Susan Greenfield is both a scientist at the forefront of brain research and a lecturer with wide experience of making difficult ideas accessible to the general public, including children. (In 1994 she gave the Royal Institution Christmas Lectures, the first woman to do so in the series' 165 years.) With these skills she has written an excellent account of her own theory of how the brain may give rise to conscious experience. Profound ideas about how the brain works are expressed vividly and comprehensibly even for readers without a scientific background. But she does not over-simplify; she gives her readers plenty of facts, with analogy and metaphor making the subject lively even at its most technical.
At the outset, Greenfield makes an important distinction between two possible kinds of theory: those which identify what particular elements or events in the brain make up the mind, and those which account for how the mind actually emerges from them. It is the first kind she is concerned with here; the second kind is currently beyond our reach, and probably always will be. She implies that this may be just as well: "If we could explain exactly how consciousness is generated by groups of neurons under certain conditions, it would also mean that we had the ability to manipulate one another's consciousness to such a degree that it would lead to the effective annihilation of the individual."
The starting point for Greenfield's theory is gestalt theory, first put forward by German psychologists as long ago as 1912. "The idea behind the gestalt school of thought is that perception is global, not local; objects or features are perceived in relation to one another, giving a final holistic view that cannot be inferred from the individual components alone." Gestalt theory can be applied to thinking as well as to visual perception, in which case it offers an alternative to behaviourism as advocated by BF Skinner. But it still remains a psychological theory. Greenfield gives it a solid 'nuts and bolts' basis in brain function, aiming to get beyond metaphor and establish a physical basis for gestalt.
This she does with considerable persuasiveness. She provides detailed arguments in support of the view that the cortex of the brain contains groups of neurons that come together in dynamic cooperatives. These are not fixed structures but rather temporary associations that last for varying lengths of time. In a felicitous phrase she compares them to "clouds in the brain", coming or going as thoughts and associations move through the mind. Consciousness at the physiological level is thus "spatially multiple yet effectively single at any one time". Experimental evidence exists which suggests that these fluctuating associations of neurons really do exist.
Much of the book is taken up with detailed discussion of how these neuronal gestalt may be thought to function, in relation both to deeper macroscopic brain structures such as the thalamus and brain stem and also to the biochemistry of individual neurons. Here the play of activity in the cortex is related to arousal and ascending pathways, which have at least five distinct amine chemicals associated with them. In another happy phrase, Greenfield talks of "fountains in the brain".
In the final chapters she moves back from physiology to psychology and considers some of the implications of her ideas for the abnormal as well as the normal mind. What would happen, she asks, if someone's brain were unable to make neuronal gestalts larger than a certain size? Might they experience abrupt changes in consciousness as incoming impulses from the sensory world flooded the brain? If so, might this be the basis of schizophrenia? If the neuronal gestalts wee unduly large, on the other hand, certain ideas might become abnormally dominant and inhibit both other kinds of thinking and also action; this could happen in depression. Finally, there could be an almost complete absence of gestalts; perhaps this is what happens in the late stages of Alzheimer's disease.
It is not only pathological states that the theory can illuminate. Newborn babies, for example, presumably have few gestalts, and their number, size, and complexity must rise as children grow older. In adults, too, "we can easily imagine that our momentary states of awareness lie between large and small gestalt profiles as we live out each day…".
Tantalizing speculations run through the reader's mind at this point. How could the theory account for altered states of consciousness--the hypnotic state (just one gestalt, perhaps?), mystical illumination, near-death experiences? And then there is the state of 'enlightenment'. Greenfield makes one or two references to Buddhist theories of 'no self'. Buddhists claim that this is not just a philosophical idea but a direct perception, which can be obtained by suitable meditation practice and in other ways. Is it possible to account for such a perception in terms of the theory, and what kind of gestalt patterns would exist in the brain of someone who has this experience? It is a mark of the book's quality that it can start the mind running along these lines.
A truly scientific theory, says Karl Popper, should make testable predictions. Does neuronal gestalt theory do so? In principle, yes, but in practice many of the tests that could be envisaged lie just beyond the range of currently available research tools such as positron emission tomography (PET), nuclear magnetic resonance imaging (NMRI), or magneto-encephalography (MEG). The sensitivity of these methods is however increasing all the time and before long it may be possible to confirm or refute the existence of gestalts directly.
This is a rich and stimulating book. It should be read by anyone who is interested in the mind, brain, and consciousness.