When common sense and philosophy fail...

Ian Glynn, a Cambridge physiologist and fellow of Trinity College, is learned and lucid. An authority on the mechanisms of neural conduction - the key to how the senses signal the world and control our muscles for behaviour - Glynn, in the Cambridge tradition established by Lord Adrian and Keith Lucas, pioneered new and important accounts of the physical and physiological basis of mind.

Though An Anatomy of Thought is scientifically sophisticated and in places detailed, the author has been careful to lead the non-specialist reader to ideas at the forefront of current knowledge, where science is gradually answering questions from ancient philosophy and coming up with surprises. As common sense and the insights of philosophers fail, we turn to science, and Glynn's book is a sound and balanced guide to present knowledge of brain and mind. The book does not depend on gimmicks; the issues so clearly stated in it carry their own power to attract interest and stimulate imagination.

As might be expected, and rightly so, the account is guided by and illuminates the significance of Darwinian evolution by natural selection, of which T. H. Huxley, when he grasped it, said: "How extremely stupid not to have thought of that." Huxley went on thinking about it for the rest of his life, and we in turn continue to absorb its deepening implications. Glynn does more than summarise these complex issues. He considers the problems that Charles Darwin had to face when writing On the Origin of Species , especially from knowing nothing of how inheritance works, and this tells us much about creative science and its risks and rewards. Although Darwin believed that the human brain and mind evolved from apes, Alfred Russel Wallace invoked "intelligent intervention" to account for the extra survival requirements of humans and the larger size of our brains. It is still not fully understood why our brains (compared with body weight) are so large, or just what were the evolutionary pressures that made us so inventive that technology has removed us from our biological past. Such questions keep the excitement going, with a continuous flow of fresh ideas and discoveries.

Following a detailed account of mechanisms of neural conduction, we are taken on a "Cook's tour" of the anatomy of the brain: to seeing and illusions; to abnormal vision (including bizarre phenomena of agnosias where meaning is lost); to the recent technological wonders of imaging brain functions and "opening the black box" with direct recording of electrical activity in the brain. This reviewer would have liked more on brain imaging and the problems of interpreting or "reading" functions from which regions are active in various conditions - when thinking, seeing, imagining and so on - but one cannot have everything. A short section on artificial neural nets leads to more extended discussions of speech, memory and generally "thinking about thinking". Then comes consciousness.

Here ideas of the American philosophers John Searle and and Daniel Dennett are discussed briefly with emphasis on the status of sensations, or "qualia". There are few if any answers. But puzzling issues are put clearly, especially Dennett's virtual rejection of qualia as a modern behaviourism. Central is the question of what, if anything, consciousness does: if it does nothing, why should it have evolved? And how can we say anything meaningful about sensations? Yet, it can be said that seeking pleasant and avoiding unpleasant sensations is a primary goal of behaviour,and is what most of us seek most of the time. Discussing Dennett's virtual rejection of qualia of consciousness as too bizarre and lacking in effects to be accepted at their face value (although sensations seem to be our most certain and most intimate window on the world), Glynn questions whether consciousness is indeed ineffective. The remarkable phenomenon of "blind sight" and sleep walking give but very limited behaviour, lacking initiative and creative intelligence. So perhaps consciousness is causally important, as well as giving significance to our personal lives. However this may be, Glynn sets the scene and directs our attention to these imponderables without stepping dangerously beyond the caution of science.

Richard Gregory is emeritus professor of neuropsychology, University of Bristol.