The Idea of the Brain

– ONE –

HEART

PREHISTORY TO 17TH CENTURY

The scientific consensus is that, in ways we do not understand, thought is produced by the activity of billions of cells in the most complex structure in the known universe–the human brain. Surprising as it may be, this focus on the brain seems to be a relatively recent development. Virtually all we know from prehistory and history suggests that for most of our past we have viewed the heart, not the brain, as the fundamental organ of thought and feeling. The power of these old, pre-scientific views can be seen in our everyday language–words and phrases like ‘learn by heart’, ‘heartbroken’, ‘heartfelt’, and so on (similar examples can be found in many other languages). These phrases still carry the emotional charge of the old world-view that we have supposedly discarded–try replacing the word ‘heart’ by ‘brain’ and see how it feels.

Our earliest written artefacts show the importance of this idea to past cultures. In the Epic of Gilgamesh, a 4,000-year-old story written in what is now Iraq, emotions and feelings were clearly based in the heart, while in the Indian Rigveda, a collection of Vedic Sanskrit hymns written around 3,200 years ago, the heart is the site of thought.¹ The Shabaka Stone, a shiny grey slab of basalt from ancient Egypt, now in the British Museum, is covered in hieroglyphs that describe a 3,000-year-old Egyptian myth focused on the importance of the heart in thinking.² The Old Testament reveals that at around the same time as the Shabaka Stone was carved, the Jews considered the heart to be the origin of thought in both humans and God.³

Heart-centred views also existed in the Americas, where the great empires of Central America–the Maya (250–900 CE) and the Aztecs (1400–1500 CE)–both focused on the heart as the source of emotions and thought. We also have some insight into the beliefs of those peoples from North and Central America who did not develop extensive urban cultures. In the early years of the twentieth century, US ethnographers worked with indigenous peoples, documenting their traditions and beliefs. Although we cannot be certain that the recorded views were typical of the cultures that existed before the arrival of Europeans, most of the peoples who contributed to these studies considered that something like a ‘life-soul’, or an emotional consciousness, was linked to the heart and to breath. This view was widespread, from Greenland to Nicaragua, and was held by peoples with ecologies as diverse as the Eskimo, the Coast Salish of the Pacific north-west, and the Hopi of Arizona.⁴

These views are remarkably congruent with the account of the Swiss psychoanalyst Carl Jung, who in the early decades of the twentieth century travelled to New Mexico. On the roof of one of the white adobe buildings built by the Pueblo people on the high Taos plateau, Jung talked with Ochwiay Biano of the Taos Pueblo. Biano told Jung that he did not understand white people, whom he considered cruel, uneasy and restless–‘We think that they are mad’, he said. Intrigued, Jung asked Biano why he thought this:

Not all cultures have shared this widespread focus on the heart. On the other side of the planet, a key aspect of the outlook of the Aboriginal and Torres Strait Islander peoples in Australia was (and is) their link with the land, which extends to ideas about mind and spirit. Locating the seat of thought within the body appears not to have been part of their world view.⁶ Similarly, traditional Chinese approaches to medicine and anatomy were primarily focused on the interactions of a series of forces, rather than localisation of function. However, when Chinese thinkers did seek to identify the roles of particular organs, the heart was the key.⁷ The Guanzi, a document originally written by the Chinese philosopher Guan Zhong in the seventh century BCE, argued that the heart was fundamental for all functions of the body, including the senses.

Heart-centred views correspond to our everyday experience–the heart changes its rhythm at the same time as our feelings change, while powerful emotions such as anger, lust or fear seem to be focused on one or more of our internal organs, and to course through our bodies and change our way of thinking as though they are transported in, or simply are, our blood. This is why those old phrases about being ‘down at heart’ and so on have persisted–they correspond to the way we perceive an important part of our inner life. Just as with the appearance that the sun goes around the earth, everyday experience of being human provided a simple explanation of where we think–our hearts. People believed this idea because it made sense.

Even though the heart was widely seen as the centre of our inner life, certain cultures recognised that the brain had some kind of function, even if this could only be detected through injury. For example, in ancient Egypt a number of scribes created a medical document known as the Edwin Smith Papyrus.⁸ The manuscript includes a brief description of the convolutions of the brain and the recognition that damage to one side of the head could be accompanied by paralysis on the opposite side of the body, but for these writers, as for all ancient Egyptians, the heart was nevertheless the seat of the soul and mental activity.

The first recorded challenge to our global heart-centred view occurred in ancient Greece. In the space of about three and a half centuries, between 600 and 250 BCE, Greek philosophers shaped the way that the modern world views so many things, including the brain. The early Greeks, like other peoples, considered that the heart was the origin of feelings and thought. This can be seen in the epic oral poems now attributed to Homer, which were created sometime between the twelfth and eighth centuries BCE; similarly, the ideas of the earliest recorded philosophers were focused on the heart.⁹ In the fifth century BCE the philosopher Alcmaeon took issue with this view. Alcmaeon lived in Croton, a Greek town in the ‘foot’ of Italy, and is sometimes presented as a physician and as the father of neuroscience, although everything we know of him and his work is hearsay. None of his writings survive–all that remain are fragments quoted by later thinkers.

Alcmaeon was interested in the senses, and this naturally led him to focus on the head, where the key sense organs are grouped. According to subsequent writers, Alcmaeon showed that the eyes, and by extension the other sense organs, were connected to the brain by what he called narrow tubes. Aetius, living 300 years after Alcmaeon, is reported as having said that, for Alcmaeon, ‘the governing facility of intelligence is the brain’. It is not clear how exactly Alcmaeon arrived at this conclusion–subsequent writers imply that he based his ideas not simply on introspection and philosophical musings, but also on direct investigation, although there is no evidence of this. He may have dissected an eyeball (not necessarily a human one) or he may have witnessed the culinary preparation of an animal’s head, or he may simply have used his fingers to see how the eyes, tongue and nose were connected to the inner parts of an animal’s skull.¹⁰

Despite these insights, the earliest unambiguous statements about the centrality of the brain were written several decades after Alcmaeon died; they came from the school of medicine on the island of Kos, whose most famous member was Hippocrates. Many of the works produced by the Kos school of medicine are attributed to Hippocrates, although the actual authors are unknown. One of the most significant of these documents was On the Sacred Disease, which was written around 400 BCE for a non-specialist audience and dealt with epilepsy (why epilepsy was considered a sacred or divine disease is unclear¹¹). According to the author(s):

The argument in On the Sacred Disease was based partly on some pioneering but rudimentary anatomy (‘the brain of man, as in all other animals, is double, and a thin membrane divides it through the middle’, the author(s) stated), but it also revealed a great deal of confusion. For example, the document claimed that ‘when a person draws in air by the mouth and nostrils, the breath goes first to the brain’, arguing that the veins transport air around the body. Epilepsy was explained by the idea that a humour or fluid called phlegm entered the veins, preventing the air from getting to the brain and so causing the fit. Some people took the implications of localising epilepsy to the brain very seriously. Aretaeus the Cappadocian, a Greek physician who lived around 150 BCE, treated it by trepanation–drilling holes in the skull–a tradition that lived on in European medical manuals until the eighteenth century.¹³ Aretaeus did not invent this operation–the earliest traces of any medical intervention are holes that were drilled or scraped into people’s skulls and which can be found all over the planet, sometimes from over 10,000 years ago.¹⁴ Although it is tempting to view prehistoric trepanation as an early form of psychosurgery (it is often suggested that trepanation was performed to let out ‘evil spirits’), the global dominance of heart-centred ideas about the origins of thought suggests this is unlikely. There are more credible justifications for such a dangerous operation, including relief of painful subcranial bleeding or removal of bone fragments following a head injury.

Despite the arguments of Alcmaeon and of the Kos school, in the absence of any evidence to prove that the brain is the site of thought and emotion, there was no reason to prefer this claim to the obvious explanation that the heart plays this role. This led one of the most influential Greek philosophers, Aristotle, to dismiss the idea that the brain played any significant part in thinking or movement. As he wrote in Parts of Animals:

Aristotle’s argument for the centrality of the heart was based on apparently self-evident principles, such as the link between movement, heat and thought. Aristotle noted that the heart clearly changed its activity at the same time as emotions were felt, whereas the brain apparently did nothing; he also affirmed that the heart was the source of blood, which is necessary for sensation, while the brain contained no blood of its own. Furthermore, all large animals have a heart, whereas–he claimed–only the higher animals have a brain. His final argument was that the heart is warm and shows movement, both of which were seen as essential features of life; in contrast, the brain is immobile and cold.¹⁵ Given there was no actual proof of any link between thought and the brain, Aristotle’s logical arguments were just as valid as those to be found in the writings of the Kos school. There was no way to choose between them. Elsewhere around the planet, things continued as before: for the vast majority of people, the heart was what counted.

After Aristotle’s death, insight into the role of the brain emerged from Alexandria, at the western edge of the Nile Delta, in Greek-ruled Egypt. With a grid system of streets, underground plumbing and a multicultural population, Alexandria was one of the most significant centres of the Graeco-Roman world. Among those who benefited from this fertile intellectual atmosphere were the two leading Greek anatomists of the period, Herophilus of Chalcedon and Erasistratus of Ceos, both of whom worked in Alexandria.¹⁶

None of the writings of Herophilus and Erasistratus have survived, but subsequent writers claimed that they made important discoveries in the structure of the brain. The reason these breakthroughs came about in Alexandria was that, for a brief period, and apparently for the first time in history, the dissection of human bodies was permitted. It is even said that criminals who were condemned to death were vivisected under what must have been appalling circumstances. Exactly why dissection was allowed in Alexandria but not elsewhere is unclear, but whatever the case, physicians in the city made substantial anatomical advances relating to the liver, the eye and the circulatory system. They even described the heart as a pump.

The direct study of human anatomy enabled Herophilus and Erasistratus to make significant discoveries with regard to the brain and the nervous system. Herophilus supposedly described the anatomy of two key parts of the human brain–the cortex (the two large lobes of the brain), and the cerebellum, at the back of the brain, which he considered to be the seat of intelligence–as well as showing the origin of the spinal cord and how the nerves branch. He is said to have distinguished between nerves that were linked to the sense organs and the motor nerves that guide behaviour, developing a theory of sensation in which the optic nerve was hollow and some kind of air moved through this space.¹⁷ Erasistratus apparently took a different approach, comparing the human brain with the brains of stags and hares, concluding that the greater complexity of the human brain, as shown by its convolutions, was responsible for our greater intelligence.

Despite the accuracy of their descriptions, the work of Herophilus and Erasistratus did not settle the issue of whether the heart or the brain is the site of thought and feeling. They merely showed that the brain was complicated. Aristotle’s heart-centred view remained enormously influential, partly because of his immense prestige, but above all because it corresponded to everyday experience.

It was another 400 years before decisive evidence about the role of the brain was obtained, through the work of one of the most influential thinkers in the history of Western civilisation: Galen. A Roman citizen, Galen was born in 129 CE to a wealthy family in the city of Pergamon in what is now western Turkey.¹⁸ Although today Galen is principally known as a writer on medical matters–his ideas shaped Western medicine and culture for 1,500 years–he was in fact one of the major thinkers of the late Roman world, producing millions of words of philosophy, poetry and prose.¹⁹

Galen travelled and studied throughout the eastern Mediterranean, including Alexandria, but the key years of his life were spent in Rome. He arrived there in 162 CE, aged thirty-two, following a four-year stint as physician to the gladiators in Pergamon, during which time he learned much about the human body by treating the fighters’ wounds. He soon became a fashionable Roman physician, attending some of the leading figures in the city, including Emperor Marcus Aurelius, and gaining a reputation as a brilliant anatomist who had a taste for polemical argument. To demonstrate his discoveries Galen used ‘lecture-commentaries’ in which he simultaneously described his new knowledge and showed it in an animal. In these lectures the audience was invited to witness Galen’s performance, and thereby to validate his claims–this was part of Galen’s emphasis on the importance of experience in understanding. (The following explanation of how Galen came to some of his conclusions is rather grisly. If you are squeamish, you might prefer to skip the next three paragraphs.)

One of the key issues that interested Galen was the role of the brain and the location of thought and the soul–he was convinced that the brain was fundamental to behaviour and thought, and that he could prove it by experimentation on animals. All this at a time where there were no anaesthetics. Galen was not immune to the horror that he was inflicting–he counselled against using monkeys as their facial expressions during the experiment were too disturbing. Although Galen disagreed with those who argued that animals lacked part of the soul relating to anger and desire, he said nothing about pain–pain is not to be found in his descriptions of his work.²⁰

One of Galen’s most decisive experiments focused on the role of the nerves in the production of the voice; this was done on a pig because ‘the animal that squeals the loudest is the most convenient for experiments in which the voice is harmed’.²¹ With the poor pig strapped down on its back, its muzzle bound tightly shut, Galen cut into the flesh and revealed the recurrent laryngeal nerves that run either side of the carotid artery in the neck. If he tied a thread tightly round the nerves, the muffled squealing of the animal ceased; if he loosened the ligature, the voice would return. Although squealing was clearly produced by the larynx, something appeared to be moving down the nerves from the brain.

This insight was reinforced by one of Galen’s most remarkable demonstrations, in which he proved the importance of the brain by directly confronting opponents with the implications of their heart-centred views. Having cut open a living animal, Galen obliged his contradictor to squeeze the beast’s heart and prevent it from beating. Even with the heart stopped, the poor animal continued its muted whimpers, showing that the movement of the heart was not necessary for the animal to make sounds. But when Galen opened the skull and made his rival press on the brain, the animal immediately stopped making a noise and became unconscious. When the pressure was released, Galen reported, ‘the animal returns to consciousness and can move again’. This must have been quite astonishing for the audience. As the historian Maud Gleason has put it, ‘Galen’s anatomical performances look less and less like an intellectual debate and more like a magic show.’²²

On the basis of this evidence–supported by many other anatomical descriptions and surgical interventions, including on patients–Galen became certain that the brain was the centre of thought. He argued that the brain produced a special kind of air or pneuma that leaked out if the brain was injured, producing unconsciousness; when enough of this air accumulated, consciousness returned. Movement of the body was a consequence of the air produced by the brain moving down the apparently hollow nerves, Galen said. His anatomical work–most of it done on animals rather than on humans–showed that all nerves came from the brain, not the heart as Aristotle had claimed.

Despite the evidence that Galen presented, the authority of thinkers such as Aristotle and the power of everyday experience prevented brain-centred views from driving out the old ideas, even in Rome. Galen left an immense volume of work–around 400 treatises, of which over 170 survive, covering the whole range of medicine and natural science–but the decline and fall of the Roman Empire led to a collapse of the intellectual environment that could have permitted further discoveries. Simply thinking about where thought came from would never resolve the issue–as Galen’s work indicated, it would require anatomical and experimental investigation, which in turn could occur only in a context of intellectual openness and knowledge of past successes and failures through the circulation of ideas. Those conditions would not be repeated for centuries.

Much of the cultural heritage of Rome and Greece was preserved in the libraries of the eastern Roman Empire, centred on Byzantium (modern-day Istanbul). From the seventh century onwards, the appearance of various caliphates associated with the rise of Islam led to a culture that spread to France in the west, to Bulgaria in the north and to Turkmenistan and Afghanistan in the east. This Islamic society placed a high value on knowledge and technical skills, and to meet the appetites of the new dominant classes and ruling groups, bridges and canals were constructed, horoscopes were cast, paper and glass were made. All this required rediscovering old wisdom or developing new understanding.²³

First there was a wave of translations of the Greek and Roman texts that could be found in Persian or Byzantine libraries–this trend was centred on Baghdad and was sponsored by the caliphs and rich merchants. The ideas in these documents were soon extended as thinkers developed whole new areas of knowledge such as algebra, astronomy, optics and chemistry. But medicine and anatomy remained firmly anchored in Greek and Roman views, tied to the texts that were translated. In particular, the arguments about the roles of the heart and the brain that had existed since the time of Aristotle and Hippocrates were transmitted down the centuries more or less intact.

One of the leading physicians and philosophers of this period was Ibn-Sīnā, known in the West as Avicenna. Born in what is now Uzbekistan in 980, Avicenna lived in what is now Iran and wrote hundreds of books. His work combined Greek and Arabic thinking as well as treatments and diagnoses from as far afield as India; translated into Latin in the twelfth century, it exerted a profound influence on Western medicine for 500 years. Avicenna accepted Galen’s claim that nerves arise from the brain or the spinal cord, but insisted, like Aristotle, that the primary source of all movement and sensation was nevertheless the heart.²⁴ This view also fitted with the Qur’an, which often refers to the heart as the source of understanding and, like the Bible, contains no mention of the brain at all.

Another route by which Galen’s ideas were transmitted during this period was through the work of the tenth-century physician ‘Alī ibn al-’Abbās Maǧūsī, known in the West as Haly Abbas–a historian has described him as ‘a Persian who took an Arab name and wrote in the language of the Qu’ran, a Zoroastrian who was imbibed with Greek traditions, a thinker from the Islamic world who was adopted by the Western Latin community less than a century after his death’.To emphasise the cosmopolitan mix of this period, his work was subsequently translated into Latin in Italy by a Christian monk who had been a Muslim refugee from North Africa.²⁵

Among the writings of Galen that Haly Abbas translated were those covering the structure and the role of the brain: ‘The brain is the principal organ of the psychical members. For within the brain is seated memory, reason and intellect, and from the brain is distributed the power, sensation and voluntary motion.’²⁶

Haly Abbas also put forward an idea that was not present in Galen–he claimed that the three cavities or ventricles in the brain were full of animal spirits^* that were created in the heart and transported in the blood. Each of the ventricles, he said, had a different psychological function: ‘Animal spirit in the anterior ventricles creates sensation and imagination, animal spirit in the middle ventricle becomes intellect or reason, and animal spirit transmitted to the posterior ventricle produces motion and memory.’

Despite the lack of evidence for this idea, it was widely held throughout Europe and the Middle East for over a millennium.²⁷ It had first appeared in the writings of the fourth-century Bishop Nemesius of Emesa in Syria, and a few decades later was briefly mentioned by Saint Augustine, thereby acquiring a patina of religious approval that helped maintain its popularity.²⁸ For over 1,200 years, ventricular localisation was widely accepted as self-evident–between the fourth and sixteenth centuries, at least twenty-four different versions were put forward.²⁹