Figure 1.

The Hydra nerve net and its proposed functions. (a) The Hydra nerve net is visualized by labelling neurons with GFP and imaging with a spinning disc confocal microscope. (b) The Hydra nerve net is composed of three major proposed behaviour-generating networks: the contraction burst network correlated with longitudinal contraction, the rhythmic potential 1 (RP1) network correlated with elongation, and the rhythmic potential 2 (RP2) network correlated with radial contraction. In addition to these proposed behaviour-generating networks, the RP1 network is also active during Hydra ‘rest’ when the animal is kept under constant external conditions and exhibits no observable behaviour [1,34].