Neuronal Synchronization and Bidirectional Activity Spread Explain Efficient Swimming in a Whole-Body Model of Hydrozoan Jellyfish.

Aquatic animals need tightly choreographed movements to efficiently navigate through open waters. Radially symmetric animals, like jellyfish, face the additional challenge of having to respond to regionalized sensory stimuli at the margin of their bell with an orchestrated motor response that initiates predation or escape. The nerve net of hydrozoan jellyfish comprises a condensed ring of electrically coupled neurons, that process sensory input and control the motor output. Here, we aim to understand the coupling of neural activity and motor response by developing a biophysical computational model of the swimming-motor-net of a hydrozoan jellyfish and let it control a swimming jellyfish in a fluid simulation. We find that the neuron activity can synchronize while the signal travels around the ring, eventually triggering a bidirectional wave of activation in the muscles. This mechanism explains seemingly contradicting electrophysiological experiments and minimizes muscle contraction time. Hydrodynamical simulations demonstrate that this setup enables symmetric movement even if neural input is highly asymmetric. We hypothesize that the development of this ring structure supports the jet propulsion by which hydrozoan jellyfish swim. These findings show the importance of considering whole body anatomy and movement when investigating neural design.