Dynamic Regulators of Neuronal Form and Connectivity in the Adult Snail Helisoma

Among the most striking features to emerge from 15 years of investigation of Helisoma are the tremendous adaptability and resiliency of its nervous system and the precision with which remodeling can occur. Somewhat ironically, Helisoma was ini-tally selected for investigation because of the existence of definable behavior, especially fixed action patterns, and a nervous system that was approachable because of its relative simplicity and assumed stability. However, as the analytical precision of investigations on this system improved, the view of a nervous system of immutable circuits has been refined to encompass a much more dynamic set of capabilities. It is apparent now that these more plastic attributes may be a general property of nervous systems. One might also speculate that the responses of perturbation-induced neural plasticity are actually an amplification of ongoing events normally present in all neuronal systems.