Network formation through activity-dependent neurite outgrowth: a review of a simple model of homeostatic structural plasticity
Van Ooyen, A. (2017). In: Van Ooyen, A., and Butz-Ostendorf, M., eds. The Rewiring Brain: A Computational Approach to Structural Plasticity in the Adult Brain. San Diego: Academic Press, pp. 95-121.
Both during development and in adulthood, neurite outgrowth is influenced by neuronal electrical activity. High activity levels suppress outgrowth, and low levels, provided they do not fall below a minimum value, promote outgrowth. In this chapter, I review one of the first models of structural plasticity, devised to unravel the implications of activity-dependent neurite outgrowth.
In the model, each neuron has a circular neuritic field, which expands when the neuronís electrical activity is below a homeostatic set-point and retracts when it is above the set-point. Neurons connect when their neuritic fields overlap. Many interesting phenomena emerge from this simple model. The neurons self-organize into a network via a transient phase of high connectivity before reaching activity homeostasis. At equilibrium, network connectivity is critical and, owing to inhibitory cells, has a clustered structure. Although lacking intrinsic growth differences, excitatory and inhibitory cells differentiate in size. Network connectivity self-repairs following cell loss (stroke) and reorganizes after insertion of new cells (neurogenesis). In addition, the network can produce retinal mosaics and generate developmental transitions in cognition.
Together, the results show that homeostatic regulation of activity through activity-dependent neurite outgrowth is a potent driving force for both network development and network reorganization.