Basic connectivity of the cerebral cortex and some considerations on the corpus callosum.

Studies on the connectivity of the cerebral cortex have lent strong support to the idea that the cortex is an associative network in which information is stored by ways of Hebbian cell assemblies. One of the main arguments for this is the elaborated system of cortico-cortical long-range connections which allows distant regions of the cortex to interact. Part of this system is the corpus callosum, which is responsible for the co-operation of the two cortical hemispheres. The following points are interesting with regard to interhemispheric co-operation: (1) the callosal system includes fewer neurons than the system of intrahemispheric long-range connections; (2) the mirror image activity induced by the callosal system may be advantageous for the ignition of cell assemblies; (3) the fibres of the corpus callosum differ considerably in thickness, which may be considered as anatomical evidence for more direct co-operation of the two hemispheres in some tasks rather than in others; and (4) a complex relationship between brain size and fibre thickness becomes evident in the corpus callosum, in which only some fibres seem to compensate for the longer conduction times in larger brains.