The Limbic System

Abstract

A limbus is a rim or margin. In 1878, Broca suggested the term “limbic lobe” for those anatomical structures that encircle the third ventricle and the sagittally sectioned corpus callosum. This portion of the brain was thought to be functionally restricted to the perception of the sense of smell. In 1937, Papez reviewed clinical evidence suggesting that these médial structures and their connections were involved in emotion. MacLean (1949, 1952) proposed that these anatomical regions might together form a functional unit; he introduced the term “limbic system.” The last two decades have seen a better definition of the anatomical interrelationships of structures within this system and an expansion of its borders to include parts of midbrain, thalamus, and neocortex. Some neuroanatomical authorities still resist the concept of a limbic system; for example, Brodal (1969) includes definite olfactory structures within the rhinencephalon and distributes other portions to the traditional cortico-thalamic-reticular system, doubting the existence of a limbic system as a functional entity. Livingston and Escobar (1971) argue that the anatomical expansion of this system beyond medial brain structures confuses the original limbic concept of Broca; they propose using the term limbic system to refer to the margin or edge which encircles the undersurface of the brain, as it is viewed following removal of brainstem and cerebellum.