Encephalization in mammals in relation to the size of the cerebral cortex.

A new index of encephalization has been proposed based on a reanalysis of the brain-body weight relationship in mammals. The new index, c, is related to the volume of the whole brain as well as to the surface and volume of the cerebral cortex. From an evolutionary point of view the index-cortex relationship is particularly interesting, since the structure of the brain which contributes most to its evolutionary progression is the cerebral cortex. A theory of corticalization has been developed in which the surface of the cerebral cortex is analyzed into two components, Sb, determined by the size of the animal, and Se, associated with an increase in the information-processing capacity. An analogue division has been performed for the cortical volume. Furthermore, an inquiry has been made into the brain structure which can serve as an estimator of body weight. The medulla oblongata appears to be such a structure.