The first part of The Cerebral Code is a hypothesis about the functioning of the human brain. In neocortical layers of superficial pyramidal neurons, lateral excitation is strongest not between adjacent neurons but at a distance of about 0.5mm. Mutual re-excitation will therefore produce triangular activation patterns and systems of hexagonal repeats. The competitive replication of these hexagonal patterns provides the basis for a "Darwin Machine". (This is a poor summary of a complex explanation replete with neurobiological detail and visual and musical analogies.)

The second part looks at the role such a Darwin Machine could play in cognitive functions like short term memory, working space limits, associative memory and convergence zones, long-distance communication and synchronisation, metaphors, and creativity. (This is largely independent of the particular implementation of such a Machine, and hence of the preceding neurobiological hypothesis.) Using the abstraction provided by the concept of a Darwin Machine, Calvin draws analogies with aspects of genetic evolution and population biology such as biogeography, sex, founder effects, and niches. As well as all this he offers an account of the historical and personal background to his ideas.

I was initially solidly sceptical about the central idea of The Cerebral Code, but my wariness diminished as it became clear that Calvin wasn't suggesting it as an explanation for everything (a trap into which many with novel ideas about brains and minds fall). His final chapter looks at how his ideas might connect with other approaches to the brain, approaches at different levels of explanation or addressing different aspects of brain function. Calvin's recognition that he doesn't have all the answers is refreshing. If his ideas are provocative, they are also testable (he suggests some experiments himself); and even if you aren't convinced, The Cerebral Code is still an enjoyable way to learn something about neurobiology and abstract Darwinian processes.

Calvin has done his best to make The Cerebral Code popularly accessible, but it covers a lot of ground and will probably be appreciated most by those with a background in the biological sciences. Some introductory information is provided in a glossary, but the terms that appear in that are not marked on first appearance in the text, reducing its usefulness. This seems to be symptomatic of a more general problem, since the endnotes contain the page numbers of their anchors, but these are completely unmarked in the text itself! Perhaps there was a hypertext to print translation failure somewhere in the publishing process.

February 1997

External links:

- buy from Amazon.com or Amazon.co.uk
- details at the MIT Press
- information from William H. Calvin

Related reviews:

- more human biology
- books about neuroscience
- more popular science
- books published by The MIT Press