From wax tablets to computers

Is a metaphor-free science possible? Could we have done without hearts as pumps, atoms as miniature solar systems, or more recently, genes as selfish? Perhaps not. Metaphors are models; they help us conceptualise objects and phenomena we do not understand in terms of things and processes we think we do. Metaphors are powerful and sometimes dangerous, they can help science advance but they also shape our thinking in ways that can be unhelpful. Selfish genes and brains as telephone exchanges may fall into this last category. There is a tendency, especially in biology, to analogise living processes to whatever is the most advanced of contemporary technologies, from ancient potters' wheels and wax tablets to present-day computers. Some years ago, Joan Safran and Pat Wall identified three different types of metaphor: poetic metaphors that hint at relationships between the known and the unknown, as in Rutherford's atomic solar systems; evocative analogies, where a principle from one sphere is transferred to another - thus prior to Newton, because everything that moved was either pushed or pulled, the movement of the sun across the sky required Apollo's chariot; and finally, metaphors of structural identity - hearts really do work like mechanical pumps.

No area of science has been more metaphor-rich than the study of mind, brain and memory. Memory was a mystic writing pad for Freud, a vast storehouse in inner space for St Augustine, a theatre or palace in which items to be remembered were located and could be recovered at will for a hermeneutic tradition that stretched from the ancient Greeks to Giordano Bruno. (Professional mnemonists use this technique, and you will find the same metaphor, and techniques of "artificial memory", employed if you respond to one of those ads in a Sunday newspaper on how to improve memory.) Douwe Draaisma, a lecturer in the history of psychology at Groningen, has written a superb history of such metaphors of memory. It is a history that gives him a framework within which to discuss changing ideas of the mind-brain relationship and its representation in western thought from ancient times to the connectionist models that became fashionable in the 1990s. Richly illustrated, the book has been felicitously translated and updated from the Dutch edition first published in 1995. Draaisma opens with a discussion on the role of metaphor in first describing and sometimes ultimately naming a phenomenon ("substituting"). Analysing the use of metaphors in psychology - hard enough to do without resorting to metaphors oneself - opens the way to its reciprocal, an account of the psychology of metaphorising, a delightful double image. There is a notable absence of any analysis of metaphors along the Safran-Wall line, or reflections on the relevance of metaphors as illustrating the ideological and/or technological roots of such theory-making, but nonetheless Draaisma's account is richly thought-provoking.

While the wax tablet-through-camera-obscura-to-computer progress of memory metaphors is at least familiar in outline, there is also much less well-known material here. It is fascinating to learn that the first attempt to quantify the possible limits of human memory was made by a Gresham College professor, Robert Hooke. Based on the number of ideas that could be acquired in a second, and the number of seconds in a lifetime, allowing for sleep and lapses of attention, he arrived at a figure of 100 million. Not so very different, as Draaisma points out, from that arrived at by present-day connectionists (one of whom calculated that the human hippocampus can store precisely 36,500 memories). There are problems with decomposing ideas into such granularity, but the calculation is fun.

Unlike many historians, Draaisma is not afraid to bring his account right up to date. He devotes considerable space to the brief history of computer analogies for mental processes, from perceptrons through to spun glass. It is possible to detect a certain mourning for the demise of the briefly fashionable holograph metaphors of the 1980s, which he sees as being resurrected via connectionism. Being a systems-oriented historian of psychology rather than neuroscience, Draaisma misses the equally briefly fashionable molecular metaphors of memory that appeared around the same time. For a decade or so the idea persisted that because DNA and RNA were christened "informational macromolecules", then brain, genetic and immunological "memory" were argued by some molecular biologists to involve, if not identical then at least very similar information-storage processes, embedded in these macromolecules.

The very meaning of memory, Draaisma points out in his epilogue, is transformed by the analogies we use to describe it. A science of memory devoid of metaphor, he suspects - and I agree - is probably impossible. If in the last analysis he prefers Freud's mystic writing pad to any other, it is perhaps because this gives humans both the flexibility and sense of wonder that any reflection on our own extraordinary memories must provide.

Steven Rose is director of the brain and behaviour research group, Open University.