BOOK REVEIW / What's the matter with mind?: 'Bright Air, Brilliant Fire' - Gerald Edelman: Allen Lane, 20 pounds

We wear our thinking caps on the inside. The part that sets us apart, the cerebral cortex, is a quarter-inch-thick rind covering three pounds of brain. We incline, however, to a more elegant image of ourselves: consciousness is founded in a unifying

sense of self. Each of us has a single point of view, and we like to imagine the self as having a nucleus or focus. Descartes identified the pineal gland as the interface between mind and brain. Nowadays, a typical lay thinker might conjure up a mental cartoon of a control room full of screens. Of course, this demands a controller.

Gerald Edelman is hardly the first neuroscientist to point out the absurdity of the 'homunculus' model: nothing is explained by postulating that a little man sits inside the head interpreting information from the outside world, since another homunculus is required to interpret his interpretations, and so on ad infinitum. Nor is he the first thinker to ridicule those who feel the need to mystify consciousness - in 1949, Gilbert Ryle used the inspired image of the 'ghost in the machine' to illustrate the Cartesian error of separating matter and mind.

But such is the power of the sense of self, and the sense that consciousness is an ineffable mystery, that challenges to the materialist orthodoxy of neuroscience are almost guaranteed a good press. One example is Roger Penrose's The Emperor's New Mind, which suggested that the explanation of consciousness may lie in quantum physics.

Edelman mounts a heavy-calibre counterblast on behalf of the belief that mind is solely a product of matter, acting according to 'normal' physical laws. Furthermore, he predicts, the mind will become increasingly amenable to scientific description. Building on ideas expounded in three previous books, the Nobel laureate argues that the brain can only be understood if treated as a product of evolution. Rather than genes, however, he emphasises selective pressures that act on groups of neurons as

each individual nervous system develops - 'neural Darwinism'. With a million billion connections in the cortex, the scope for uniqueness is beyond imagination.

Information from the outside world (and from other parts of the organism) is represented as maps made up of arrays of neurons. The cortex might be seen as a sort of atlas in which the maps compare notes, and thereby generate a collective awareness. One drawback of the map metaphor, however, is that it encourages a false sense of simplicity - as does any metaphor involving human constructs, including mental ones. The brain, Edelman warns, is more like a jungle than a computer.

This applies to so-called 'neural net' computing, which is not greatly like real neural networks. It also implies that modern cognitive science, despite its ascendancy, is a castle in the clouds. Abstraction is deviation, Edelman maintains; psychology must be rooted in biology. In fact, he looks forward to a scientific globe dominated by two superpowers, physics and neuroscience, the latter incorporating psychology. The book is dedicated not only to Darwin but also to Freud, the 'biologist of the

mind'.

A notable target of Edelman's assault on cognitivism is the idea that the human brain incorporates a dedicated device for acquiring language, which inducts children into a community of speech. Edelman argues, contrary to Noam Chomsky, that language does not enjoy a status separate from the rest of cognition: a child can make sense of things before it can speak.

At times, making sense of this particular text requires a daunting degree of cortical organisation. To a scientist, the kind of writing entailed in a book for a lay readership probably seems like free verse, but there nearly always remains a gulf of

language to be bridged. Some scientists adopt an unconvincing folksiness; Edelman is more like a scoutmaster leading his callow charges on an Outward Bound course, commiserating briskly about its rigours.

His prose is cogent, profound and authoritative, but somewhat short on legitimate ways to ease comprehension, such as illustrative examples. Still, Edelman does note the importance of metaphor in mental activity, as the imagination projects a map from one domain onto a map from another, and gains insight through the comparison. The more the maps are of familiar territory, the happier a general readership becomes.