Who Am I and If So How Many? (4 page)

There is little doubt that the size and structure of the human brain was the determining factor in the development and
incomparable cultural achievements of modern man. But why did man wait so long to put the human brain’s capacity for technical innovation to use? Evidently the brain needed to fulfill very different functions back then. Today’s great apes, whose use of tools is just as primitive as that of the australopithecines, are clearly more intelligent than a simple use of rocks and branches would require. Great apes use the far greater part of their intelligence for their complex social interaction, and even for humans the greatest daily challenge is dealing with members of our own species. (See ‘The Sword of the Dragon Slayer,’ p. 99.) Still, we use only a fraction of our brain capacity, because intelligence comes into play only when we reach an impasse. Even if primatologists had trained their binoculars on Albert Einstein the way they now observe apes, they would have seen little out of the ordinary. Einstein did not make much use of his genius in his normal daily routines – sleeping, dressing, eating, and so forth – because brilliant ideas and inspiration are simply unnecessary for those activities.

The human brain is impressive, but most of the time it runs on a low level, just as our forefathers’ brains did. Like apes, humans have instincts for war and aggression and possess a sense of family and community. The more we learn about the lives of animals, the more clearly we recognize ourselves, and the more we see the echo from 250 million years of mammalian development in the convolutions of our brains.

Nietzsche’s clever animals are thus truly animals, but their unparalleled intellect still remains an enigma. Some philosophers in the early-nineteenth-century Romantic era insisted on regarding man as nature’s crowning achievement – as the creature created to understand the world and to make nature aware of itself. In reality, of course, there is no reason to believe that man and his actions are the goal of evolution, and indeed even the concept of a ‘goal’ itself is dubious. Goals represent a very human approach to thinking (do salamanders have goals?) and are associated with typically human notions of time, as are the terms ‘progress’ and ‘meaning.’ But nature is physical, chemical, and biological, and
the term ‘meaning’ is on an entirely different plane from, say, the term ‘protein.’

The cleverer among Nietzsche’s clever animals – namely, those who have grasped this – do not focus on the big picture of ‘objective’ reality, but instead ask themselves: What am I capable of knowing? And how does this ability to know
function
? Philosophers like to speak of a ‘cognitive turn’ to the foundations of our self-awareness and our understanding of the world. To probe this idea, I would like to take you along on a journey to the foundations of our knowledge. Let us fly with Lucy into a cosmos more exhilarating than just about anything philosophers in earlier eras could visit; let us explore the center of feeling and thinking, and voyage inside our brains.

What is the most complex thing in the world? That is a difficult question, but for science, the answer is clear: it is the human brain. Granted, there is nothing particularly spectacular about it on the outside. At barely three pounds, it is shaped like a giant walnut and has the consistency of a soft-boiled egg. But hidden within it is likely the most complex mechanism in the universe, with 100,000,000,000 (one hundred billion) neurons firing and up to 500,000,000,000,000 (half a quintillion) connections between them. A common analogy holds that there are about as many leaves on the trees in the Amazon rainforest as there are neuron connections in a human brain.

Until about 120 years ago, we knew next to nothing about what goes on inside the brain. Anyone who was writing or speculating about the brain before that time was merely skimming the surface, which makes it all the more astonishing that the first scientist to interpret the overall operations of the brain and decipher its basic mechanisms is today virtually unknown. His name – Santiago Ramón y Cajal – ought to appear on any objective list of the most important researchers and thinkers of the twentieth century, yet relatively little has been written about him.

Ramón y Cajal was born in 1852 in Navarra, Spain, in the town of Petilla de Aragón. He was eight years younger than Nietzsche, and at the time of the Spaniard’s birth and early childhood, Darwin was in Downe, a few miles south of London, working on his magnum opus,
Origin of Species
. Ramón y Cajal did not originally intend to study biology; he had always dreamed of becoming a painter. When he was a young man, he and his father dug up bones at a former cemetery to study the human body. Ramón y Cajal’s father was on the faculty of the anatomy department at the hospital in Zaragoza, where he practiced surgery. Working with these bones eventually drew Ramón y Cajal away from painting to anatomy. In stark contrast to the great Darwin, who had broken off his study of medicine because he was revolted by the need to dissect cadavers, Ramón y Cajal’s examinations of corpses fired up his enthusiasm, and he became a doctor at the age of twenty-one. His fascination with corpses and skeletons also led him to join the army. From 1874 to 1875, he took part in an expedition to Cuba, where he contracted malaria and tuberculosis. Upon his return, he became an intern at the University of Zaragoza medical school. In 1877, the
Complutense
University of Madrid awarded him a doctorate. As a professor of descriptive and general anatomy at the University of Valencia, he began to discover the magic of the brain. Why had no one ever made a thorough study of the human brain, beyond its basic anatomical structures? Ramón y Cajal came up with an ambitious plan: he would find out what he could about the
processes
in the brain and establish a new science he would call ‘rational psychology.’ Piece by piece, he examined the cellular tissue of the human brain under the microscope and sketched what he saw. In 1887, he was appointed professor of histology and pathology at the University of Barcelona, and in 1892, he joined the faculty of the Complutense University of Madrid, the largest and most renowned university in Spain. In 1900, he also became the director of the National Institute of Hygiene and of the Investigaciones Biológicas.

A photograph shows a bristly-bearded Ramón y Cajal in his book-filled study in Madrid, his head resting on his right hand and his deep-set dark eyes gazing at a human skeleton. Another picture captures him in a similar pose in his laboratory wearing an Eastern-looking lab coat and a Maghrib cap, looking more like a painter than a scientist. As he grew older, his face took on a sinister aspect, suggesting a shifty Hollywood character or a mad scientist in league with the devil. In fact, Ramón y Cajal was anything but sinister. His contemporaries liked and respected him greatly. He was modest, generous, and easygoing, and he had a good sense of humor.

Ramón y Cajal examined the dead brains of humans and animals. Unfortunately for him, the time was not yet ripe for research on living brains. How could people find out how the brain functioned if its processes could not be observed in action? Still, Ramón y Cajal’s accomplishments were nothing short of amazing. The only thing about him that might be called demonic was his remarkable ability to bring dead neurons to life. He fancied himself a friendly Frankenstein, describing the brain cell sequences he observed under the microscope as though he were actually watching them at work. His essays and books provide spirited descriptions of dynamic activity, with neurons feeling, acting, and anticipating, emergent fibers groping to find others. Ramón y Cajal’s description of this microstructure laid the foundation for the modern study of the brain’s nervous system, and during his long years as a researcher, he wrote 270 scientific essays and eighteen books, which made him perhaps the most important neuroscientist of all time. In 1906 he was awarded the Nobel Prize in the category of Physiology or Medicine.

Ramón y Cajal’s research was so noteworthy because neurons in the brain did not resemble normal somatic cells, and their odd, irregular shapes and many fine extensions had baffled scientists before him. Ramón y Cajal drew highly detailed sketches of these cells with their strange cobweb patterns that looked like bits of algae strung together. Although he did not actually coin any of the
key terms that are still used today, he described the elements of the nervous system in the brain more precisely than anyone before him had. He drew and explained the neurons and the axons, which are the long fibers on both sides of the neurons. He described in detail the branched projections, known as dendrites, for the first time. He adopted the word ‘synapses’ from his British friend and colleague Charles Scott Sherrington to describe the neural communication points at the ends of the dendrites. Ramón y Cajal’s meticulous studies yielded a veritable alphabet of neurons in the brain, but he had to use his imagination to generate the corresponding mental grammar, and even more to envisage the spoken language of his neurons in what he called ‘neuronal circuits.’

Much of what Ramón y Cajal assumed later proved to be correct. His key assumptions were that nerve impulses were conducted in only one direction on their path through the brain and the spinal cord, and that the synapses of one neuron communicated with the synapses of another. He correctly hypothesized that nerve tracts are one-way streets – an information flow is never reversible. Of course Ramón y Cajal was working with dead brains, which gave no indication of electrical or chemical activity, so he was unable to demonstrate how the synapses communicated. Still, even if he was not able to see these signal transmissions in action, he knew that they occurred, because the German physiologist Otto Loewi had shown in 1921 that nerve impulses are transmitted chemically, not electronically.

Ramón y Cajal died in 1934 at the age of eighty-two. Over the following three decades, some scientists in Europe, the United States, and Australia investigated the basic mechanisms of
electrochemical
signal transmission in the brain, while others aimed to provide a more precise interpretation of the individual areas in the brain. What was responsible for what, and why? Attention focused on Paul MacLean’s clear-cut model of a triune brain, which MacLean developed in the 1940s. Since man had developed from the lower animals, MacLean postulated that the different regions of the human brain corresponded to the different stages of human
development. In his model, the brain is actually made up of three distinct brains. The first is a primitive reptilian brain, which consists primarily of the brain stem and the cerebellum and constitutes the ‘lowest’ form of the brain, where innate instincts are located. According to MacLean, the primitive reptilian brain is nearly incapable of learning and has no role in social interaction. He called the second brain the ‘Paleomammalian brain’ and argued that it corresponded to the
limbic system
– the locus not only of instinctual drives and emotions but also of nature’s early attempt to develop a consciousness and a memory. The third brain, the ‘neomammalian brain,’ corresponds to the
neocortex
as the seat of reason, understanding, and logic. In MacLean’s schema, the neomammalian brain works irrespective of the regions of the brain that preceded it in our evolutionary heritage. MacLean argued that there are few connections between the brain’s three component parts. Feelings and intellect, he claimed, are controlled by two different brains, which helped explain why our intellect has so much trouble exercising control over our feelings.

MacLean’s neat little divisions were easy to grasp, and they quickly caught on. He subdivided the brain into three to mirror the distinctions philosophers had been drawing for two millennia among animal instincts, higher feelings, and clever human reason. The only problem was that MacLean’s theory, which can still be found in many textbooks today, is wrong. The human brain is not made up of three essentially independent brains. And the simple idea that the three brains originated sequentially in the
development
from reptile to man is incorrect. Reptiles also have a limbic system that is quite similar to that of man, as well as an endbrain, a simpler variant of the neocortex in mammals. But the crucial point is that the connections among the brain stem, cerebellum, and cerebrum are actually very close; they are not simply stacked on top of one another, as MacLean had suggested. Their tight and complex connection is extremely important and is our key to understanding the way instincts, sensations, volition, and cognition really function.

Much of what brain researchers have surmised about our brains over the past hundred years has been subject to ongoing revision. In the 1820s, the French physiologist Jean Pierre Marie Flourens (who later became a sworn enemy of Darwin) had established that many brain functions are interrelated. He had removed various parts of the brain, one by one, from various laboratory animals, especially rabbits and pigeons, to see which functions subsequently ceased. To his astonishment, he found no reduction in individual capabilities; many became worse in clusters, somewhat like the computer HAL in Stanley Kubrick’s 2001:
A Space Odyssey
, which became slower and more sluggish as a whole as each memory module was removed from service. Flourens realized that the old model of brain regions that governed discrete abilities such as addition and subtraction, speech, thought, and memory was incorrect, but he went too far the other way in claiming that everything in the brain was responsible for everything else. The generation between Flourens and Ramón y Cajal focused on tracking down and sorting out the areas and centers of the brain according to basic functions. Every self-respecting researcher drew an atlas of the brain. The most spectacular discoveries in this field were made by the French anatomist Paul Broca and the German neurologist Carl Wernicke, when the two of them, independently of each other, identified two distinct speech centers in the human brain:
Broca’s area
for speech production, in 1861, and
Wernicke’s
area
for speech comprehension, in 1874.

Today the brain is divided up into the brain stem, the diencephalon, the cerebellum, and the cerebrum. The
brain stem
, located in the middle of the head, constitutes the lowest segment of the brain and consists of the mid-brain, the pons, and the medulla oblongata. The brain stem communicates sense
impressions
and coordinates our involuntary movements, such as heartbeat, breathing, and metabolism, and our reflexes, including blinking, swallowing, and coughing.

The
diencephalon
is a relatively small area above the brain stem, consisting of the upper part of the thalamus, the hypothalamus, the
subthalamus, and the epithalamus. Its role is essentially that of an agent and emotional evaluator. It registers sense impressions and conveys them to the cerebrum. As a sensitive system of nerves and hormones, the diencephalon controls our sleeping and waking, our sensations of pain, the regulation of our body temperature, and our drives and instincts, such as our sex drive.

The
cerebellum
has a major influence on our motility and our motor learning. In other vertebrates it is much more prominent than in man, especially in fish, whose movements somehow seem more sophisticated than those of humans. In our species, the cerebellum also governs unconscious tasks involving cognitive acts, speech, social conduct, and memory.

The
cerebrum
is located above the three other regions; in man it is more than three times as large as the other parts of the brain put together. It can be divided into numerous regions, which can in turn be subdivided into the ‘simpler’ sensory areas and the ‘higher’ associative areas. All complex human mental functions depend heavily, though not exclusively, on the activity of the associative cortex.

Our cognitive performance is dependent on what we
experience
, as Immanuel Kant pointed out in the opening sentences of his magnum opus, the
Critique of Pure Reason
:

Our attentiveness determines our feelings and thoughts, just as our feelings and thoughts determine our attentiveness. People can focus on only one thing at a time; so-called multitasking does not
mean that we are able to concentrate on several things at once, but only that we switch back and forth very quickly. The range of our attention is often compromised in the process, not only by our biologically determined perceptive capabilities but also by our limited capacity to engage the full range of our neurons in the brain. We use only a fraction of our brain capacity, and it is difficult to expand this range. Our attentiveness comes up against limits, and when we focus on one thing, other things recede into the background. My four-year-old son Oskar is fascinated by animals and can tell me the names of many different kinds of dinosaurs and distinguish between eared sea lions and earless seals, yet he still has trouble putting on a T-shirt by himself. It is not the sum of our neurons but our attention span that limits our learning ability.