10. Formal inversion in C. elegans - A.

We have now arrived at the famous Minimal Bilateria Model of animal life called C. elegans (in the upper diagram). This tiny (1 mm long) creature is the most completely understood multicellular animal in science. It was the first to have its genome sequenced and thus provided central lessons for the human genome project.

It also has the only nervous system in a multicellular animal for which we have an essentially complete wiring diagram, including that of a Minimal Model Brain, represented by the contents of the box in the diagram. Here the black dots represent neuron cell bodies and the nerve ring is the probable homologue of the nerve ring of the hydra. This magnificent neuroscientific resource (the wiring diagram) was provided in 1986, after seventeen years of intricate electron microscopy and painstaking reconstruction, by the Cambridge team of John White, Eileen Southgate, Nichol Thomson and Sydney Brenner *. [The upper diagram and several diagrams in following posts were developed from data published in their now classic report].

The brain of C. elegans is capable of such fundamental activities as taste, smell, touch sensation and heat sensation, all of which are also central to our own lives. The mind (or working brain) of 'the worm', as it is known to its devotees, is also capable of learning, memory and thus primitive knowledge. Crucially for science however, the worm brain/mind achieves all these functions with about 180 neurons and about 4000 interconnections -- an entirely tractable conceptual challenge compared with the enormous complexity of human brains. We are thus able to begin to learn about the basic workings of brains while it is still possible to study them neuron by neuron and connection by connection.

In the next post we shall begin to look 'inside the box' at the brain of the worm.

* White J. G., Southgate E., Thomson J. N., Brenner S. (1986). The structure of the nervous system of the nematode Caenorhabditis elegans. Phil. Trans. R. Soc. London. B314, 1-340. [Also accessible on the Web at www.wormbase.org Click on The Mind of a Worm (White et al. 1986).