To Eat or Not To Eat

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Science  25 Jun 2004:
Vol. 304, Issue 5679, pp. 1877-1879
DOI: 10.1126/science.304.5679.1877e

Repetitive behaviors can be encoded within networks of neurons; one such example is the central pattern generator (CPG) that subserves feeding in the mollusc Aplysia. The neuron B8 activates closing of the radula, a hard valve-like structure that is used to grasp food. When the mouth comes into contact with seaweed, the cerebral-buccal interneuron (CBI) triggers closure of the radula as it retracts, which serves to bring food into the buccal cavity (ingestion). On the other hand, stimulation of the esophageal nerve closes the radula during protraction, which serves to expel material (egestion) that has been deemed inedible.

Proekt et al. show that the feeding program is influenced by history. Thus, identical firing episodes in the CBI can have different effects, depending on the internal state of the network. If it is in egestive mode, this behavior persists until multiple volleys from the CBI shift the pattern of B8 firing into the retraction phase. This inertial response can be thought of as an intention or expectation that the next thing to do should probably be pretty similar to the previous thing until overwhelming evidence indicates it's time to switch. — GJC

Proc. Natl. Acad. Sci. U.S.A. 101, 9447 (2004).

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