The Cortex as a Sensory Analyser

Abstract

The vertebrate brain has acquired seriatim in its phylogeny a sequence of brains, central structures employing afferent information for control of behavior. Each of these central brains has developed out of one or another afferent level; a medullary level related to cranial and spinal nerves; the cerebellum from Vth and VIIIth nerve nuclei; the vestibular apparatus from another division of the VIIIth, the thalamus from the IInd; and cortex from the olfactory apparatus. Each center secondarily acquires connections not only from its own level, but from all levels of the body. For instance the eye is a diencephalicstructure, but the “optic” thalamus also receives auditory and somaesthetic paths. From the primitive pallium, starting as a facilitator of olfactory function (Herrick, 1948) and still so operating as the pyriform lobe of mammals, a general cortex developed which made secondary connections with other levels; not directly, but only through the sensory centers of the thalamus. This relation is exemplified in the reptilian brain. Not until the mammal, however, were added the more direct and specific relays of the main sensory systems of audition, vision and body sense, through thalamic relay to projection cortex.

Washington University School of Medicine, St. Louis, Missouri

This work was conducted in part under contract between Washington University and the Office of Naval Research, and in part under a grant from the Supreme Council, Thirtythird Degree Scottish Rite, Northern Jurisdiction, USA, through the National Association for Mental Health