Is the cerebral cortex modular?

Abstract

Two types of modular subunit, differing in size, have been hypothesized to exist in the cerebral cortex. The first, known as a mini-column, consists of a group of 110 +/- 10 cells which form a fascicle about 30 micrograms in diameter oriented perpendicular to the cortical surface. Mini-columns are believed to be organized into larger modular groupings, referred to here as macro-columns, with a diameter of about a millimetre or less. Nicholas Swindale argues in this article that there is very little real evidence in favour of either type of module. As an alternative, he suggests that the diversity of types of columnar organization, both within and between different cortical areas, may reflect the diversity of types of information stored in the cortex. Consequently, columnar organization can be expected to vary within and between species, and even between different individuals of the same species. This new interpretation is in line with current neural network theories, which do not demand the existence of structural modularity, but show how complex forms of organization can result from the existence of simple processing rules between the elements of a structure given complex structured inputs.