Propagation Delays in the Development of SOMs and Abnormal Brain Growth in Autism

The conventional self-organizing map (SOM) model assumes that all neurons in the neighbourhood of the neuron closest to a stimulus instantaneously react to it and adjust their weights. This paper considers the more biologically realistic scenario that acknowledges delays inherent in the propagation of signals. We show that propagation delays can significantly affect performance of SOMs -an increase in the dilution factor (a parameter in the proposed model that controls the adjustment of responses to overlapping stimuli) or a decrease in propagation speed will negatively affect coverage of stimuli. For large dilution factors the topological structure of the maps is also compromised. A parallel is suggested whereby brain overgrowth characteristic of early development stages in autistic children may lead to poorly structured cortical feature maps.