If I were to die later today before finishing this chapter and my brain was removed from my skull, it would weigh about 1,400 grams — roughly the same as a bag and a half of granulated sugar. Before being preserved for posterity by being marinated in a jar of formalin (better still, perhaps, strong alcohol with some flavouring), about 75 to 80 per cent of my brain would be made up of water, with just over 10 per cent fat and about 8 per cent protein. If, once it was fixed, people came to examine it and poke it about a bit, it would appear rather crinkled and whitish, and have the slightly rubbery consistency of a large mushroom. And what is more, if you, dear reader, were to die at the same time and have your brain treated in the same peremptory fashion, it would be so similar to mine that any difference would almost certainly be undetectable.
The chances are that no matter how closely our respective brains were viewed, there would be hardly anything obvious to show that what amused passers-by were gazing at were two totally different specimens of the most complicated structure on this planet. There would be nothing to reveal that these two rubbery objects, which to some bystanders would seem faintly disgusting, respectively comprised the sum total of our very being and personality. Nothing to show that at some time we had both loved in different ways, had known different pains, ambitions and disappointments, and had been angry and taken pleasure at different things. Nor that we had learnt different physical and intellectual skills, had mind-bending experiences in different parts of the world, had totally different memories, liked different food or music, and that each of us had quite different human strengths and failings.
Perhaps it is not so surprising then that it has taken humans such a long time to understand the complex nature of the brain, and that it is the very centre of what makes us who we are. Although surgical drilling of holes in the skull (for whatever now mysterious purpose) goes back to Cro-Magnon man some 40,000 years ago, and knowledge of the mind-altering nature of alcohol and the sap from the poppy plant is longstanding, most old civilizations regarded the heart, not the brain, as the centre of the soul. Ancient Egyptians, when embalming human bodies, religiously preserved the heart but destroyed the brain - because otherwise it would rot — by scraping it out of a hole they drilled in the bones at the back of the nose and palate. But it was an Egyptian surgeon who left the first written descriptions that give evidence of some basic insight into neuroscience.
The Edwin Smith Papyrus is one of the oldest known written documents. It is around 3,700 years old and is a surgical treatise describing injuries, mostly to the head, in forty-eight different patients. The Egyptologist, Edwin Smith, who first handled this extraordinary manuscript brought it back from Luxor in 1862, but he did not understand the remarkable nature of the text. Its real significance was recognized by James Breasted, director of the Chicago Oriental Institute, in 1930, who realized it was a scribe's copy of a treatise from an even earlier time - possibly some 5,000 years ago. The horrifying injuries of Case Number Six give a description of the pulsating brain under the surgeon's hands:
If thou examinest a man having a gaping wound in his head, penetrating to the bone and smashing his skull, and rending open the brain, thou shouldst palpate the wound. Shouldst thou find that smash which is in his skull those corrugations which form in molten copper, and something therein throbbing and fluttering under thy fingers — like the weak place in an infant's fontanelle before it becomes whole . . . then if he suffers blood from both his nostrils and stiffness in his neck . . . thou shouldst say concerning him 'An ailment not to be treated'. Thou shouldst anoint that wound with grease but not bind it; thou shalt not apply two strips upon it until thou knowest he has reached a decisive point.
So even Egyptian physicians knew when it might be more prudent not to treat a patient actively. These hieroglyphics go on to describe the delicate membranes lining the injured brain, the meninges, and the discharge of cerebrospinal fluid from inside the head. Elsewhere the papyrus records the symptoms of a patient unable to move one limb after severe head injuries on one side, and loss of speech resulting from injuries to the temple — presumably damage to the frontal lobe and Broca's area - several thousand years before Dr Paul Pierre Broca described the speech centre in the 1860s.
The mind/body debate
Thousands of years elapsed before the brain, rather than the heart, was universally recognized as the most important organ in the body. Alcmaeon, who around 500bc was one of the earliest to see the brain's importance, regarded it as the centre of sensation - he removed an animal's eye and noted the tracts leading to the brain, recording that 'all senses are connected to the brain'. Plato believed in the soul - the essence of ourselves, and what we might in modern times call the 'mind' - and he thought that it had a separate existence from the body, to the extent that it could survive after the body had expired. He believed that the centre of the intellect was in the head.
But Aristotle, who lived from 384 to 322bc, appears to have disagreed with his teacher, Plato. He seems to have regarded the heart as more important. All the lower animals he examined — worms, insects and shellfish — had a pulsating organ resembling a heart but they did not have an obvious brain. All blood vessels led towards the heart, and he describes how the heart twitched when touched while the brain of higher animals remained inert. The fact that a chicken ran about after its head was cut off helped Aristotle to the view that 'the seat of the soul and the control of voluntary movement - in fact of nervous functions in general - are to be sought in the heart. The brain is an organ of minor importance, perhaps necessary to cool the blood.' Aristotle hugely influenced the medieval scholars who came later; after all, his view of the importance of the heart fitted with biblical accounts. The notion of the heart as the centre of human behaviour survived until the sixteenth century. 'Faith sits under the left nipple,' said Martin Luther.
A little earlier than Aristotle, though, the philosopher Democritus argued against the heart being the centre of human functions. He writes: 'The brain watches over the upper limbs like a guard, as citadel of the body, consecrated to its protection,' and adds that 'the brain, guardian of thoughts or intelligence', contains the principal 'bonds of the soul'.
Hippocrates, the father of medical practice, recognized the unique nature of the brain: '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, grief 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 . . .'
In the third century BC, Herophilus and Erasistratus, both human anatomists, dissected thousands of bodies and demonstrated that nerves were different from blood vessels and that they originated not in the heart, as Aristotle thought, but in the brain or the spinal cord. Then, almost five hundred years after Herophilus' day, the Greek physician Galen (AD130-200) dissected pigs, cattle and monkeys and wrote meticulous accounts of what he had seen. By cutting various nerves, such as those coming from the spinal cord, he established the lack of function caused by their damage. He also demonstrated that severing the laryngeal nerve resulted in the loss of the ability to make noise. During his career he was a physician to gladiators in Rome. Seeing many head injuries presumably gave him an insight into the working of the nervous system and the understanding that the brain played a central role in controlling bodily and mental activity.
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