Colonne corticale

A cortical column is a group of neurons forming a cylindrical structure through the cerebral cortex of the brain perpendicular to the cortical surface. The structure was first identified by Mountcastle in 1957. He later identified minicolumns as the basic units of the neocortex which were arranged into columns. Each contains the same types of neurons, connectivity, and firing properties. Columns are also called hypercolumn, macrocolumn, functional column or sometimes cortical module. Neurons within a minicolumn (microcolumn) encode similar features, whereas a hypercolumn "denotes a unit containing a full set of values for any given set of receptive field parameters". A cortical module is defined as either synonymous with a hypercolumn (Mountcastle) or as a tissue block of multiple overlapping hypercolumns. Cortical columns are proposed to be the canonical microcircuits for predictive coding, in which the process of cognition is implemented through a hierarchy of identical microcircuits. The evolutionary benefit to this duplication allowed human neocortex to increase in size by almost 3-fold over just the last 3 million years. The columnar hypothesis states that the cortex is composed of discrete, modular columns of neurons, characterized by a consistent connectivity profile. The columnar organization hypothesis is currently the most widely adopted to explain the cortical processing of information. Cerebral cortex The mammalian cerebral cortex, the grey matter encapsulating the white matter, is composed of layers. The human cortex is between 2 and 3 mm thick. The number of layers is the same in most mammals, but varies throughout the cortex. In the neocortex 6 layers can be recognized although many regions lack one or more layers, fewer layers are present in the archipallium and the paleopallium. The columnar functional organization, as originally framed by Vernon Mountcastle, suggests that neurons that are horizontally more than 0.5 mm (500 μm) from each other do not have overlapping sensory receptive fields, and other experiments give similar results: 200–800 μm.