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A simple rule for axon outgrowth and synaptic competition generates realistic connection lengths and filling fractions

Lookup NU author(s): Professor Marcus Kaiser


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Neural connectivity at the cellular and mesoscopic level appears very specific and is presumed to arise from highly specific developmental mechanisms. However, there are general shared features of connectivity in systems as different as the networks formed by individual neurons in Caenorhabditis elegans or in rat visual cortex and the mesoscopic circuitry of cortical areas in the mouse, macaque, and human brain. In all these systems, connection length distributions have very similar shapes, with an initial large peak and a long flat tail representing the admixture of long-distance connections to mostly short-distance connections. Furthermore, not all potentially possible synapses are formed, and only a fraction of axons (called filling fraction) establish synapses with spatially neighboring neurons. We explored what aspects of these connectivity patterns can be explained simply by random axonal outgrowth. We found that random axonal growth away from the soma can already reproduce the known distance distribution of connections. We also observed that experimentally observed filling fractions can be generated by competition for available space at the target neurons -a model markedly different from previous explanations. These findings may serve as a baseline model for the development of connectivity that can be further refined by more specific mechanisms.

Publication metadata

Author(s): Kaiser M, Hilgetag C, van Ooyen A

Publication type: Article

Publication status: Published

Journal: Cerebral Cortex

Year: 2009

Volume: 19

Issue: 12

Pages: 3001-3010

ISSN (print): 1047-3211

ISSN (electronic): 1460-2199

Publisher: Oxford University Press


DOI: 10.1093/cercor/bhp071

PubMed id: 19435708


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Funder referenceFunder name
EP/G03950X/1Engineering and Physical Sciences Research Council
EP/E002331/1Engineering and Physical Sciences Research Council
RG/2006/2Royal Society