Neural Network Analysis in the Snail Brain

Abstract

How can we hope to use the techniques of cellular neurobiology, which have been successfully used to analyze the properties of single neurons or small networks, to eventually understand a structure such as the snail brain which contains about 25,000 neurons? Our approach has been to carry out detailed analyses of specific neural networks underlying several types of function in the brain of the pond snail, Lymnaea, while collecting less specific information on more global aspects of brain organization and the larger scale of interactions within it. The concentration of the CNS into a compact brain and the distribution of cells of the same type over several ganglia (see, for instance, the neurosecretory cells of Fig. 1A) makes such a whole brain analysis almost inevitable even for simple mapping studies, but the global aspect of organization within the snail brain is also emphasized by our analysis of two interneurons that have follower cells in at least five of the ganglia of the CNS (Fig. 1C,D). Even neural systems underlying specific behavioral acts can be widely distributed and motoneurons responsible for whole body withdrawal responses occur in all nine ganglia of the central ganglionic ring (Fig. 1B).