Neuronal interconnection as a function of brain size.

The effect of increasing brain size upon the degree of interconnection between neurons is analyzed. An explicit model suggests that as the brain is scaled up there must be a corresponding fall in percent connectedness (the fraction of cells with which any one cell communicates directly). The reason for this is that if the percent connectedness is to be maintained in the face of increased neuron number, than a large fraction of any brain size increase would be spent maintaining such interconnection while the increasing axon lengths would reduce neural computational speed. One implication is that larger brains, being necessarily limited in allowable interconnectedness, may tend to show more specialization.