The Brain

A Beginner's Guide

Ammar al-Chalabi, Martin R. Turner, R. Shane Delamont

• Publisher: Oneworld Publications
• Year: 2008
• eBook ISBN: 9781780740539
• Edition: 2
• Topic: Biological Sciences
• Subtopic: Neuroscience
• Index: Biological Sciences

It has been remarked that if the brain were so simple we could understand it, we would be so simple we couldn't. However, as the authors of this accessible guide demonstrate, there are at least some things we do understand about the brain, and this knowedge can shed new light on our conception of ourselves and the workings of our minds. Covering crude ancient neuroscience, sleep, language and even philosophical questions about the nature of consciousness, this lively and entertaining introduction assumes no previous scientific knowledge and will fascinate readers of all backgrounds.

Section 1

Introducing the brain

Introduction: In the beginning . . .

If the brain were so simple we could understand it, we would be so simple we couldn’t.

Lyall Watson (contemporary author)

Thought and intelligence have always been of great importance to humankind and are regarded as the essence of existence: “I think therefore I am,” wrote Descartes in 1641. Yet it is only relatively recently that we have regarded the brain as the source of thoughts, reason, emotion and being. It is now so closely identified with our selves that in many countries brain death is regarded as the same as actual death.

In the great stories of creation, the first thing in existence, before there was even light, was an intelligent mind, because the creation of the universe required a being intelligent enough to design and make it. In the modern scientific version of events, we believe that one of the last things to come into being was an intelligent mind, because something so complex could only arise after many millions of years of evolution. In both cases, intelligence (and by implication the brain) has a special place.

The brain is the most complex object known. It is a chemical and electrical powerhouse, sending messages where needed, in a perfectly targeted way. This soft, grey, one and a half kilogram organ is not only where we experience and manipulate the world but is also responsible for control of our breathing, body temperature, blood pressure and hormones. Billions of nerve cells, each specifically connected to thousands of others, are its essence. Keeping these cells alive and well for a lifetime requires an enormous amount of sophisticated help from the rest of the body and an integrated life support system. To protect the whole from the outside world it is wrapped in a lining, bathed in shock absorbing fluid and packaged in a strong bony box.

But this description does not answer the simplest question: why do we need a brain? Plenty of living things survive perfectly well without a brain and plenty more survive with what can only be described as a trivial collection of nerves. In this book we will try to answer this question and, along the way, explain what the brain is made of, how it is put together, what it does and how it does it.

Modern medicine divides problems with the brain into two groups: neurology and psychiatry, corresponding to problems with the nervous system and problems with the mind. These disciplines attempt to explain disturbances in experience, behaviour, sensation, movement or speech and relate them to physical, chemical or electrical disturbances in the relevant area of the nervous system. Our ancestors did not make such associations, for example believing that seizures were caused by demonic possession, or that hearing voices might be a sign that God was speaking. Many people also believed, and still believe, in another ability of the brain: psychic or paranormal power. These ways of thinking about the brain are important; part of the natural tendency we have to categorize and try to make sense of the world around us. Even modern physics recognizes that simple observation by a conscious being affects the behaviour of the subatomic world; indeed this is a corner-stone of quantum theory. This brings us to the thorny question of consciousness. What is it? What makes it? Are we conscious when we sleep? Is there consciousness after death? These questions have puzzled people for centuries and we will address them here, with an attempt at a modern answer.

Our imaginative brain is what separates us, in our own minds, from other animals. Research is now beginning to show that we are perhaps not so different after all. In this book we want to show that human brains are special and amazing and that although we know an enormous amount about them, there remains far more still to learn. We will start with a look at the past and how people came to realize that the brain is an important organ.

1

The history of the human brain – so it does do something after all

The brain is a world consisting of a number of unexplored continents and great stretches of unknown territory.

Santiago Ramon y Cajal (Spanish physician and anatomist, 1852–1934)

I believe in an open mind, but not so open that your brains fall out.

Arthur Hays Sulzberger (US newspaper publisher, 1891–1968)

Early beliefs – before history began

The brain has no moving parts: unlike the heart, lungs or intestines it does not pulsate, inflate or squeeze. The brain does not make anything: unlike the kidneys, liver or spleen, no urine, bile or lymph comes out of it. Unlike the skin or bones, the brain serves no obvious purpose and yet we now believe it is responsible for thought, emotion and free will. How did we come to such a conclusion and what did people think before? To answer this, we must travel to the past and step from conclusion to conclusion to the present day. We begin this tour with three cautions. First, although our ideas about thinking and emotion stretch back to the earliest recorded civilizations, our knowledge of these early beliefs is based on archaeological evidence and is therefore very patchy. Second, the history of medicine is hugely biased towards Western historical documentation and so we will inevitably mainly describe this view of things. Finally, attitudes to animal and human experiments were quite different in the past and many of the experiments we will describe are quite unpleasant and would be highly unlikely to be allowed today.

Olympic thinkers – the Greeks and their legacy

Never trust anything that can think for itself if you can’t see where it keeps its brain.

J. K. Rowling (Harry Potter and the Chamber of Secrets)

The simple view of the brain as the most fundamental of all organs may seem rather obvious, but even this assumption is based on knowledge largely acquired in the last 200 years. Prior to the Greek philosophers, the heart was widely held to be the seat of intellect. Indeed, a scholar from ancient Egypt, Herodotus (485–425 BCE), writing about mummification, documented the great care taken in the preparation of organs such as the heart, lungs, liver, stomach and intestines, whilst the brain was simply scooped from the skull. The Ancient Egyptians saw the number of visible connections running to and from the heart as evidence for its importance, whereas the brain did not seem to do much. Nevertheless, it was around this time that the first documented ideas about the true function of the brain were recorded, not by the Egyptians, but by the Ancient Greeks.

Opinions on thinking and emotion were, for a time, dominated by three major philosophers but only two of these thought that the brain was important. Hippocrates (460–370 BCE), the “Father of Medicine”, wrote in his book The Sacred Disease,

Men ought to know that from the human brain and from the brain only arise our pleasures, joys, laughter, and jests as well as our sorrows, pains, griefs and tears . . . It is the same thing which makes us mad or delirious, inspires us with dread and fear, whether by night or by day, brings us sleeplessness, inopportune mistakes, aimless anxieties, absent-mindedness and acts that are contrary to habit.

He also noted a fundamental property of the brain’s wiring: damage to the brain on one side produced a bodily deficit on the opposite side.

The philosopher Plato (428–347 BCE) proposed that the “vital principle” lay within the brain, which in conjunction with the spinal cord was responsible for the control of “vital force”. To quote a translation of his work: “Copying the round shape of the universe, they (the gods) confined the two divine revolutions (the eyes) in a spherical body – the head, as we now call it – which is the most divine part of us and lords over all the rest.”

Aristotle (384–322 BCE), however, believed that the function of the brain was to “cool the heart”, although he did also draw the conclusion that the size of this “cooling apparatus” might be linked to overall intelligence. His heart-centred theory was based on his observation that in the embryo the heart is the first organ to develop and is also warmer in temperature, which he felt was a direct measure of an organ’s involvement in vital processes. He also noticed that a chicken exhibited a life of its own, running around after the head was removed, which was further evidence that the heart was needed for action rather than the brain.

A series of Ancient Greek physicians gradually took us, over a number of years, to a more brain-centred view. The first, Strato (340–290 BCE), refined Plato’s original localization of the “vital principle” to the frontal region between the eyebrows, the second, Xenocrates (396–314 BCE), to the crown of the head. The third, Herophilus (335–280 BCE), carried out extensive dissection of the human body and recognized the brain, particularly its base, as the centre of the nervous system, even noticing a difference between nerves for sensation and nerves for action. His discovery of the fluid cavities within the brain, the ventricles, provided the basis for the later “ventricular doctrine” of brain function. Finally, the Alexandrian physician Erasistratus (304–250 BCE) suggested that the greater intelligence of humans might be attributed to the greater number of folds or wrinkles in their brains, compared with those of other animals. However, although more brain-centred ideas were beginning to develop, Aristotle’s view of the brain as a glorified air-conditioner persisted in many circles until medieval times.

“MIKE THE HEADLESS CHICKEN FOR PRESIDENT”

A rather gruesome example of a chicken surviving without a head makes it easier for us to understand exactly why the heart was so long considered the source of thoughts and emotion while the brain was not. “Mike the Headless Chicken” (http://www.miketheheadless-chicken.org) lived on for eighteen months after a failed attempt to kill him. In 1945, he was a rooster destined for his owners’ dinner table. After having his head cut off with an axe, his body ran around, as is usual for chickens. But rather than eventually stopping and dying, he instead “returned to the job of being a normal chicken” and began preening and pecking with his neck. He was fed through an eye dropper until dying one night, apparently from choking. He probably survived because, in a chicken, many reflexes are stored in the spinal cord and brainstem, and the blow was high enough to leave a significant proportion intact. It is thought that he developed a blood clot at the time of the butchery, preventing his death from bleeding. More likely, the blow severed the arteries in such a way that the muscular walls sealed up automatically, as they are designed to. Mike’s spirit is celebrated every May in his home town of Fruita, Colorado.

Over several hundred years, from the third century, one anatomist dominated all thinking: the Greek physician and philosopher Galen (130–200 CE). By dissecting animals (but not humans), he developed anatomical ideas which were taught in all medical schools. His concept of a “physiology of spirits” described a vital force called “pneuma” that, mixed with blood, travelled to the brain, where it was given “animal spirit”. This then controlled the brain, nerves and feelings. The animal spirit was stored in the ventricles (a set of fluid-filled cavities within the brain) and sent through hollow nerves to produce movement and sensation. The fourth century theologian and bishop of Emesa, Nemesius (b. 320 CE), in his work On the Nature of Man, further developed this proposal with the so-called “ventricular doctrine”: the idea that the key elements of imagination, intellect and memory were localized to the ventricular system.

More than a millennium later, in 1543, the Renaissance anatomist, Andreas Vesalius (1514–1564), wrote a detailed anatomical atlas, based on the dissection of human corpses, that challenged Galen’s ideas and forever changed the way anatomy was taught in the west. It was called De Humanis Corpora Fabrica (On the Fabric of the Human Body) and described the five ventricles of the human brain (we now number four of them and name the fifth – see glossary). Vesalius also ascribed three souls to people and assigned to the brain “the chief soul, the sum of the animal spirits, whose functions are distinctly mental”. He was also first to discern the difference between the grey and white matter of the brain. His description referred to the greyish appearance of the thin rim around the main substance of the brain, termed the cortex, contrasted with the whiter-appearing bulk of the brain tissue, its appearance, as we now know, due to the insulation wrapped around the nerves.

Lumps and bumps – the art of phrenology

The first serious attempts at localization of brain function began with the development of phrenology, by the renowned Viennese neuroanatomist Franz Joseph Gall (1758–1828). This doctrine, described in Gall’s work The Anatomy and Physiology of the Nervous System in General, and of the Brain in Particular, saw the excellence of mental faculties or traits as being determined by the size of the brain area upon which they depended, an idea that to some extent we would agree with today. In turn, he thought, the size of these brain areas could be judged by the development of the skull and the bumps overlying each area, an idea we now consider ridiculous.

Gall, with his colleague Johann Spurzheim (1776–1832), identified thirty-seven “mental and moral faculties” which they thought were represented on the exterior surface of the skull. These faculties were divided into several spheres, such as intellect, perceptiveness, mental energy and love. Most of the faculties dealt with abstract personality traits such as firmness, cautiousness, marvellousness and spirituality. A chart of the skull was developed, mapping the regions where the bumps and depressions related to these traits could be palpated, measured and diagnosed. White porcelain heads with these maps drawn on them are ubiquitous in antique shops around the world.

Phrenology was widely taken up in general practice. Inevitably, however, it was challenged, particularly by the French scientist Georges Cuvier (1769–1832). Gall himself was hounded out of Vienna by religious and political forces, only to settle in France. It is said that one of the final nails in the coffin of phrenology came when Gall’s interpretation of Napoleon Bonaparte’s skull failed to recognize all the noble qualities the French dictator possessed. Phrenology had all but died as a generally accepted concept by the end of the nineteenth century, though the British psychiatrist Bernard Hollander (1864–1934) persisted with the idea and the British Phrenological Society was listed until the late 1960s. Indeed phrases still used today, such as “you need your head read” and “high-brow” have their basis in phrenology.

Illuminating times – the nineteenth century scientists

This brings us to the nineteenth century and a hyperbolic increase in knowledge. For a physician, to have been alive during these times must have been extremely exciting. There were many players but only a few names have withstood the test of time.

Marie Jean Pierre Flourens (1794–1867), a French physiologist, began experiments to investigate the validity of Gall’s ideas. He selectively destroyed various parts of the brains of animals and stimulated both animal and human brains with electricity. He also carried out post-mortem studies of the brains of patients with significant mental or neurological deficits. When Flourens removed the two main halves, or hemispheres, of the brains of animals, he noted that all “perceptions and judgement” were abolished. This led him to the correct conclusion that the cerebral hemispheres contained the higher cognitive functions. He also removed the small, separate, ridged structure at the back of and below the cerebral hemispheres – the cerebellum (see chapter 5 – Anatomy) – which resulted in the loss of the animal’s co-ordination. Finally, noting death as a result of destruction of the lower part of the brainstem (termed the medulla oblongata, which emerges at the base of the brain and is connected to the spinal cord), he deduced that vital functions such as breathing and circulation were regulated there.

Flourens’s use of small animal brains did not provide information on the detailed localization of human functions but it was becoming possible to electrically stimulate the brain precisely and experiments could now involve the larger brains of primates and dogs. Enter Paul Pierre Broca (1824–1880), a French surgeon and anthropologist of enormous intellect, whose classic experiments with patients with severe deficits of speech led to the localization of language to a region on the left side towards the front of the brain. One of his patients could only say the word “tan” (and was called Tan by the staff as a result). After his death, Broca discovered a small area of the left side of his brain had been destroyed by syphilis. This region is now called Broca’s area.

A British neurologist, John Hughlings Jackson (1835–1911), later developed the idea of Broca’s area as the seat of language output, or expression. More or less simultaneously, the German neurologist Carl Wernicke (1848–1904) found a related area further back on the left, concerned with the understanding of language and, moreover, connected to Broca’s area by nerve fibre pathways. Thus the basis for our modern and even now still evolving, model of language was born (see chapter 14 – Language, hearing and music).

Two German physiologists, Gustav Fritsch (1838–1927) and Eduard Hitzig (1838–1907), began, through electrical stimulation of dog brains, to ma...

Table of contents

• Cover
• Title Page
• Copyright
• Contents
• Preface
• Acknowledgements
• List of plates
• Section 1: Introducing the brain
• Section 2: Making a brain and mind from one cell
• Section 3: Having and using a brain as an adult
• Appendix: Eric Chudler’s brain facts and figures
• Glossary
• Further reading
• Index