Network stability from activity-dependent regulation of neuronal conductances

Activity-dependent plasticity appears to play an important role in the modi fication of neurons and neural circuits that occurs during development and learning. Plasticity is also essential for the maintenance of stable patter ns of activity in the face of variable environmental and internal condition s. Previous theoretical and experimental results suggest that neurons stabi lize their activity by altering the number or characteristics of ion channe ls to regulate their intrinsic electrical properties. We present both exper imental and modeling evidence to show that activity-dependent regulation of conductances, operating at the level of individual neurons, can also stabi lize network activity. These results indicate that the stomatogastric gangl ion of the crab can generate a characteristic rhythmic pattern of activity in two fundamentally different modes of operation. In one mode, the rhythm is strictly conditional on the presence of neuromodulatory afferents from a djacent ganglia. In the other, it is independent of neuromodulatory input b ut relies on newly developed intrinsic properties of the component neurons.