When the brain was named king

We live in what Carl Zimmer, one of our most gifted science writers, calls a Neurocentric Age, in which the physical workings of the brain are seen as inextricably linked to reason, emotion, language, morality and mental illness. How we came to that realization, which Zimmer describes in his fascinating book, “Soul Made Flesh,” amounted to a kind of second Copernican revolution -- one inside the body.

The thrilling story Zimmer tells begins 350 years ago in Oxford, a town that in the 17th century was to science what 15th century Florence had been to art: a smallish provincial city from which a clutch of trailblazing geniuses suddenly burst out of the blue. If Florence produced Brunelleschi, Ghiberti and Donatello in the span of a single generation, Oxford created its own renaissance in the 1650s through the efforts of the Oxford Experimental Philosophy Club, a group that came together on Thursday afternoons to debunk age-old textbooks by performing wide-ranging -- and often grisly -- experiments. Members included Robert Boyle, Robert Hooke and a young prodigy named Christopher Wren, who was at the time more celebrated for operating on dogs than for building churches. Also present at these sessions was a short, stammering and rather charmless red-haired country doctor named Thomas Willis. His contributions to the Oxford Experimental Philosophy Club were as pioneering as they were gruesome: “I addicted myself to the opening of heads,” he later recalled, with typical sangfroid, of his groundbreaking studies of the human brain.

Willis is the subject of Zimmer’s book, which seeks to rescue him from the relative obscurity into which he has faded despite far-reaching influences as the father of neuroscience and the author of the founding text on the anatomy of the central nervous system. Willis is too easily lost in the glare of other heroes of the 17th century’s scientific revolution, such as Galileo, Harvey and Newton. But Zimmer makes a convincing case that Willis is just as pivotal a figure in the history of Western thought, having recognized that emotions and many illnesses were products of the brain, at a time when more often than not they were considered the work of comets or demons.

Despite his achievements, Willis is in many ways, as Zimmer shows, an improbable scientific hero. Unlike so many of his brilliant colleagues, he matured slowly, serving a long and obscure medical apprenticeship before launching himself on the world. After acquiring a medical degree from Oxford University in 1646, he spent more than a decade as a “pisse-prophet,” inspecting the color of his patients’ urine and prescribing time-honored but highly dubious remedies, such as ground-up millipedes, amulets of mistletoe and roasted apples stuffed with frankincense. Zimmer suggests that Willis would have turned into just another quack doctor had he not fallen under the spell of an enterprising young physician named William Petty, who arrived in Oxford in 1649 after studies in Leiden and Paris. Holding to the latest Parisian theory that the body was a mechanical contraption, Petty ignored the official medical textbooks and, with Willis at his side, began cutting open the cadavers of executed criminals to peer at their inner workings.

Armed with a new knowledge of anatomy, Willis ambitiously turned his attentions to the brain, hoping to, as he put it, “unlock the secret places of man’s mind.” The brain, as Zimmer shows, was still quite low in the hierarchy of body parts when Willis began opening heads. Taking their cue from Aristotle, who had situated the soul in the heart rather than the head, most writers believed the brain to be little more than, as the philosopher Henry More wrote in 1653, a “bowl of curds.” Reason, will and passion were all assigned to more philosophically esteemed organs, such as the heart or the liver.

Occasional attempts had been made to give the brain its due: Galen had located the rational soul in the ventricles of the brain, Descartes in the pineal gland. But such hypotheses were undermined by the fact that neither Galen nor Descartes had ever actually dissected a human brain. Those who had done so -- such as Andreas Vesalius in the middle of the 16th century -- were plagued by both primitive techniques (Vesalius clumsily sawed slices off the top of the head as the brain steadily rotted) and very real anxieties that attempts to plant the soul in the inert-looking gray matter of the brain might be denounced as heretical.

Willis managed to clear these hurdles. Zimmer’s nimble survey of the intellectual landscape of the 17th century reveals just how deeply his studies were influenced by both the scientific and political communities of which he was a part. Boyle’s discovery that putrefaction could be halted by immersing organs in pure alcohol meant that Willis was able to preserve brains for as long as he wished, carving them up and studying them at his leisure, even making use of microscopes designed by Wren and Hooke. He was the beneficiary of numerous other recent scientific advances, including William Harvey’s treatise on the circulation of the blood and Wren’s innovative technique of intravenous injection. The fruit of Willis’ labors was his 1664 work “Cerebri anatome,” a landmark in the history of science that Zimmer claims has become part of the “bedrock of modern Western thought.”

Through dissection and careful observation, he recognized that the brain communicated back and forth with the muscles and organs, receiving signals and giving commands via a complex network of nerves. This realization had far-reaching consequences, and not just for anatomy. By demonstrating how the cerebellum controlled the beating of the heart through a network of nerves running down the spinal column, Willis proved for the first time that the brain, not the heart, was the primum mobile. Or, as Zimmer puts it, “the heart was no longer the king of the body. Willis handed that title to the brain.” The clues to human intellect, passion and memory could be found, therefore, by anatomizing the brain.

Such a perception, a few years earlier, would have landed Willis in trouble.

As Zimmer notes, Vesalius had stopped short in his speculations about the powers of the brain “lest I come into collision with some scandalmonger or censor of heresy.” Willis, however, prudently declined to banish the soul from his map of the brain. He was careful to wed his new science to an old theology, eluding charges of materialism by stressing that although the rational soul was located in the gray matter of the brain -- specifically, in the corpus callosum -- it survived the death and decomposition of its host.

This foray into theological matters notwithstanding, Willis’ interest in the brain was above all practical, as befitted a doctor. He spent the remainder of his life building up a lucrative medical practice in Oxford and studying the brain’s many diseases. He coined the word “neurology” to describe his new type of medicine and gave precise clinical descriptions of epilepsy, narcolepsy and migraines. If his cures still bordered on quackery (his lack of success in treating his patients seems to have ensured a steady stream of corpses for dissection), his overall diagnosis of the brain’s diseases was revealing. Most physical and mental ailments were, he maintained, the result of a “civil war” in the body -- a battle waged by the “lower” soul, or the bearer of sense impressions, against the rational soul housed in the corpus callosum. Zimmer shows how the studies of Willis, an ardent Royalist, constituted a search for scientific assurances in an age when England had been ravaged by war, regicide and sectarianism -- when the brutish subordinates had risen up to dethrone the ruling monarch and plunge the nation into chaos. Willis’ final conception of a healthy relationship between brain and body was thus, Zimmer notes, a nostalgic evocation of harmonious social relations in pre-Cromwell England: the rational soul seated on its throne in the corpus callosum, with the lower soul keeping to its place like an obedient servant.

“Soul Made Flesh” may not be for the fainthearted, with its accounts of repulsive diseases and their even more repulsive cures. We learn, for example, how holes were drilled into the heads of migraine sufferers, and how other patients were subjected to transfusions of lamb’s blood and remedies concocted from carved-up puppies. (One of the more uncongenial aspects of the Oxford Experimental Philosophy Club was its incredibly callous attitude toward animals.) But Zimmer has produced a top-notch work of popular science, chock-full of fascinating lore and inspired quotations.

Hosts of knotty concepts are treated to lucid descriptions, and his fluent prose and vivid narration prove themselves as much at home among the complex historical and political crosscurrents of the 17th century as they are with finely tuned accounts of biochemistry or MRI scanners.

In the end, Zimmer casts doubt on the obsessions of our Neurocentric Age, with its faith in the scientific ability to trace every decision or emotion to a chemical reaction in the brain and, by so doing, to banish from the mind-body equation the incorporeal soul that Willis had so scrupulously preserved. This materialism may have hit the buffers in any case. Zimmer claims that the images of the brain produced by today’s neuroscientists are, for all their sophistication, the equivalent of early mariners’ maps of unexplored continents. It’s comforting to know that there are still more things in heaven and earth than are dreamt of in scientific laboratories.