Brain, Vision, Memory

Charlie Gross is distinguished for his discovery of face-selective neurons in the temporal cortex of primates, which he wittily describes in the final chapter of this book. He found these at a time when a debate about the neuronal organisation of sensory processing raged. On one side, the 'hierarchicists' held that processing took place in layers of neurons that formed a pyramid-like structure, with each succeeding layer containing fewer and more specialised neurons, crowned by a single neuron responding to the complete stimulus — the 'grandmother neuron'. Ranged against them were the distributionists, who considered that each object was represented by a network of neurons, each responding to some aspect of the stimulus. Gross's face neurons were pounced on by the hierarchists but, as so often in biology, the answer lies somewhere between these extremes — although neurons exist that are tuned to objects of special importance, such as familiar faces, even these seem to be involved in networks that respond to different views of the same object. Unfortunately, Gross only hints at this story, so those unfamiliar with the field will pass it by. Perhaps the 'tales' of the subtitle should have been qualified with 'cautionary'. Gross has assembled here five entertaining and well-written articles culled from his life-long interest in the history of his field, all demonstrating in one way or another how interpretations of brain function, perhaps more than of any other aspect of biology, have been dominated by cultural, religious and philosophical influences. The articles have all previously been published, most in the journals The Neuroscientist and Trends in Neurosciences. The strength of these influences are a theme of the first chapter, which traces the development of the main theories about the function of the cortex from ancient Egypt to the seminal work of David Hubel and Torsten Wiesel on the organisation of the visual cortex, published in 1965. For example, for many centuries the Church considered the properties of thought, judgement and memory to be associated with the soul and thus too fine to be located in the gross substance of the brain tissue. Rather they were lodged in the three ventricles, a theory that also reflected thinking in law and architecture. Echoes can be heard even today, as we still discuss whether the mind and spirit are manifestations of the physical brain or somehow have their home somewhere else. Despite the Church's hegemony, literature stressing the importance of the brain tissue had existed since Galen in the 1st century AD and this view surfaced again with the rebirth of anatomy in the 16th century — in which Leonardo da Vinci played an important part (Chapter 2). However, the cortex was variously seen as glandular or, as proposed by Aristotle, for cooling the blood and not until the late 18th century was it accepted as the seat of higher mental activity. Another hundred years was required before its division into specialised regions began to be recognised but this was not fully established until well into the 20th century. In the final chapter the story of the visual cortex is brought up to 1982, by which time the roles of the parietal lobe in spatial vision and the temporal lobe in form vision had been established. A couple of paragraphs outline current thinking on the multiplicity of visual areas that have now been identified (a more detailed account can be found in Vision and Movement, eds R. Caminiti et al., HFSP, Strasbourg, 1997; www.hfsp.org). In the course of this history, ideas that we now consider to be 'correct' were often sidelined because they did not fit with contemporary thinking and sometimes were completely ignored. Sensory and motor functions for the cortex were proposed early in the 18th century by Emanuel Swedenborg, the subject of the third essay, who also described the body map in the motor cortex. But he worked outside the intellectual main stream, embedding his ideas in books on the human soul that verged on the mystic and were probably never read by others studying the brain. Not just 'publish or perish' but 'publish in the right places ...'. The cortical motor map was validated only in 1870. Another essay, on the vicious 19th century dispute between Richard Owen and T. H. Huxley over the evolution of the human brain, highlights how easy it is to interpret what one sees in the light of one's pet theory. Owen supported his view that humans could not have descended from apes with the contention that three specialisations are present only in the human brain. The chief of these was the 'hippocampus minor', an insignificant ridge on the wall of the lateral ventricle. With much hullabaloo, culminating in his famous debate with Bishop Wilberforce, Huxley demolished Owen, who had ignored the structure clearly shown in the illustrations of ape brains that he had borrowed, without permission, for his articles. The term hippocampus minor disappeared from the literature, although not before it had come in for considerable ridicule, including an appearance as 'the hippopotamus' in Charles Kingsley's The Water Babies. As a collection of essays, the book suffers from much repetition — although some cross-references have been added. The level is also uneven: the last chapter will probably be difficult reading for anyone not conversant with the intricacies of cortical anatomy. The focus is on brain and visual cortex, and I was disappointed to find little on the history of memory, another field full of pitfalls and cul-de-sacs. And it is a pity that several typographical errors were not corrected in the reprinting. Even so, Gross's essays are to be recommended as an overview of the tortuous routes to contemporary understanding of cortical organisation, with the subtext that we may still not have got it right!