantial progress is being made in this technology. The olfactory system of animals has evolved into its present sophistication because of strong selection pressures. Early detection of mates, predators and prey is a matter of life and death for the species.


The sense of smell is very ancient, and indeed, much of the early evolution above the level of the neural chassis may have been spurred by selection pressure for such molecular detection: the distinctive olfactory bulbs in the brain (see figure on page 55) are among the first components of the neocortex to have developed in the history of life. Indeed, the limbic system was called the “rhinencephalon,” the smell-brain, by Herrick.

The sense of smell is not nearly so well developed in humans as in bloodhounds. Despite the massive-ness of our brains, our olfactory bulbs are smaller than those of many other animals, and it is clear that smell plays a very minor role in our everyday lives. The average person is able to distinguish relatively few smells. Our verbal descriptions and analytic comprehension of smell, even with only a few odors in our repertoire, is extremely poor. Our response to an odor hardly resembles, in our own perception, the actual three-dimensional structure of the molecule responsible for the smell. Olfaction is a complex cognitive task which we can, within limits, perform-and with considerable accuracy-but which we can describe inadequately at best. And if the bloodhound could speak, I think it would be at a similar loss to describe the details of what it does so supremely well.

Just as smell is the principal means by which dogs and many other animals perceive their surroundings, sight is the primary information channel in humans. We are capable of visual sensitivity and discrimination at least as impressive as the olfactory abilities of the bloodhound. For example, we are able to discriminate among faces. Careful observers can distinguish among tens or even hundreds of thousands of different faces; and the “Identikit,” widely used by Interpol and by police forces in the West generally, is capable of reconstructing more than ten billion different faces. The survival value of such an ability, particularly for our ancestors, is quite clear.


Yet consider how incapable we are of describing verbally faces that we are perfectly capable of recognizing. Witnesses commonly exhibit a total failure in verbal description of an individual previously encountered, but high accuracy in recognizing the same individual when seen again. And while cases of mistaken identity have certainly occurred, courts of law seem willing to admit the testimony of any adult witness on questions of facial recognition. Consider how easily we can pick, from a vast crowd of faces, a “celebrity”; or how in a dense non-ordered list our own name leaps out at us.

Human beings and other animals have very sophisticated high-data-rate perceptual and cognitive abilities that simply bypass the verbal and analytic consciousness that so many of us regard as all of us there is. This other kind of knowing, our nonverbal perceptions and cognitions, is often described as “intuitive.” The word does not mean “innate.” No one is born with a repertoire of faces implanted in his brain. The word conveys, I think, a diffuse annoyance at our inability to understand how we come by such knowledge. But intuitive knowledge has an extremely long evolutionary history; if we consider the information contained in the genetic material, it goes back to the origin of life.


The other of our two modes of knowing-the one that in the West expresses irritation about the existence of intuitive knowledge-is a quite recent evolutionary accretion. Rational thinking that is fully verbal (involving complete sentences, say) is probably only tens or hundreds of thousands of years old. There are many people who are, in their conscious lives, almost entirely rational, and many who are almost entirely intuitive. Each group, with very little appreciation of the reciprocal value of these two kinds of cognitive ability, derides the other: “muddled” and “amoral” are typical adjectives used in the more polite of such exchanges.

Why should we have two different, accurate and complementary modes of thinking which are so poorly integrated with each other?

The first evidence that these two modes of thinking are localized in the cerebral cortex has come from the study of brain lesions. Accidents or strokes in the temporal or parietal lobes of the left hemisphere of the neocortex characteristically result in impairment of the ability to read, write, speak and do arithmetic. Comparable lesions in the right hemisphere lead to impairment of three-dimensional vision, pattern recognition, musical ability and holistic reasoning.


Facial recognition resides preferentially in the right hemisphere, and those who “never forget a face” are performing pattern recognition on the right side. Injuries to the right parietal lobe, in fact, sometimes results in the inability of a patient to recognize his own face in a mirror or photograph. Such observations strongly suggest that those functions we describe as “rational” live mainly in the left hemisphere, and those we consider “intuitive,” mainly in the right.

The most significant recent experiments along these lines have been performed by Roger Sperry and his collaborators at the California Institute of Technology. In an attempt to treat severe cases of grand mal epilepsy, where patients suffer from virtually continuous seizures (as frequent as twice an hour, forever), they cut the corpus callosum, the main bundle of neural fibers connecting the left and right hemispheres of the neocortex (see the figure on page 167).


The operation was an effort to prevent a kind of neuroelectrical storm in one hemisphere from propagating, far from its focus, into the other. The hope was that at least one of the two postoperative hemispheres would be unaffected by subsequent seizures. The unexpected and welcome result was that the frequency and intensity of the seizures declined dramatically in both hemispheres-as if there had previously been a positive feedback, with the epileptic electrical activity in each hemisphere stimulating the other through the corpus callosum.

Such “split-brain” patients appear, superficially, entirely normal after the surgery. Some report a complete cessation of the vivid dreams they experienced before the operation. The first such patient was unable to speak for a month after the operation, but his aphasia later disappeared. The normal behavior and appearance of split-brain patients in itself suggests that the function of the corpus callosum is subtle. Here is a bundle of two hundred million neural fibers processing something like several billion bits per second between the two cerebral hemispheres. It contains about 2 percent of the total number of neurons in the neocortex. And yet when it is cut, nothing seems to change. I think it is obvious that there must in fact be significant changes, but ones that require a deeper scrutiny.

When we examine an object to our right, both eyes are viewing what is called the right visual field; and to our left, the left visual field. But because of the way the optic nerves are connected, the right visual field is processed in the left hemisphere and the left visual field in the right hemisphere. Likewise, sounds from the right ear are processed primarily in the left hemisphere of the brain and vice versa, although there is some audio processing on the same side-for example, sounds from the left ear in the left hemisphere.


No such crossing of function occurs in the more primitive sense of smell, and an odor detected by the left nostril only is processed exclusively in the left hemisphere. But information sent between the brain and the limbs is crossed. Objects felt by the left hand are perceived primarily in the right hemisphere, and instructions to the right hand to write a sentence are processed in the left hemisphere. In 90 percent of human subjects, the centers for speech are in the left hemisphere.

Sperry and his collaborators have performed an elegant series of experiments in which separate stimuli are presented to the left and right hemispheres of split-brain patients. In a typical experiment, the word hatband is flashed on a screen-but hat is in the left visual field and band in the right visual field. The patient reports that he saw the word band, and it is clear that, at least in terms of his ability to communicate verbally, he has no idea that the right hemisphere received a visual impression of the word hat.


When asked what kind of band it was, the patient might guess: outlaw band, rubber band, jazz band. But when, in comparable experiments, the patient is asked to write what he saw, but with his left hand inside a box, he scrawls the word hat. He knows from the motion of his hand that he has written something, but because he cannot see it, there is no way for the information to arrive in the left hemisphere which controls verbal ability. Bewilderingly, he can write, but cannot utter, the answer.

Many other experiments exhibit similar results. In one, the patient is able to feel three-dimensional plastic letters which are out of view with his left hand. The available letters can spell only one correct English word, such as love or cup, which the patient is able to work out: the right hemisphere has a weak verbal ability, roughly comparable to that in dreams. But after correctly spelling the word, the patient is unable to give any verbal indication of what word he has spelled. It seems clear that in split-brain patients, each hemisphere has scarcely the faintest idea what the other hemisphere has learned.

The geometrical incompetence of the left hemisphere is impressive; it is depicted by the illustration on the opposite page: A right-handed split-brain patient was able to copy simple representations of three-dimensional figures accurately only with his (inexperienced) left hand. The right hemisphere’s superiority at geometry seems restricted to manipulative tasks; this dominance does not hold for other sorts of geometrical functions that do not require hand-eye-brain coordination.


These manipulative geometrical activities seem to be localized in the right hemisphere’s parietal lobe, in a place that, in the left hemisphere, is devoted to language. M. S. Gazzaniga of the State University of New York at Stony Brook suggests that this hemispheric specialization occurs because language is developed in the left hemisphere before the child acquires substantial competence in manipulative skills and geometrical visualization. According to this view, the specialization of the right hemisphere for geometrical competence is a specialization by default-the left hemisphere’s competence has been redirected toward language.

Shortly after one of Sperry’s most convincing experiments had been completed, he gave a party, so the story goes, to which a famous theoretical physicist with an intact corpus callosum was invited. The physicist, known for his lively sense of humor, sat quietly through the party, listening with interest to Sperry’s description of the split-brain findings. The evening passed, the guests trickled away, and Sperry found, himself at the door bidding goodbye to the last of them. The physicist extended his right hand, shook Sperry’s and told him what a fascinating evening he had had. Then, with a little two-step, he changed the positions of his right and left feet, extended his left hand, and said in a strangled, high-pitched voice, “And I want you to know I had a terrific time too.”

When communication between the two cerebral hemispheres is impaired, the patient often finds his own behavior inexplicable, and it is clear that even in “good speaking” the speaker may not know “the truth of the matter.” (Compare with the remark on page 2, from the Phaedrus.) The relative independence of the two hemispheres is apparent in everyday life. We have already mentioned the difficulty of describing verbally the complex perceptions of the right hemisphere. Many elaborate physical tasks, including athletics, seem to have relatively little left-hemisphere involvement.


A well-known “ploy” in tennis, for example, is to ask your opponent exactly where on the racket he places his thumb. It often happens that left-hemisphere attention to this question will, at least for a brief period, destroy his game. A great deal of musical ability is a right-hemisphere function. It is a commonplace that we may memorize a song or a piece of music without having the least ability to write it down in musical notation. In piano, we might describe this by saying that our fingers (but not we) have memorized the piece.

Such memorization can be quite complex. I recently had the pleasure of witnessing the rehearsal of a new piano concerto by a major symphony orchestra. In such rehearsals the conductor does not often start from the beginning and run through to the end. Rather, because of the expense of rehearsal time as well as the competence of the performers, he concentrates on the difficult passages. I was impressed that not only had the soloist memorized the entire piece, she was also able to begin at any requested place in the composition after only a brief glance at the designated measure in the score. This enviable skill is a mixed left and right hemisphere function. It is remarkably difficult to memorize a piece of music you have never heard so that you are able to intervene in any measure. In computer terminology, the pianist had random access as opposed to serial access to the composition.

This is a good example of the cooperation between left and right hemispheres in many of the most difficult and highly valued human activities. It is vital not to overestimate the separation of functions on either side of the corpus callosum in a normal human being. The existence of so complex a cabling system as the corpus callosum must mean, it is important to stress again, that interaction of the hemispheres is a vital human function.

In addition to the corpus callosum there is another neural cabling between the left and right hemispheres, which is called the anterior commissure. It is much smaller than the corpus callosum (see figure on page 167), and exists, as the corpus callosum does not, in the brain of the fish. In human split-brain experiments in which the corpus callosum is cut, but not the anterior commissure, olfactory information is invariably transferred between the hemispheres.


Occasional transfer of some visual and auditory information through the anterior commissure also seems to occur, but un-predictably from patient to patient. These findings are consistent with anatomy and evolution; the anterior commissure (and the hippocampal commissure; see the figure on p. 167) lies deeper than the corpus callosum and transfers information in the limbic cortex and perhaps in other more ancient components of the brain.

Humans exhibit an interesting separation of musical and verbal skills. Patients with lesions of the right temporal lobe or right hemispherectomies are significantly impaired in musical but not in verbal ability- in particular in the recognition and recall of melodies. But their ability to read music is unimpaired. This seems perfectly consistent with the separation of functions described: the memorization and appreciation of music involves the recognition of auditory patterns and a holistic rather than analytic temperament. There is some evidence that poetry is partly a right-hemisphere function; in some cases the patient begins to write poetry for the first time in his life after a lesion in the left hemisphere has left him aphasic. But this would perhaps be, in Dryden’s words, “mere poetry.” Also, the right hemisphere is apparently unable to rhyme.

The separation or lateralization of cortical function was discovered by experiments on brain-damaged individuals. It is, however, important to demonstrate that the conclusions apply to normal humans. Experiments carried out by Gazzaniga present brain-undamaged individuals with a word half in the left and half in the right visual fields, as in split-brain patients, and the reconstruction of the word is monitored.


The results indicate that, in the normal brain, the right hemisphere does very little processing of language but instead transmits what it has observed across the corpus callosum to the left hemisphere, where the entire word is put together. Gazzaniga also found a split-brain patient whose right hemisphere was astonishingly competent in language skills: but this patient had experienced a brain pathology in the temporal-parietal region of the left hemisphere at an early age. We have already mentioned the ability of the brain to relocalize functions after injury in the first two years of life, but not thereafter.

Robert Ornstein and David Galin of the Langley Porter Neuropsychiatric Institute in San Francisco claim that as normal people change from analytic to synthetic intellectual activities the EEG activity of the corresponding cerebral hemispheres varies in the predicted way: when a subject is performing mental arithmetic, for example, the right hemisphere exhibits the alpha rhythm characteristic of an “idling” cerebral hemisphere. If this result is confirmed, it would be quite an important finding.

Ornstein offers an interesting analogy to explain why, in the West at least, we have made so much contact with left-hemisphere functions and so little with right. He suggests that our awareness of right hemisphere function is a little like our ability to see stars in the daytime. The sun is so bright that the stars are invisible, despite the fact that they are just as present in our sky in the daytime as at night. When the sun sets, we are able to perceive the stars. In the same way, the brilliance of our most recent evolutionary accretion, the verbal abilities of the left hemisphere, obscures our awareness of the functions of the intuitive right hemisphere, which in our ancestors must have been the principal means of perceiving the world.*


* Marijuana is often described as improving our appreciation of and abilities in music, dance, art, pattern and sign recognition and our sensitivity to nonverbal communication. To the best of my knowledge, it is never reported as improving our ability to read and comprehend Ludwig Wittgenstein or Immanuel Kant; to calculate the stresses on bridges; or to compute Laplace transformations. Often the subject has difficulty even in writing down his thoughts coherently. I wonder if, rather than enhancing anything, the cannabinols (the active ingredients in marijuana) simply suppress the left hemisphere and permit the stars to come out. This may also be the objective of the meditative states of many Oriental religions.

The left hemisphere processes information sequentially; the right hemisphere simultaneously, accessing several inputs at once. The left hemisphere works in series; the right in parallel. The left hemisphere is something like a digital computer; the right like an analog computer. Sperry suggested that the separation of function in the two hemispheres is the consequence of a “basic incompatibility.” Perhaps we are today able to sense directly the operations of the right hemisphere mainly when the left hemisphere has “set”-that is, in dreams.

In the previous chapter, I proposed that a major aspect of the dream state might be the unleashing, at night, of R-complex processes that had been largely repressed by the neocortex during the day. But I mentioned that the important symbolic content of dreams showed significant neocortical involvement, although the frequently reported impairments in reading, writing, arithmetic and verbal recall suffered in dreams were striking.

In addition to the symbolic content of dreams, other aspects of dream imagery point to a neocortical presence in the dream process. For example, I have many times experienced dreams in which the denouement or critical “plot surprise” was possible only because of clues-apparently unimportant-inserted much earlier into the dream content. The entire plot development of the dream must have been in my mind at the time the dream began. (Incidentally, the time taken for dream events has been shown by Dement to be approximately equal to the time the same events would have taken in real life.) While the content of many dreams seems haphazard, others are remarkably well structured; these dreams have a remarkable resemblance to drama.

We now recognize the very attractive possibility that the left hemisphere of the neocortex is suppressed in the dream state, while the right hemisphere-which has an extensive familiarity with signs but only a halt-ting verbal literacy-is functioning well. It may be that the left hemisphere is not entirely turned off at night but instead is performing tasks that make it inaccessible to consciousness: it is busily engaged in data dumping from the short-term memory buffer, determining what should survive into long-term storage.

There are occasional but reliably reported instances of difficult intellectual problems solved during sleep. Perhaps the most famous is the dream of the German chemist Friedrich Kekule von Stradonitz. In 1865 the most pressing and puzzling problem in organic structural chemistry was the nature of the benzene molecule. The structure of several simple organic molecules had been deduced from their properties, and all were linear, the constituent atoms being attached to each other in a straight line. According to his own account, Kekule was dozing on a horse-drawn tram when he had a kind of dream of dancing atoms in linear arrangements.


Abruptly the tail of a chain of atoms attached itself to the head and formed a slowly rotating ring. On awakening and recalling this dream fragment, Kekule realized instantly that the solution to the benzene problem was a hexagonal ring of carbon atoms rather than a straight chain. Observe, however, that this is quintessentially a pattern-recognition exercise and not an analytic activity. It is typical of almost all of the famous creative acts accomplished in the dream state: they are right-hemisphere and not left-hemisphere activities.

The American psychoanalyst Erich Fromm has written:

“Must we not expect that, when deprived of the outside world, we regress temporarily to a primitive animal-like unreasonable state of mind? Much can be said in favor of such an assumption, and the view that such a regression is the essential feature of the state of sleep, and thus of dream activity, has been held by many students of dreaming from Plato to Freud.”

Fromm goes on to point out that we sometimes achieve in the dream state insights that have evaded us when awake.


But I believe these insights always have an intuitive or pattern-recognition character. The “animal-like” aspect of the dream state can be understood as the activities of the R-complex and the limbic system, and the occasionally blazing intuitive insight as the activity of the right hemisphere of the neocortex. Both cases occur because in each the repressive functions of the left hemisphere are turned off. These right-hemisphere insights Fromm calls “the forgotten language” - and he plausibly argues that they are the common origin of dreams, fairy tales and myths.

In dreams we are sometimes aware that a small portion of us is placidly watching; often, off in a corner of the dream, there is a kind of observer. It is this “watcher” part of our minds that occasionally - sometimes in the midst of a nightmare - will say to us, “This is only a dream.” It is the “watcher” who appreciates the dramatic unity of a finely structured dream plot. Most of the time, however, the “watcher” is entirely silent. In psychedelic drug experiences-for example, with marijuana or LSD-the presence of such a “watcher” is commonly reported. LSD experiences may be terrifying in the extreme, and several people have told me that the difference between sanity and insanity in the LSD experience rests entirely on the continued presence of the “watcher,” a small, silent portion of the waking consciousness.

In one marijuana experience, my informant became aware of the presence and, in a strange way, the in-appropriateness of this silent “watcher,” who responds with interest and occasional critical comment to the kaleidoscopic dream imagery of the marijuana experience but is not part of it. “Who are you?” my informant silently asked it. “Who wants to know?” it replied, making the experience very like a Sufi or Zen parable. But my informant’s question is a deep one. I would suggest the observer is a small part of the critical faculties of the left hemisphere, functioning much more in psychedelic than in dream experiences, but present to a degree in both. However, the ancient query, “Who is it who asks the question?” is still unanswered; perhaps it is another component of the left cerebral hemisphere.

An asymmetry in the temporal lobes in left and right hemispheres of humans and of chimpanzees has been found, with one portion of the left lobe significantly more developed.

Human infants are born with this asymmetry (which develops as early as the twenty-ninth week of gestation), thus suggesting a strong genetic predisposition to control speech in the left temporal lobe. (Nevertheless, children with lesions in the left temporal lobe are able, in their first year or two of life, to develop all speech functions in the comparable portion of the
right hemisphere with no impairment. At a later age, this replacement is impossible.) Also, lateralization is found in the behavior of young children. They are better able to understand verbal material with the right ear and nonverbal material with
the left, a regularity also found in adults.


Similarly, infants spend more time on the average looking at objects on their right than at identical objects on their left, and require a louder noise in the left ear than in the right to elicit a response. While no clear asymmetry of these sorts has yet been found in the brains or behavior of apes, Dewson’s results (see page 123) suggest that some lateralization may exist in the higher primates; there is no evidence for anatomical asymmetries in the temporal lobes of, say, rhesus monkeys. One would certainly guess that the linguistic abilities of chimpanzees are governed, as in humans, in the left temporal lobe.

The limited inventory of symbolic cries among non-human primates seems to be controlled by the limbic system; at least the full vocal repertoire of squirrel and rhesus monkeys can be evoked by electrical stimulation in the limbic system. Human language is controlled in the neocortex. Thus an essential step in human evolution must have been the transfer of control of vocal language from the limbic system to the temporal lobes of the neocortex, a transition from instinctual to learned communication.


However, the surprising ability of apes to acquire gestural language and the hint of lateralization in the chimpanzee brain suggest that the acquisition of voluntary symbolic language by-primates is not a recent invention. Rather, it goes back many millions of years, consistent with the evidence from endocranial casts for Broca’s area in Homo habilis. Lesions in the monkey brain of the neocortical areas responsible for speech in humans fail to impair their instinctual vocalizations.


The development of human language must therefore involve an essentially new brain system and not merely a reworking of the machinery for limbic cries and calls. Some experts in human evolution have suggested that the acquisition of language occurred very late-perhaps only in the last few tens of thousands of years-and was connected with the challenges of the last ice age. But the data do not seem to be consistent with this view; moreover, the speech centers of the human brain are so complex that it is very difficult to imagine their evolution in the thousand or so generations since the peak of the most recent glaciation.

The evidence suggests that in our ancestors of some tens of millions of years ago there was a neocortex, but one in which the left and right hemispheres served comparable and redundant functions. Since then, upright posture, the use of tools, and the development of language have mutually advanced one another, a small increment in language ability, for example, permitting the incremental improvement of hand axes, and vice versa. The corresponding brain evolution seems to have proceeded by specializing one of the two hemispheres for analytic thinking.

The original redundancy, by the way, represents prudent computer design. For example, with no knowledge of the neuroanatomy of the cerebral cortex, the engineers who designed the on-board memory of the Viking lander inserted two identical computers, which are identically programmed. But because of their complexity, differences between the computers soon emerged. Before landing on Mars the computers were given an intelligence test (by a smarter computer back on Earth). The dumber brain was then turned off.


Perhaps “human evolution has proceeded in a similar manner and our highly prized rational and analytical abilities are localized in the “other” brain-the one that was not fully competent to do intuitive thinking. Evolution often uses this strategy. Indeed, the standard evolutionary practice of increasing the amount of genetic information as organisms increase in complexity is accomplished by doubling part of the genetic material and then allowing the slow specialization of function of the redundant set.

Almost without exception all human languages have built into them a polarity, a veer to the right. “Right” is associated with legality, correct behavior, high moral principles, firmness, and masculinity; “left,” with weakness, cowardice, diffuseness of purpose, evil, and femininity. In English, for example, we have “rectitude,” “rectify,” “righteous,” “right-hand man,” “dexterity,” “adroit” (from the French “a droite”), “rights,” as in “the rights of man,” and the phrase “in his right mind.” Even “ambidextrous” means, ultimately, two right hands.

On the other side (literally), we have “sinister” (almost exactly the Latin word for “left”), “gauche” (precisely the French word for “left”), “gawky,” “gawk,” and “left-handed compliment.” The Russian “nalevo” for “left” also means “surreptitious.” The Italian “mancino” for “left” signifies “deceitful.” There is no “Bill of Lefts.”

In one etymology, “left” comes from “lyft,” the Anglo-Saxon for weak or worthless. “Right” in the legal sense (as an action in accord with the rules of society) and “right” in the logical sense (as the opposite of erroneous) are also commonplaces in many languages. The political use of right and left seems to date from the moment when a significant lay political force arose as counterpoise to the nobility. The nobles were placed on the king’s right and the radical upstarts -the capitalists-on his left. The nobles were to the royal right, of course, because the king himself was a noble; and his right side was the favored position. And in theology as in politics: “At the right hand of God.”

Many examples of a connection between “right” and “straight” can be found.* In Mexican Spanish you indicate straight (ahead) by saying “right right”; in Black American English, “right on” is an expression of approval, often for a sentiment eloquently or deftly-phrased. “Straight” meaning conventional, correct or proper is a commonplace in colloquial English today. In Russian, right is “/bravo,” a cognate of “pravda,” which means “true.” And in many languages “true” has the additional meaning of “straight” or “accurate,” as in “his aim was true.”


* I wonder if there is any significance to the fact that Latin, Germanic and Slavic languages, for example, are written left to right, and Semitic languages, right to left. The ancient Greeks wrote in boustrophedon (“as the ox plows”); left to right on one line, right to left on the next.

The Stanford-Binet IQ test makes some effort to examine both left- and right-hemisphere function. For right-hemisphere function there are tests in which the subject is asked to predict the opened configuration of a piece of paper after it is folded several times and a small piece cut out with a pair of scissors; or to estimate the total number of blocks in a stack when some blocks are hidden from view.


Although the devisers of the Stanford-Binet test consider such questions of geometric conception to be very useful in determining the “intelligence” of children, they are said to be increasingly less useful in IQ tests of teenagers and adults. There is certainly little room on such examinations for testing intuitive leaps. Unsurprisingly, IQ tests also seem to be powerfully biased toward the left hemisphere.

The vehemence of the prejudices in favor of the left hemisphere and the right hand reminds me of a war in which the side that barely won renames the contending parties and issues, so that future generations will have no difficulty in deciding where prudent loyalty should lie. When Lenin’s party was a fairly small splinter group in Russian socialism he named it the Bolshevik party, which in Russian means the majority party.


The opposition obligingly, and with awesome stupidity, accepted the designation of Mensheviks, the minority party. In a decade and a half they were. Similarly, in the worldwide associations of the words “right” and “left” there is evidence of a rancorous conflict early in the history of mankind.* What could arouse such powerful emotions?


* A quite different set of circumstances is revealed by another pair of verbal polar opposites: black and white. Despite English phrases of the sort “as different as black and white,” the two words appear to have the same origin. Black comes from the Anglo-Saxon “blaece,” and white from the Anglo-Saxon “blac,” which is still active in its cognates “blanch,” “blank,” “bleak,” and the French “blanc.” Both black and white have as their distinguishing properties the absence of color, and employing the same word for both strikes me as very perceptive of King Arthur’s lexicographer.

In combat with weapons which cut or stab-and in such sports as boxing, baseball and tennis-a participant trained in the use of the right hand will find himself at a disadvantage when confronted unexpectedly with a left-hander. Also, a malevolent left-handed swordsman might be able to come quite close to his adversary with his unencumbered right hand appearing as a gesture of disarmament and peace. But these circumstances do not seem to be able to explain the breadth and depth of antipathy to the left hand, nor the extension of right chauvinism to women-traditional noncombatants.

One, perhaps remote, possibility is connected with the unavailability of toilet paper in preindustrial societies. For most of human history, and in many parts of the world today, the empty hand is used for personal hygiene after defecation, a fact of life in pretechnological cultures. It does not follow that those who follow this custom enjoy it. Not only is it aesthetically unappealing, it involves a serious risk of transferring disease to others as well as to oneself. The simplest precaution is to greet and to eat with the other hand.


Without apparent exception in pretechnological human societies, it is the left hand that is used for such toilet functions and the right for greeting and eating. Occasional lapses from this convention are quite properly viewed with horror. Severe penalties have been visited on small children for breaches of the prevailing handed-ness conventions; and many older people in the West can still remember a time when there were firm strictures against even reaching for objects with the left hand. I believe this account can explain the virulence against associations with “left” and the defensive self-congratulatory bombast attached to associations with “right” which are commonplace in our right-handed society.


The explanation does not, however, explain why the right and left hands were originally chosen for these particular functions. It might be argued that statistically there is one chance in two that toilet functions would be relegated to the left hand. But we would then expect one society in two to be righteous about leftness. In fact, there seem to be no such societies. In a society where most people are right-handed, precision tasks such as eating and fighting would be relegated to the favored hand, leaving by default toilet functions to the side sinister. However, this also does not account for why the society is right-handed. In its most fundamental sense, the explanation must lie elsewhere.

There is no direct connection between the hand you prefer to use for most tasks and the cerebral hemisphere that controls speech, and the majority of left-handers may still have speech centers in the left hemisphere, although this point is in dispute.

Nevertheless, the existence of handedness itself is thought to be connected with brain lateralization. Some evidence suggests the left-handers are more likely to have problems with such left-hemisphere functions as reading, writing, speaking and arithmetic; and to be more adept at such right-hemisphere functions as imagination, pattern recognition and general creativity.*


* The only left-handed American presidents have apparently been Harry Truman and Gerald Ford. I am not sure whether this is consistent or inconsistent with the proposed (weak) correlation between handedness and hemisphere function. Leonardo da Vinci may be the most illuminating example of the creative genius of left-handers.


Some data suggest that human beings are genetically biased towards right-handedness. For example, the number of ridges on fingerprints of fetuses during the third and fourth months of gestation is larger in the right hand than the left hand, and this preponderance persists throughout fetal life and after birth.

Information on the handedness of the Australopithecines has been obtained from an analysis of fossil baboon skulls fractured with bone or wooden clubs by these early relatives of man. The discoverer of the Australopithecine fossils, Raymond Dart, concluded that about 20 percent of them were left-handed, which is roughly the fraction in modern man. In contrast, while other animals often show strong paw preferences, the favored paw is almost as likely to be left as right.


The left/right distinctions run deep into the past of our species. I wonder if some slight whiff of the battle between the rational and the intuitive, between the two hemispheres of the brain, has not surfaced in the polarity between words for right and left: it is the verbal hemisphere that controls the right side. There may not in fact be more dexterity in the right side; but it certainly has-a better press.


The left hemisphere seems to feel quite defensive-in a strange way insecure-about the right hemisphere; and, if this is so, verbal criticism of intuitive thinking becomes suspect on the ground of motive. Unfortunately, there is every reason to think that the right hemisphere has comparable misgivings -expressed nonverbally, of course-about the left.

Admitting the validity of both methods of thinking, left hemisphere and right hemisphere, we must ask if they are equally effective and useful in new circumstances. There is no doubt that right-hemisphere intuitive thinking may perceive patterns and connections too difficult for the left hemisphere; but it may also detect patterns where none exist. Skeptical and critical thinking is not a hallmark of the right hemisphere. And unalloyed right-hemisphere doctrines, particularly when they are invented during new and trying circumstances, may be erroneous or paranoid.

Recent experiments by Stuart Dimond, a psychologist at University College, Cardiff in Wales, have employed special contact lenses to show films to the right or left hemisphere only. Of course, the information arriving in one hemisphere in a normal subject can be transmitted via the corpus callosum to the other hemisphere. Subjects were asked to rate a variety of films in terms of emotional content.


These experiments showed a remarkable tendency for the right hemisphere to view the world as more unpleasant, hostile, and even disgusting than the left hemisphere. The Cardiff psychologists also found that when both hemispheres are working, our emotional responses are very similar to those of the left hemisphere only. The negativism of the right hemisphere is apparently strongly tempered in everyday life by the more easygoing left hemisphere.


But a dark and suspicious emotion tone seems to lurk in the right hemisphere, which may explain some of the antipathy felt by our left hemisphere selves to the “sinister” quality of the left hand and the right hemisphere. In paranoid thinking a person believes he has detected a conspiracy-that is, a hidden (and malevolent) pattern in the behavior of friends, associates or governments-where in fact no such pattern exists. If there is such a conspiracy, the subject may be profoundly anxious, but his thinking is not necessarily paranoid.


A famous case involves James Forrestal, the first U.S. Secretary of Defense. At the end of World War II, Forrestal was convinced that Israeli secret agents were following him everywhere. His physicians, equally convinced of the absurdity of this idee fixe, diagnosed him as paranoid and confined him to an upper story of Walter Reed Army Hospital, from which he plunged to his death, partly because of inadequate supervision by hospital personnel, overly deferential to one of his exalted rank. Later it was discovered that Forrestal was indeed being followed by Israeli agents who were worried that he might reach a secret understanding with representatives of Arab nations.


Forrestal had other problems, but having his valid perception labeled paranoid did not help his condition.

In times of rapid social change there are bound to be conspiracies, both by those in favor of change and by those defending the status quo, the latter more than the former in recent American political history. Detecting conspiracies when there are no conspiracies is a symptom of paranoia; detecting them when they exist is a sign of mental health. An acquaintance of mine says, “In America today, if you’re not a little paranoid you’re out of your mind.”


The remark, however, has global applicability.

There is no way to tell whether the patterns extracted by the right hemisphere are real or imagined without subjecting them to left-hemisphere scrutiny. On the other hand, mere critical thinking, without creative and intuitive insights, without the search for new patterns, is sterile and doomed. To solve complex problems in changing circumstances requires the activity of both cerebral hemispheres: the path to the future lies through the corpus callosum.


An example of different behavior arising from different cognitive functions-one example of many-is the familiar human reaction to the sight of blood. Many of us feel queasy or disgusted or even faint at the sight of copious bleeding in someone else. The reason, I think, is clear. We have over the years associated our own bleeding with pain, injury, and a violation of bodily integrity; and we experience a sympathetic or vicarious agony in seeing someone else bleed.


We recognize their pain. This is almost certainly the reason that the color red is used to signify danger or stop * in many diverse human societies. (If the oxygen-carrying pigment in our blood were green-which biochemically it could have been-we would, all of us, think green a quite natural index of danger and be amused at the idea of using red.)


* Or down, as in elevator direction lights. Our arboreal ancestors had to be very careful about down.


A trained physician, on the other hand, has a different set of perceptions when faced with blood. What organ is injured? How copious in the bleeding? Is it venous or arterial flow? Should a tourniquet be applied? These are all analytic functions of the left hemisphere. They require more complex and analytic cognitive processes than the simple association: blood equals pain. And they are far more practical. If I were injured, I would much rather be with a competent physician who through long experience has become almost entirely inured to gore than with an utterly sympathetic friend who faints dead away at the sight, of blood.


The latter may be highly motivated not to wound another person, but the former will be able to help if such a wound occurs. In an ideally structured species, these two quite different attitudes would be present simultaneously in the same individual. And in most of us that is just what has happened. The two modes of thinking are of very different complexity, but they have complementary survival value.

A typical example of the occasional resistance mustered by intuitive thinking against the clear conclusions of analytical thinking is D. H. Lawrence’s opinion of the nature of the moon:

“It’s no use telling me it’s a dead rock in the sky! I know it’s not.”

Indeed, the moon is more than a dead rock in the sky. It is beautiful, it has romantic associations, it raises tides, it may even be the ultimate reason for the timing of the human menstrual cycle. But certainly one of its attributes is that it is a dead rock in the sky. Intuitive thinking does quite well in areas where we have had previous personal or evolutionary experience.


But in new areas-such as the nature of celestial objects close up-intuitive reasoning must be diffident in its claims and willing to accommodate to the insights that rational thinking wrests from Nature. By the same token, the processes of rational thought are not ends in themselves but must be perceived in the larger context of human good; the nature and direction of rational and analytical endeavors should be determined in significant part by their ultimate human implications, as revealed through intuitive thinking.

In a way, science might be described as paranoid thinking applied to Nature: we are looking for natural conspiracies, for connections among apparently disparate data. Our objective is to abstract patterns from Nature (right-hemisphere thinking), but many proposed patterns do not in fact correspond to the data. Thus all proposed patterns must be subjected to the sieve of critical analysis (left-hemisphere thinking). The search for patterns without critical analysis, and rigid skepticism without a search for patterns, are the antipodes of incomplete science. The effective pursuit of knowledge requires both functions.

Calculus, Newtonian physics and geometrical optics were all derived by fundamentally geometrical arguments and are today taught and demonstrated largely by analytical arguments: creating the mathematics and physics is more of a right-hemisphere function than teaching it. This is common today as well. Major scientific insights are characteristically intuitive, and equally characteristically described in scientific papers by linear analytical arguments. There is no anomaly in this: it is, rather, just as it should be. The creative act has major right-hemisphere components. But arguments on the validity of the result are largely left-hemisphere functions.

It was an astonishing insight by Albert Einstein, central to the theory of general relativity, that gravitation could be understood by setting the contracted Riemann-Christoffel tensor equal to zero. But this contention was accepted only because one could work out the detailed mathematical consequences of the equation, see where it made predictions different from those of Newtonian gravitation, and then turn to experiment to see which way Nature votes. In three remarkable experiments-the deflection of starlight when passing near the sun; the motion of the orbit of Mercury, the planet nearest to the sun; and the red shift of spectral lines in a strong stellar gravitational field- Nature voted for Einstein.


But without these experimental tests, very few physicists would have accepted general relativity. There are many hypotheses in physics of almost comparable brilliance and elegance that have been rejected because they did not survive such a confrontation with experiment. In my view, the human condition would be greatly improved if such confrontations and willingness to reject hypotheses were a regular part of our social, political, economic, religious and cultural lives.

I know of no significant advance in science that did not require major inputs from both cerebral hemispheres. This is not true for art, where apparently there are no experiments by which capable, dedicated and unbiased observers can determine to their mutual satisfaction which works are great. As one of hundreds of examples, I might note that the principal French art critics, journals and museums of the late nineteenth and early twentieth centuries rejected French Impressionism in toto; today the same artists are widely held by the same institutions to have produced masterpieces. Perhaps a century hence the pendulum will reverse direction again.

This book itself is an exercise in pattern recognition, an attempt to understand something of the nature and evolution of human intelligence, using clues from a wide variety of sciences and myths. It is in significant part a right-hemisphere activity; and in the course of writing it I was repeatedly awakened in the middle of the night or in the early hours of the morning by the mild exhilaration of a new insight.


But whether the insights are genuine-and I expect many of them will require substantial revision-depends on how well my left hemisphere has functioned (and also on whether I have retained certain views because I am unaware of the evidence that contradicts them). In writing this book I have been repeatedly struck by its existence as a meta-example: in conception and execution it illustrates its own content.

In the seventeenth century there were two quite distinct ways of describing the connection between mathematical quantities: you could write an algebraic equation or you could draw a curve. Rene Descartes showed the formal identity of these two views of the mathematical world when he invented analytical geometry, through which algebraic equations can be graphed.

(Descartes, incidentally, was also an anatomist concerned about the localization of function in the brain.)


Analytical geometry is now a tenth-grade commonplace, but it was a brilliant discovery for the seventeenth century. However, an algebraic equation is an archetypical left-hemisphere construction, while a regular geometrical curve, the pattern in an array of related points, is a characteristic right-hemisphere production. In a certain sense, analytical geometry is the corpus callosum of mathematics.


Today a range of doctrines find themselves either in conflict or without mutual interaction. In some important instances, they are left-hemisphere versus right-hemisphere views. The Cartesian connection of apparently unrelated or antithetical doctrines is sorely needed once again.

I think the most significant creative activities of our or any other human culture-legal and ethical systems, art and music, science and technology-were made possible only through the collaborative work of the left and right cerebral hemispheres. These creative acts, even if engaged in rarely or only by a few, have changed us and the world.


We might say that human culture is the function of the corpus callosum.


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