Part 1 begins with a discussion of trepanation or trephining (the "Hole in the Head" of the title). The operation was carried out as early as the late Palaeolithic and the patients often survived for long periods, as evidenced by healing of the bone margins. It was used in many parts of the world in historical times and is still practised today. It is even advocated on the internet as a do-it-yourself method of gaining spiritual enlightenment!
Ancient systems of medicine were divided on the question whether the brain or the heart was the organ of mind. Gradually the importance of the brain came to be widely recognised, partly as a result of unpleasant vivisection experiments on animals and even on humans. The Greek/Roman physician Galen was particularly prominent in gaining this recognition for the brain.
Another basic scientific question that took a long time to resolve concerned vision. Did this depend on rays leaving the eye or on light entering it? The notion that something leaves the eye is the basis of the very widespread belief in the evil eye. But even when the receptive nature of vision was recognised the important structure was at first thought to be the lens not the retina.
Even when the brain was understood to be the seat of mental processes there was still disagreement about the importance of its outermost part, the cerebral cortex. This was long thought to be of no importance - merely the "rind" on the outside. A remarkable anticipation of the functions of the cortex occurred in an unlikely place: the early eighteenth-century writing of the Swedish mystic Emanuel Swedenborg. But his ideas were totally ignored in his own time and indeed are little known even today. The role of the motor cortex in movement was not recognised by scientists in general until the nineteenth century.
The section on neuroscience and art includes an interesting discussion of how the brain processes left and right. This is a difficult task for children and even some adults and it may play a part in dyslexia, where mirror-image letters such as b and d are often confused. Gross suggests that there may be an evolutionary reason for this: in nature it is seldom important to distinguish between mirror images so our brains have not evolved to do so; it is a skill that has to be acquired.
In the Netherlands in the sixteenth century public dissections of criminals were staged as elaborate rituals. Gross discusses the reasons for these performances, which Rembrandt depicted on two occasions. They were by no means entirely educational or scientific but were important civic ceremonies. In a nicely phrased piece of understated irony Gross writes that today the equivalent of the "anatomy lesson" is the group photograph. "The lay functions of the public dissection, namely entertainment, voyeurism, and education, are largely carried out by television."
Part 3 starts by considering Claude Bernard, probably the most important scientist in the modern history of physiology. He achieved great renown in his own lifetime, but his most important idea, that of the stability of the internal environment (milieu intérieur) was not appreciated for more than 50 years after its formulation. Although Gross does not mention it, I was reminded of Charles Darwin, whose central notion of natural selection did not attain widespread scientific recognition until the twentieth century.
When I was a medical student in the 1950s we were told unequivocally that no new neurons form in the brain after, at the latest, early childhood. In fact research indicating the contrary was published by Joseph Altman in the early 1960s but it was almost entirely ignored. Other workers confirmed this finding later in birds but the dogma of "no neurogenesis in the adult brain" continued to be taught for mammals. Only in the 1990s did new techniques show conclusively that neurogenesis does occur in the adult mammalian brain.
Even so, the initial studies were only on the hippocampus and the olfactory bulb. There was still resistance to the notion that new neurons could form in the cortex. Gross thinks that this was because of technical difficulties and other reasons. He is certain that neurogenesis does occur in the mammalian cortex and that it has important consequences.
Other chapters in this section look at Bartolomeo Panizza's work on the visual brain and Donald R. Griffin's work on echolocation in bats. Griffin also studied animal consciousness, which in the behaviourist era was regarded as a non-subject.
The concluding chapter is about the "grandmother cell", which is a research subject that Gross himself has been active in. The idea is that there may be individual brain cells that respond selectively to particular sensory inputs, such as your grandmother's face. The term "grandmother cell" was first coined in 1969 by Jerry Lettvin, although the idea had been put forward independently a few years earlier by Jerzy Konorsky, who postulated "gnostic cells". At least in monkeys these highly selective cells seem to be concerned principally with the recognition of faces rather than other items, such as bananas, that might be thought to be important for the animals.
Although "grandmother cell" implies a single neuron that responds to a particular input it seems more likely that it is restricted groups of neurons that act in this way.
This a fairly technical book with plenty of diagrams and notes, as one might expect in view of the fact that it consists of reprinted papers. Readers who enjoyed Gross's previous book will probably want to read this one, and it provides interesting facts, but it repeats a good deal of what I had read earlier and I found it something of a pot-boiler.