[Structure of the cerebral cortex. Intrinsic organization and comparative analysis of the neocortex]

We review our present knowledge on the intrinsic organization of the neocortex based on studies carried out with the Golgi method in several mammalian species. An outline is presented on certain general aspects of the termination of specific afferent fibers in layer IV in insectivora, rodents, carnivora and primates. The principal components of the cerebral cortex have been classified in two broad types: pyramidal cells, which account for nearly 70% of the total population, and intrinsic neurons. We review different morphological characteristics of pyramidal cells and intrinsic neurons with a full description of cell varieties, dendritic morphology and several aspects of synaptic connectivity of intrinsic neurons in comparison between different species. Special attention has been paid to the description of spinous stellate cells which seems unique for a given animal species. We have reviewed intrinsic cortical circuits linking several neocortical layers, the distribution of dendritic plexuses, and the excitatory and inhibitory synaptic connections established between various neuronal categories. We finally review modern concepts of functional neocortical architecture based on the modular organization of the cerebral cortex, concluding that the cerebral cortex is rather uniform at en elementary level but the differences appear substantial when the comparison is made between different species.