Network connectivity changes through activity-dependent neurite outgrowth

There is experimental evidence that neuronal electrical activity directly influences neurite outgrowth during the development of the nervous system. Using model studies, Van Ooyen and Van Pelt extensively investigated the effect of this phenomenon upon network development and architecture. Their studies are based on the experimental observations that there is an optimal range of electrical activity at which neurite outgrowth takes place. In their model, neurite growth occurs if the activity level of the neuron is below a certain threshold, otherwise the neurite retracts. We extend their results to include a more complete description of the relationship between electrical activity and neurite outgrowth. This takes into account the experimental observation that outgrowth ceases not only when neuronal activity is too high, but also when it is below a certain threshold. The modified model displays a wider range of behaviours during network development. In some cases, for example, growth is only transient and is followed by a total loss of connections in the network. As a consequence of the larger spectrum of possible behaviours, the mechanisms for control of network formation, by the network's internal dynamics as well as by external inputs, are also increased.