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Neurobiology

The analytical bend of the leech

Nature volume 391, pages 18–19 (1998)Cite this article

Descartes introduced the coordinate system that forms the basis of analytical geometry in an appendix to a philosophical discourse1 that has been criticized for its contemptuous tone2. Descartes might have been more humble had he known that his great discovery had already been implemented in the nervous systems of invertebrates, and that it is used by the leech to direct a reflexive motor behaviour. The evidence provided by Lewis and Kristan on page 76 of this issue3 arrives too late for Descartes, but in time to show the rest of us how a network of neurons computes a sensory-motor transformation.

As every student of introductory physics will testify, it is one thing to set up a cartesian coordinate system and quite another to use it computationally. Lewis and Kristan provide convincing evidence that the leech bending network takes full advantage of the cartesian representation it has established. They show that the touch location inferred by interpreting P-neuron fire rates as cartesian coordinates accurately matches the actual stimulus location (3 per cent r.m.s. error). When they injected current into a P cell to modify its activity, the change in the bending response matched the shift in the coordinate value represented by the P cell's activity. Finally, they modelled how the sensory-motor transformation4,5 that directs the bend is computed.

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Figure 1: Computation of a sensory-motor transformation by neurons in the leech.
Figure 2: A simple circuit showing two P cells driving an interneuron.

References

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  1. the Volen Center and Department of Biology, Brandeis University, Waltham, 02254, Massachusetts, USA

    L. F. Abbott

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  1. L. F. Abbott
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Abbott, L. The analytical bend of the leech. Nature 391, 18–19 (1998). https://doi.org/10.1038/34032

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