The Role of the Escape Swim Motor Network in the Organization of Behavioral Hierarchy and Arousal in Pleurobranchaea1

Abstract

The escape swimming pattern generator of the notaspid opisthobranch Pleurobranchaea drives a high threshold, override behavior. The pattern generator is integrated with neural networks of other behaviors so as to coordinate unitary behavioral expression and to promote general behavioral arousal. These functions are separately produced by different swim network elements. One set of swim premotor neurons, the A1/A10 ensemble, A3 and IVS, generate the swim pattern and, through corollary activity, suppress potentially conflicting feeding behavior by exerting broad inhibition at major feeding network interneurons. A second set of swim neurons, the serotonergic As1–4 neurons, provides intrinsic neuromodulatory excitation to the swim pattern generator that sustains the escape swim episode through multiple cycles. The As1–4 also provide neuromodulatory excitation to important modulatory, serotonergic cells in the feeding motor network and locomotor network, and may have a general regulatory role in the distributed serotonergic arousal network of the mollusk. The As1–4 appear to be also necessary to both avoidance and orienting turning, and are therefore likely to be critical, multi-functional components upon which much of the organization of the animal's behavior rests.