Leonardo's Brain Read online

  Leonardo designed greatly improved pontoon bridges, collapsible bridges, and swing bridges. His most ambitious project was a bridge across the Bosphorous, designed for the Ottoman Empire. The Florentines were on friendly terms with the Turks when Leonardo was a young man. In his letter to the Sultan, Leonardo wrote: “I have heard that you intend to build a bridge from Galata to Constantinople but that you have not built it for want of a skilled master [architect].” Leonardo proposed building a bridge beneath which sailing ships could pass. The bridge would have been 766.7 feet above water. These dimensions are clearly fantastic. The largest bridge of this type at that time was over the Adda. Constructed from 1370 to 1377, it had a span of 235 feet and was 68 feet high. Five hundred years later, the Norwegians, using Leonardo’s design, built a bridge that complies with his specifications.

  Leonardo also turned his considerable attention to travel in, under, and on the water. He invented life preservers, webbed gloves, and the snorkel to improve the performance and safety of swimmers. For activity beneath the surface, he designed a diving suit and the mask to go with it (as well as the submarine). He greatly improved on the design of paddleboats, and invented the first water lock, whose importance to modern river navigation cannot be overemphasized.

  Had they been known at the time, Leonardo’s inventions relating to hydraulics would have transformed the field. He designed greatly improved waterwheels and well pumps. His drawings of mechanical devices remain among the most beautiful renderings of machines and their components in all of art. Among his inventions were the spinning machine, treadle-operating lathes, file-making machines, mechanical saws, horizontal and vertical metal-boring machines, stone-cutting machines, and a clever rope-spinning device. He also invented the metal screw and the concept behind prefabricated buildings.

  He measured the tensile strength of various materials, created novel designs for pulleys, and an innovative two-wheeled hoist. In his art we find the first rendering of a foundrylike factory and designs for improved cranes. He understood the potential of machines better than any of his contemporaries and constantly explored how mechanical contrivances could ease the burden of humans. In his many technological and engineering feats, Leonardo anticipated the machine-driven Industrial Revolution by 350 years.

  He made robots that operated on computerlike programs to delight potential patrons. When the King of France visited Milan, Leonardo programmed a mechanical lion to walk down the aisle, approach the king, and then stop. Then, its chest opened to spill forth the fleur-de-lis. Both the lion and the flower symbolized the French throne. Mark Elling Rosheim, a modern expert on robots, has concluded that Leonardo’s lion represented the first true robot.

  To aid in his scientific endeavors, Leonardo invented many measuring devices. He greatly improved on the design of clocks. He invented meters to measure water flow and anemometers to gauge wind speed. The modern hygrometer, used to measure humidity in the air, was not invented until 1783 by the Swiss Horace-Bénédict de Saussure, but Leonardo had already made a working model several centuries earlier.

  Among the many disappointments that Leonardo had to confront in his life was the fact that none of his innovative architectural plans ever came to fruition. Throughout his notebooks are many drawings for buildings that contain novel ideas but, as best we know, not a single one of his concepts ever became a reality during his lifetime.

  Because of the exceptional detail of Leonardo’s anatomical drawings, his contributions to the fields of physiology, anatomy, and comparative anatomy are among his most familiar. As a result of his investigations, Leonardo made many groundbreaking discoveries and, in addition, left posterity some of the most beautiful renderings of the interior of the human body anyone has ever created.

  Leonardo’s desire to more accurately draw the human body increased his interest in studying how everything was integrated. He castigated Michelangelo’s rendering of human musculature, writing that his rival’s style resembled a “sack of walnuts.” He felt that this other titan of his age had insufficiently studied the human body, and as a result rendered the muscles of his figures in an exaggerated and inaccurate manner.

  Leonardo corrected the mistaken belief that the human heart contained two chambers. His dissections revealed all four, and he methodically described them, their interior, and their relationship to each other. He came remarkably close to uncovering the secret of human circulation, discovered by William Harvey in 1628. Harvey, like Leonardo, understood that the heart was a pump, but the lack of a microscope (a device that had not yet been invented) hampered both men’s conceptualization. Neither could explain how arterial blood traversed over to the venous side because the capillaries that served as conduits were too small to see with the naked eye.

  Leonardo, enamored with the idea that the human body was a microcosm of the larger Earth, believed erroneously that the blood ebbed and flowed rather than circulating in a continuous loop. Nevertheless, Leonardo’s description of the heart, coronary arteries, heart valves, aorta, major arteries, and venous valves was truly groundbreaking.

  Leonardo considered making a super drawing that would overlay the ten individual ones he had drawn of the foot, revealing the relations of the nerves, arteries, bones, muscles, and lymph nodes: “You could make the eleventh in the form of a transparent foot, in which you could see all the aforesaid things.”

  Leonardo’s contributions to the field of neuroscience are sufficient to claim that Leonardo was history’s earliest neuroanatomist. He was the first to describe in detail the ventricles of the brain and first to identify the crossing over of the portions of optic nerves to the opposite hemisphere in what is now known as the optic chiasma. He postulated that nerve impulses traveled as waves along a nerve’s length. Although he was mistaken concerning the manner by which these waves propagated, his basic assumption was correct. His interest in ophthalmology led him to correctly identify how the lens of the eye inverts the image that we see on the retina upside down.

  His amazement while contemplating the service that the eye performed led him to write passionately:

  The eye, which is the window of the soul, is the chief organ whereby the understanding can have the most complete and magnificent view of the infinite works of nature.

  Now do you not see that the eye embraces the beauty of the whole world? . . . It counsels and corrects all the arts of mankind. . . . It is the prince of mathematics, and the sciences founded on it are absolutely certain. It has measured the distances and sizes of the stars; it has discovered the elements and their location. . . . It has given birth to architecture and to perspective and the divine art of painting.

  Oh, excellent thing, superior to all others created by God! What praises can do justice to your nobility? What peoples, what tongues will fully describe your function? The eye is the window of the human body through which it feels its way and enjoys the beauty of the world. Owing to the eye the soul is content to stay in its bodily prison, for without it such bodily prison is torture.

  O marvelous, O stupendous necessity, thou with supreme reason compellest all effects to be the direct result of their causes; and by a supreme and irrevocable law every natural action obeys thee by the shortest process possible. Who would believe that so small a space could contain all the images of the universe . . .

  Botany was another field in which Leonardo reigned as a master. His desire to accurately render various species of plants and trees in his paintings encouraged him to begin to study the diversity of the plant world. Leonardo’s consuming desire to solve the mystery of plants and flowers led him to make critical discoveries concerning the physiology of botany. He was the first botanist to recognize that a tree’s cambrium, the layer lying just beneath the bark, is the most essential component of the plant. He also described how the tree’s sap serves the same circulatory function that blood does in an animal: transporting nutrients and eliminating wastes. He described in detail the phenomenon of phyllotaxis, a complex theory about how the
leaves are arranged on the stem of a plant. When he realized that one could assess a tree’s age by counting its rings, he single-handedly founded the field of dendrochronology. He even speculated correctly that each ring contained information concerning the temperature and climate of any particular year of the tree’s life by comparing the thickness of any one ring to the others.

  Leonardo also investigated the beginnings of human life. He dissected the uterus of a recently deceased pregnant woman and methodically drew the position of the fetus in her womb. He identified the umbilical cord as the source of nourishment for the fetus and pronounced, contrary to the commonly held beliefs of his day, that “The seed of the mother has equal power in the embryo to the seed of the father.” (Living in an extremely patriarchal society, this was an unusually generous egalitarian conclusion.) His interest in embryology resulted in his dissecting other dead pregnant animals to record the rates of growth of their fetuses. His studies cement his right to be considered history’s first embryologist.

  Leonardo was the first to diagnose arteriosclerosis. He attended an old man who died a gentle death before his eyes and then immediately conducted the first recorded modern autopsy, observing that the deceased man’s aorta was clogged with plaque. He correctly deduced that a diminishment of blood flow secondary to constriction of the artery’s inner diameter was the immediate cause of death. This single postmortem followed by the correct diagnosis qualifies Leonardo to be the founder of pathology. While Hippocrates and other classical physicians had made diagnoses based on symptoms correlated with physical findings, it is doubtful that anyone before Leonardo had actually conducted a fresh autopsy to determine the cause of death.

  At one point Leonardo spoke of 120 books he had composed on anatomy. Antonio de Beatis, secretary to the Cardinal of Aragon, reported that Leonardo da Vinci “wrote a remarkable work on the relation of anatomy to painting; he describes the bones, members, muscles, sinews, veins, joints, internal organs, in a word, all that is necessary for studying both the male and the female body, and which no one had done before him.” And he added, “We ourselves saw this work.”

  Leonardo’s interest in anatomy also led him to ponder the similarities between humans and other animals. He dissected a bear’s hind limb and observed that the muscles and tendons were remarkably similar to those of a human. He concentrated his greatest efforts on an animal other than his own species in exploring the frame and musculature of the horse, prompted, no doubt, by his desire to cast in bronze the largest man-on-a-horse statue ever attempted. In preparation for this task, he made the first detailed studies of equine anatomy.

  His observations concerning the close similarities between the anatomy of other higher animals and those of humans constitutes history’s first foray into the field of comparative anatomy. When combined with his understanding that the Earth was exceedingly old, had he published his findings, they would most likely have dramatically sped the elaboration of the theory of evolution that had to wait more than three centuries for Darwin’s grand insight.

  Compounding all these achievements, we surely have a scientific genius the likes of which the world had never seen before or since. Leonardo foreshadowed future technologies by hundreds of years. He was the first and preeminent futurist.

  Chapter 13

  Emotions/Memory

  If the body of every feeding thing continually dies and is continually reborn, how can that art be “most noble” which can engrave only a single moment?

  —Leonardo da Vinci

  The latter condition is demonstrated in an example offered by Goldstein, in which he described a patient who attempted to strangle herself with one hand and to release the strangling hand with the other. On postmortem examination it was found that she had suffered from a dissecting tumor of the corpus callosum.

  —James S. Grotstein

  There is a female human nature and a male human nature, and these natures are extraordinarily different. . . . Men and woman differ in their sexual natures because throughout the immensely long hunting and gathering phase of human evolutionary history, the sexual desires and dispositions that were adaptive for either sex were for the other tickets to reproductive oblivion.

  —Donald Symons

  In the late seventeenth century, the mathematician Blaise Pascal described two different mental operations. The first he characterized as the sudden grasp of knowledge leading to a total comprehension of all facets of a concept simultaneously; the other was patient analytical reasoning, proceeding in a sequential fashion. When he wrote, “The heart has its reasons which reason knows nothing of,” he was unaware that he was distinguishing between the kind of knowing that goes on in the emotional right brain and that which occurs in the cerebral left. Pascal was the first scientist to acknowledge the division between the right and left brain.

  I will focus on the brain organization of someone who is right-handed and left-brain-dominant. I do not wish to dismiss the 8 to 12 percent of the population who are left-handed; rather, I wish to use the most universal model. The dysfunction that occurs as a result of left-brain injury in right-handers is so great that the left cerebral hemisphere has come to be known as the dominant lobe. Adopting this convention, I shall refer to the left brain as the dominant hemisphere.

  If a right-handed person has a major stroke in the controlling left hemisphere, a catastrophic dysfunction of speech, motor activity, or abstract thinking will occur. Conversely, a significant stroke in the right brain can impair an individual’s ability to solve spatial problems, recognize faces, or appreciate music.

  The right side of the brain is the elder sibling. In utero, the right lobe of a human fetus’s brain is well on its way to maturation before the left side even begins to develop. The old, wise, right side is more familiar with the needs and drives stemming from earlier stages of evolution than the younger left side. The right brain is largely nonverbal and has more in common with earlier animal modes of communication. It comprehends the language of cries, gestures, grimaces, cuddling, suckling, touching, and body stance. Its emotional states are under little volitional control and betray true feelings through fidgeting, blushing, or smirking. More than the left, the right expresses being—that complex meshing of emotions that constitute our existential state at any given moment.

  The right brain generates the feeling-states that result from combinations of emotions. All feeling states are nonlogical. Feeling-states allow us to have faith in God, to grasp the subtleties of a joke, to experience patriotic fervor, or to be repulsed by a painting someone else finds beautiful. These states all possess a nondiscursive quality. Feeling-states overwhelm the brain’s more recently evolved facility with words. No crisp nomenclature exists to describe them. When pressed to explain their emotional experiences, people, in exasperation, commonly fall back upon tautology—“It is because it is!”

  Emotions are predominantly located to the right of the Great Divide. The principal ones, such as fear, terror, love, hate, shame, disgust, envy, jealousy, and ecstasy are on this side. The only emotions that neuroscientists have identified to reside on the left are those associated with happiness, joy, and cheerfulness.

  Feeling-states do not ordinarily progress in a linear fashion, but are experienced all at once. “Getting” the punch line of a joke results in an explosion of laughter. An intuitive insight arrives in a flash. Einstein reported that he envisioned the idea behind space-time this way, while sitting at his desk in the patent office in Bern, Switzerland; he called it the most ecstatic moment of his entire life. Kandinsky was shocked by his realization that an abstract image was equal to an illustrative one. Both of these are examples are what the poet Rainer Maria Rilke called a “conflagration of clarity.” Love at first sight, such as what Dante experienced when he encountered Beatrice, happens in an instant. (She was eight years old, wearing a red dress.) Religious conversions, such as the one that overwhelmed Paul on the road to Damascus, strike like lightning.

  The right brain perceive
s the world concretely. A facial expression is “read” without any attempt to translate it into words. The right hemisphere is also the portal leading to the realm of the spiritual. It entertains altered states of consciousness where faith and mystery and the rules of logic do not apply.

  There is compelling evidence that dreaming occurs primarily in the right brain. People who have had a split-brain operation or who have had a stroke in the right brain report less vividness in the imagery of their dreams. On scanners, the right brain shows more activity during REM sleep, the period when dreaming is presumed to take place, than it does during other phases of sleep. Further evidence suggests that dreaming occurs principally in the right hemisphere, because split-brain and brain-injured patients—who verbalize only what is going on in their left brain—have reported a cessation of dreaming.

  Image recognition is the right brain’s forte. It can simultaneously synthesize incongruous elements and integrate the component parts in the field of vision. The right hemisphere can take an entire tableau at a glance and make sense of the grand picture in a holistic manner. It can appreciate the relationship of parts to the whole, and it can also build up a complete picture from just a few fragments. The right side assimilates images as gestalts, which means seeing all at once. Whereas the name of a person is retrieved from the left brain, it is the right side that recognizes that person’s physical being.

  One demonstration of this right-brain skill is the ease with which people can recognize the faces of others. An old friend’s countenance may be altered dramatically by the appearance of wrinkles and baldness, yet we are still able to recognize the childhood pal decades after we last saw him. We do not begin by analyzing his face, building it up from his nose, eyes, and ears. Instead, we recognize him in an instant.