Neuronal correlates of corticalization in mammals: a theory.

The cerebral cortex of mammals has been found to be uniformly organized, and to be composed of elementary processing units or modules having an essentially constant number of neurons. In the present paper the hypothesis is put forward that the relative proportion of local circuit neurons (LCNs) within a module reflects the evolutionary level of corticalization of a mammal. The modules, in turn, are interconnected so as to form basic neuronal networks or columns with a species-specific width varying from 90 to 310 microns. A mathematical formalism is presented from which the hypothetical ratio between LCNs and projection neurons, as well as the size of the cortical column and the number of modular units that it contains, can be calculated.