Studies of the regulatory functions of the limbic cortex

Abstract

1. 1. Stimulation of the anterior limbic area, and infra-limbic area, can produce three general types of changes in electrical activity. These responses have in common: that they can occur in all areas of cortex bilaterally at the same time; that they occur immediately when elicited by electrical stimulation; and that they act via cortico-subcortical mechanisms. The types of changes in electrical activity affected are: 1.1. (a) Attenuation. 1.1.1. (i) Decrease in voltage without change in pattern. 1.1.2. (ii) Decrease in voltage with decreased number of bursts or with simplification of burst patterns. 1.2. (b) Augmentation of bursts. 1.3. (c) Activation or “arousal” responses. 1.3.1. (i) with decreased voltage. 1.3.2. (ii) with increased voltage. Subcortical mechanisms by which these effects may be produced have been suggested. 2. 2. The anterior limbic cortex (“24s”) cannot be accurately described as a “suppressor area” on the basis of its electrical properties. This is based upon two facts: 2.1. (i) That type of electrical response called “suppression” in the literature, and attributed to this area as a localizable property has been shown to be the phenomenon of spreading depression which has no such local characteristics. 2.2. (ii) Attenuation of cortical electrical activity (which differs markedly from the “suppressor” response described in the literature) can be evoked by stimulation of this area; but so also can the contrasting types of responses in electrical activity herein called augmentation and activation. The term “regulatory” seems to describe the functional properties of anterior limbic cortex better than “suppressor”. 3. 3. It has been suggested that intimate relationships exist between phylogenetically old areas of the brain, i.e. the “mesocortex” of the anterior limbic regions, the thalamic reticular system, and the reticular formations in hypothalamus, subthalamus and brain stem; all possessing important regulatory control of cortical electrical activity and function.