DYNAMIC CONSTRUCTION OF A NEURAL-NETWORK FROM MULTIPLE PATTERN GENERATORS IN THE LOBSTER STOMATOGASTRIC NERVOUS-SYSTEM

In the stomatogastric nervous system (STNS) of the lobster Homaros gam marus, the rhythmic discharge of a pair of identified modulatory neuro ns (PS cells) is able to construct de novo a functional network from n eurons otherwise belonging to other functional networks. The PS intern eurons are electrically coupled and possess endogenous oscillatory pro perties that can be activated synaptically by stimulation of an identi fied sensory pathway. PS neurons themselves project synaptically onto the three major neural networks (esophageal, gastric mill, and pyloric ) of the STNS. When a PS is rhythmically active in vitro, either spont aneously (rarely) or in response to direct stimulation, it dramaticall y restructures the otherwise independent activity patterns of all thre e target networks. This functional reconfiguration elicited by a singl e cell does not rely on changes in neuronal allegiance to preexisting circuits, or on a simple merger of these different circuits. Rather, P S is responsible for the creation of an entirely new motor rhythm in t hat, via its widespread synaptic connections, the interneuron is able to subjugate the ongoing activity of the three STNS circuits and selec tively appropriate individual elements to its own intrinsic rhythm. In addition, PS excites motor neurons that innervate dilator muscles of a valve situated between the esophagus and the stomach. The reorganiza tion of the regional foregut motor rhythms by the interneuron is there fore coordinated to the opening of this valve, which itself carries se nsory receptors that have been found to activate bursting in PS. Our d ata suggest that the role of PS in massively restructuring stomatogast ric output is to generate a unique motor pattern appropriate for swall owing-like behavior. In a wider context, moreover, the results demonst rate that a neural network may not exist as a predefined entity within the CNS, but may be dynamically assembled according to changing behav ioral circumstances.