Current thinking and linking

What is a neuroscientist doing writing a book on consciousness? The question comes from the author himself, anxious lest he appear to trespass on philosophers' exclusive ground. But he has no need to be defensive. In the free-for-all that is consciousness studies today it is refreshing to have the speculations of philosophers and others assessed in the light of empirical data from those scientists who study the brain itself.

The most interesting parts of the book are those describing experimental techniques, such as Pet (positron emission tomography) scans and MRI (magnetic resonance imaging), which allow researchers to monitor those parts of the brain that are active during different mental tasks and experiences in conscious subjects. The clear accounts of these brain-imaging tools convey the exciting possibilities they offer as well as the difficulties of planning and interpreting experiments.

For example, you can measure the activity of a certain brain area when the subject is looking at an object, and compare it with the activity when the subject is just thinking about the object. But researchers are deeply divided over how to determine the "baseline" condition, where the subject is neither looking nor thinking. You can tell when someone is physically still, but how can you be sure whether he or she is mentally still? A person may be day-dreaming, or the mind could be active in the very effort to keep blank, and such things could make a nonsense of your careful observations.

Max Bennett's own research area concerns the connecting-points (synapses) between different brain or nerve cells. The distressing symptoms associated with a wide variety of medical conditions, from strokes to schizophrenia, relate to a failure of these connections to work properly. The relevance of neuroscience to consciousness at this point is crystal clear, as is the possibility of dramatic relief. Bennett's commitment to the clinical application of neuroscience shines through, as when he describes work on rats with senile dementia. After treatment with embryonic brain material their memories are shown to be restored to the efficiency they had in their prime.

The tabloid press may trumpet such treatment misleadingly as "brain transplants" and the moral questions aroused by the need for foetal material are real enough. But the link between the physical condition of the synapse and the mental condition of the subject - and the opportunity this offers for therapy - is beyond doubt.

Experimental work of this kind raises the question of how far consciousness stretches down the animal kingdom. Bennett has a chapter on the evolution of consciousness in which he compares the brains of different species and the approaches to determining whether, or which, non-human animals are conscious. In an attempt to locate the site of visual consciousness in the primate brain, he gets drawn into a discussion of work on "blindsight" (non-conscious visual awareness) in humans and monkeys. Though interesting in itself, its relevance to his main theme is questionable.

Also unsatisfactory is the final chapter on consciousness and quantum mechanics. As a survey of its subject it is too brief to be adequate and unlike other parts of the book it does not draw usefully on the author's own field of neuroscience to illuminate debate.

Overall the book is an engaging personal view of a wide subject from the standpoint of one discipline involved in it.

Revd Anthony Freeman is managing editor, Journal of Consciousness Studies.