THE PRIVATE LIFE OF THE BRAIN. By Susan Greenfield. Allen Lane pound;18.99

The mind is its own place, and in itself Can make a heaven of hell, a hell of heaven.

Thus said Milton's Satan (Paradise Lost, Book I, line 249) and thus argues Professor Susan Greenfield, give or take a neuron or a million and a "busy crowd" of neuro-chemical transmitters.

In her engaging but ultimately frustrating account of the way consciousness is generated, Professor Greenfield tells us a lot about the physical configuration of the brain, how she envisages the mind (basically, the brain in action) and a bit about what she calls the self (how the brain in action thinks of itself). To these fascinating subjects she brings her expertise as professor of pharmacology at the University of Oxford.

In concise footnotes, she lays out what is known so far about the electrical (neuronal) networks, chemical exchanges and hormonal surges that flit through our grey matter. A lay reader can only be dazzled.

Yet these are footnotes and necessarily cramped. A rendering for general interest can be found in John McCrone's Going Inside, published last year by Faber, which explains more fully current thinking - that mental activity resides in linkages of neurons across the whole brain rather than solely in areas dedicated to seeing, memory and so on - though there seem to be command centres for various faculties, too. And that the brain is a complex system operating and adjusting on constant feedback.

Greenfield's theory is paradoxical. Emotion, she suggests, is always present - a kind of soup in which consciousness wallows - but it is also the antidote to cognitive thought. As the antidote, it is adaptive (selected through evolution) she says, because it prevents us from withdrawing too far into the absorbing world of inner thought - by precipitating us into the here and now, emotion keeps us physically aware enough to survive. Here Greenfield is on dodgier ground - ground well trodden by philosophers, poets, novelists and all the rest of us, who, after all, have emotions too.

Are all emotions solely of the kind experienced at a rave or in orgasm in which as she argues, we abandon thought? I suggest not. Just think of the triumph felt on solving some cognitive problem. And is emotion always used to flee the compulsion to withdraw into thought? Don't many people (academics, for instance) use the pursuit of thought to avoid the pressure of emotion?

Furthermore, and most importantly, most emotions are not akin to the thrill of bungee-jumping (Greenfield's prime example). Most of our emotions are directed at others. When not aroused by specific relationships, emotions are still governed by value systems which many psychologists explain as rooted in early emotional attachments. Such social and familial aspects to emotion - and to the organisation of our attitudes through it - are absent here.

Philosophers would call her approach solipsistic. And, like Milton's Satan, she is also a mentalist, despite her focus on the mechanics of the brain and identification of that physicality with the more tenuous concepts of mind and self. Like University of Iowa neuroscientist Antonio Damasio, Greenfield acknowledges that the brain is intimately linked (via the neuro-chemicals of emotion) to its host body. Yet without cultural contexts, that linkage is content-free, null, empty.

Greenfield is dismissive of Daniel Dennett, philosopher and author of Consciousness Explained (Penguin, 1993), who points to language as the primary route not just for communicating, but also for understanding. But if experience orders the brain's electro-chemical functioning, as Greenfield shows, with so much of our experience being language-mediated, surely language (a cultural construct) must also play a part?

To return to Paradise Lost, Satan's words strike a chord. We all know preconceptions can colour our experience. Yet Milton puts these words into the mouth of the Satan. And, in the next few books of Paradise Lost, Satan is banished to Hell and discovers, along with the reader, that it is nothing like Heaven, whatever he claims.

No brain leads a life so private that the world cannot impinge. And if it did, it would not be, in any recognisable sense, human. Consciousness remains to be explained.

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