Soul Made Flesh: Thomas Willis, the Discovery of the Brain and How It Changed the World
We live, the science writer Carl Zimmer tells us in this engagingly written book, in a "neurocentric age". Ask anyone raised in modern western society where their self, their personhood, is situated, and they will unhesitatingly locate it a little behind their eyes. Few neuroscientists would disagree, or doubt the propositions that the mind is the brain, the brain is the mind. But it was not always so, and relics of this past can be found in everyday speech and customs. On Valentine's Day we exchange hearts, not hypothalami, and in distress we grieve from the heart, not the amygdala, all because Greek, along with Chinese, medicine placed the heart at the centre of the self. But football fans whose team loses a match are gutted, and our everyday insights are gut feelings, because the Egyptians and the Hebrews lowered their sights from the heart to the bowels. Aristotle neatly combined the lot by providing us with three sorts of soul, located conveniently in bowels, heart and head, enabling that separation of lust (gut) and emotion (heart) from rationality (head) that has so plagued western philosophy ever since.
So how did we become neurocentric? And why, when neurocentrism seems so self-evident to us, did it take so long for it to triumph? Zimmer locates the transition from heart to brain in mid-17th-century Oxford, and above all to the insights of a short, stammering physician with hair "like a dark red pigge". And as for the delay, it is primarily down to the first-century Greek physician Galen, whose mistaken anatomy and physiology were received as gospel truths for the succeeding 14 centuries. Over this entire period, professors presided over dissections, reciting Galenic truths from the textbooks to their assembled students in flagrant contradiction of the evidence being carved out in front of them. The theatre of such events, long preceding Gunther von Hagens's plastinated displays, is memorably caught in Rembrandt's paintings of anatomy lessons.
Even when the importance of the brain began to be recognised, artists and philosophers alike focused their attention not on the soft greyish "bowl of curds" that we now see as housing its hundred billion nerve cells and their hundred trillion connections, but on the fluid-filled spaces of the brain's interior, the ventricles. Leonardo impregnated them with wax, stripped away the surrounding tissue and superbly illustrated their shape. Descartes saw them as the source of the hydraulic fluids that powered the nerves. Deciding, on somewhat dubious grounds, that the tiny pineal gland deep in the brain was the seat of the soul, the contact point between mind and matter, God and Man, he noted that the fluid from the ventricles washed its sides, and hence could act as a two-way transmission medium between soul and flesh.
To move forward, what was needed was a conceptual flip, to turn the brain inside out, recognise the "bowl of curds" as the home of thinking stuff and the fluid of the vesicles as merely the repository for its waste - not so obvious at a time before microscopes made it possible to see structure, cells and nerves within the brain-goo. This, Zimmer claims, was the achievement of the group of virtuosi - highly talented polymaths -more or less trapped in Oxford during the civil war and the Cromwellian republic of the mid-17th century. The group, inspired by the physician William Harvey, discoverer of the circulation of the blood and the role of the heart, included Christopher Wren in his pre-architect days, Robert Boyle, Irish aristocrat and formulator of the laws relating to pressure and temperature of gases, and Robert Hooke, who first used the term "cell" to describe the biological equivalents of atoms. And, central among them, was the upwardly mobile son of a local farmer, Thomas Willis.
With the restoration of the monarchy, many of this group would relocate to London and establish the Royal Society as Britain's first scientific academy. Yet this was before the days of scientific specialisations, of the fragmentation of culture and the location of "science" on the far side of the snow-line. The interests of the virtuosi ranged across the entire terrain of the natural and social sciences, from physics and physiology to architecture and the arts. Wren's drawings of nerves illustrate Willis's textbook (and are reproduced by Zimmer). William Petty began as a physician and ended as a pioneer social statistician. Keen natural observers, they also invented a new technique for acquiring knowledge of the world - they experimented.
This, above all, is why Willis's dissecting rooms, across the road from Merton College, take centre stage in Zimmer's account. It is here that human corpses were dissected with increasing delicacy, that the great nerve tracts to and from the brain began to be mapped, and where Willis made the one discovery that formal accounts of the history of neuroanatomy recognise - the rich blood supply to the brain and the "circle of Willis" at the base of the brain, crucial to ensuring that supply. But it is also where the experimenters strapped living dogs to their dissecting table and opened them up to explore the beating of the heart, the effects of removing a variety of internal organs (some of which, astonishingly, the dogs survived) and the possibility of transfusing blood.
But nobody can entirely break the chains of the past. To transcend Galen, Willis turned to the writing of the mystical 16th-century alchemist Paracelsus and his successors. Where Galen approached life through anatomy, Paracelsus did so through chemistry. What was important to health in the Paracelsian tradition was the balance of chemicals in the body. So to the traditional medical approaches of bleeding sick patients nearly to death to rid them of undesirable "humours" Willis added unsavoury concoctions of semi-toxic metal salts. This seems greatly to have increased his fame as a physician after the Restoration, though it is puzzling to see why, as Zimmer cites no evidence of his medical successes and a fair number of distinct failures.
Although Willis is ostensibly Zimmer's central theme, the book ranges widely. Not only does he provide a good account of the state of medico-physiological knowledge during the post-Galenic period leading up to the birth of modern neuroscience, but Willis's own story becomes almost submerged in a racy history of the civil war, the Cromwellian revolution and the subsequent restoration of the monarchy. The great theological debates of the time provide the conceptual framework within which the new sciences were born, especially the Protestant (and above all Puritanical) refusal to accept the authority of the church's interpretation of scripture. Despite many of them being royalists, the virtuosi shared this scepticism, symbolised in the motto of the Royal Society - Nullius in verba .
Despite Willis's achievements, he remains today a relatively unknown figure, certainly by comparison with his great contemporaries. Zimmer argues that this is largely the fault of the man who was briefly Willis's pupil, the great John Locke. Willis was a materialist who saw in materialism the revelation of the works of God. The charge of atheism, thrown by the church at all who dared to confront scripture with empirical evidence or logical reason, was almost as serious a threat to livelihood, if not life, in the Protestant north of Europe as it was in the Catholic south, and the virtuosi picked their way carefully through this minefield. Locke, a generation later, felt free to discuss the mind and its functions without the need to refer either upward, to scriptural authority, or downward, to the materiality of the body. The English tradition of empiricist philosophy was born, creating a fresh severance between the studies of mind and of brain, which was to last virtually until the last couple of decades.
In his final chapter, Zimmer fast-forwards his story somewhat uncritically to the modern triumphs of (American) neuroscience, with its commitment to reducing the soul to nothing more than flesh powered by information theory. I suspect that the virtuosi, marvelling at the extraordinary windows into the brain provided by the latest imaging techniques, would nonetheless have resisted such a simplistic interpretation. I share that scepticism.