Competition in the development of nerve connections: a review of models

The establishment and refinement of neural circuits involve both the format ion of new connections and the elimination of already existing connections. Elimination of connections occurs, for example, in the development of mono neural innervation of muscle fibres and in the formation of ocular dominanc e columns in the visual cortex. The process that leads to the elimination o f connections is often referred to as axonal or synaptic competition. Altho ugh the notion of competition is commonly used, the process is not well und erstood-with respect to, for example, the type of competition, what axons a nd synapses are competing for, and the role of electrical activity. This ar ticle reviews the types of competition that have been distinguished and the models of competition that have been proposed. Models of both the neuromus cular system and the visual system are described. For each of these models. the assumptions on which it is based, its mathematical structure, and the extent to which it is supported by the experimental data are evaluated. Spe cial attention is given to the different modelling approaches and the role of electrical activity in competition.