BOOK REVIEW / Into the heart of the human brain: 'Bright Air, Brilliant fire: On The Matter of the Mind' - Gerald Edelman: Viking, 20 pounds

'WHAT is mind? No matter. What is matter? Never mind.' This wordplay highlights the long and acrimonious divide between biological and psychological approaches to mind. There are those who take their lead from Darwin. They see mind as a material product of biological evolution, a system of neural 'wires' or the necessary outcome of a reductionist genetic code. Others, taking their lead from Freud, have seen mind as 'psyche', a psychological entity in its own right, largely independent of brain structure.

We know from the beginning that Nobel laureate Gerald Edelman's book will bring a fresh approach to this stale dispute: his dedication is to Darwin and Freud. His declared purpose is to bring together what we know about our minds, or selves, from our psychological experience with what neuroscience now knows about the workings of the brain. Both, he argues, are formative. He wants to put mind back into nature and nature back into mind.

Like others who write on mind in the age of artificial intelligence, Edelman wants to distance himself from notions that the brain is a computer. Minds are conscious, computers aren't. Minds have experience, computers don't. But, also, consciousness in the brain is associated with evolving structures that in no way resemble the point-to-point wiring systems in computers.

For Edelman, like William James, the human brain is more a dynamic process than a thing. His theory of 'neural Darwinism' suggests the brain is constantly laying down new neural pathways in response to the environment and to its own internal experience. It is a marvellously flexible organ whose ever-changing structure first originates in response to cellular movement within the developing embryo and continues throughout life. No two brains have the same experience, no two brains are alike. No brain is like itself from moment to moment. The genetic code is more a set of constraints than a blueprint.

Edelman's own theory of consciousness is 'based remorselessly on physics and biology'. He suggests the key to basic problems of mind can be found in the brain's complexity and by fundamental new organising principles that originate at the level of complex biological systems. The brain has many, many levels of structure and organisation, each of which has evolved in different ways, at different times, in response to different needs. Each level is linked by a system of interactive loops. The whole construction 'is more like a jungle than a computer'.

Edelman restricts his project to the human mind and the human brain. He thinks he can identify those brain structures and processes associated with human consciousness. But this association does not lead to a general theory of what consciousness is, with what fundamental physical processes it might be identified, or how we might decide whether other things or creatures are conscious. He is dismissive of those who think physics important to understanding consciousness. In these senses, Edelman's book must disappoint the philosopher and the physicist. None the less, his strictly biological approach is a valuable first step.

Bright Air, Brilliant Fire is one of those rare books that comes alive in the reader's hands. It is beautifully written, conveying the clarity and passion of Edelman's creative thinking, and making neuroscience compulsive reading for the layman.