Gross is an experimental neuroscientist specializing in vision. While he was completing his Ph.D thesis in 1960 he became interested in the history of the subject and has continued to write about it since then. The book covers a wide span of time and space, beginning with ancient Egypt. But Chinese medicine hardly comes into the story since the role of the brain was not recognized in China until the idea was introduced by a Jesuit in 1595.
In the early dynastic period in Egypt physicians made rational and empirical observations of the effects of brain injury, but in the Middle Kingdom, from about 2000 BCE, there was a trend towards mystical and religious speculation. But at all times in Egypt the heart was accorded more importance than the brain, a bias that continued to be felt for many centuries afterwards in other cultures.
Early Greek medicine, in the form of the Hippocratic tradition, recognized that epilepsy was a brain disorder. Gross notes, in passing, that the so-called Hippocratic oath seems to have derived from a later secret neopythagorean sect unconnected with the Hippocratic school. Plato was hostile to science, unlike Aristotle, but Aristotle, like the ancient Egyptians, believed that the heart and not the brain was the seat of sensation. He did recognize that the brain was an essential organ but thought that its function was to cool the heart. His authority had a baneful influence on subsequent scientific thought for many subsequent centuries.
Aristotle did not carry out dissection of human bodies, but anatomists in Alexandria did. So did the Roman historian of medicine, Celsus; in fact, he went further and advocated the vivisection of criminals, a practice he thought defensible because of the benefits it could provide for the innocent. But the most important ancient medical authority was Galen, who recognized the importance of the brain and demonstrated that the recurrent laryngeal nerve in the pig controlled its ability to squeal.
During the Middle Ages neuroscience largely disappeared from view in Europe; it reappears with the anatomical work of Vesalius in the sixteenth century. However, for a long time almost everyone thought that the convolutions of the cerebral cortex were quite unimportant; they were constantly drawn inaccurately, being pictured as if they resembled the folds of the small intestine. A notable exception to this dismissal of the cortex came from, of all people, the mystic Emanuel Swedenborg, who in the early eighteenth century arrived at an amazing set of prescient ideas on the importance of the cerebral cortex in sensation, cognition, and movement; but, for reasons that Gross discusses in a separate chapter, Swedenborg's writings on the brain were wholly ignored.
In the eighteenth century Franz Joseph Gall introduced the idea of cerebral localization, and in so doing gave birth to phrenology. In most people's minds this is synonymous with quackery, but in fact Gall got a lot of things right. The supposed correlations between skull and brain morphology were quickly discounted by scientists, but as late as the mid-nineteenth century the eminent anatomist Paul Broca was able to say that Gall's work was 'the starting point for every discovery in cerebral physiology in our century'.
Another example of a perhaps unlikely influence is that of Herbert Spencer, the largely self-educated philosopher who adopted Darwinism so enthusiastically and who provided the crucial inspiration for John Hughlings Jackson, generally regarded as the father of English neurology and the eponymous describer of the Jacksonian fit; among the patients with epilepsy that he studied was his own wife.
Recognition of the role of the cerebral cortex came late. For a long time the cortex was not thought to have any sensory function but was regarded purely as the seat of intellect. Views began to change as the result of studies in which experimental lesions were made in the visual cortex of monkeys. However, not until the second half of the twentieth century was it realized that areas of the brain outside the striate cortex were involved in vision.
As well as tracing the main story of how our understanding of the brain has evolved, Gross explores some fascinating byways. Swedenborg's contribution has already been noted. Gross also looks at Leonardo da Vinci's anatomical studies, which began quite fancifully with little attempt at accurate depiction but became more accurate as time went by.
A longer chapter traces the curious story of the hippocampus minor. The hippocampus (formerly called the hippocampus major) is an important structure in the floor of the temporal horn of the lateral ventricle, and is now known to have a vital role in the formation of memory. The term hippocampus minor no longer figures in modern neuroanatomical texts but it was formerly applied to a ridge in the floor of the posterior horn of the lateral ventricle caused by the deep inward penetration of the calcarine fissure. This was confusing enough, but in a farcical turn of events one author in 1779 substituted hippopotamus for hippocampus and this error was adopted by several others before someone spotted it. In the nineteenth century the hippocampus minor was thought to be an important marker for human intelligence and a vast amount of sterile controversy took place between Thomas Huxley and his arch-rival Richard Owen on the question of whether this structure did or did not exist in the brains of monkeys.
One theme that emerges very clearly from this book is the remarkable way in which accurate scientific observations are often neglected for long periods, sometimes hundreds of years. To take just one example among many: Thomas Willis in the seventeenth century carried out dissections and animal experiments, from which he concluded that the cortex of the brain was responsible for memory and will. He also said that the cortex initiates voluntary movement whereas the cerebellum is involved only in involuntary movement. Yet although Willis was a major figure in his day, his ideas fell out of favour for 150 years, and the cortex long continued to be regarded as a glandular, vascular, or protective rind of the brain.
Gross writes well and the book is very readable. Much of the information it provides was new to me. It will interest neurologists and neuroscientists but will also appeal to general readers who are attracted by the history of science.