The limbic system

Abstract

Byline: V. RajMohan, E. Mohandas hypothalamus, anterior thalamic nucleus, cingulate gyrus, hippocampus and their interconnections, constitute a harmonious mechanism which may elaborate functions of central emotion as well as participate in emotional expression. James Papez, 1937 The consists of phylogenetically old lobe and other subcortical structures and their connections. Although not empirically proven, is a functional concept which may be employed to explain various brain functions.[sup] [1] History Paul Pierre Broca in 1878 spoke of ' le grand lobe limbique' or great lobe and applied term (from Latin limbus for border) to curved rim of cortex which incudes cingulate and parahippocampal gyri. However, its putative role in emotion was elaborated by American physician, James Papez in 1937 in seminal paper titled 'A proposed mechanism of emotion'. This anatomical model is referred to as Papez circuit.[sup] [2] Yakovlev in 1948 proposed Yakovlev's circuit in control of emotion involving orbitofrontal, insular and anterior temporal lobe cortex, amygdala and dorsomedial nucleus of thalamus.[sup] [3] In 1952, Paul D. MacLean coined term limbic system to describe Broca's lobe and related subcortical nuclei as collective neural substrate for emotion.[sup] [1] MacLean was also instrumental in proposing and defining concept of brain. MacLean's evolutionary Triune brain theory proposed that human brain was in reality three brains in one: R-complex (reptilian complex), and neocortex.[sup] [4] The concept of has since been further expanded and developed by Nauta, Heimer and others. Components of Limbic System There is no universal agreement on total list of structures, which comprise system. The brain regions that constitute are: *Limbic cortex i. Cingulate ii. Parahippocampal *Hippocampal formation i. The dentate ii. Hippocampus iii. Subicular Complex *Amygdala *Septal area *Hypothalamus These structures form a complex network for controlling emotion.[sup] [5] Limbic lobe The lobe situated at inferomedial aspect of the[sup] cerebral hemispheres, consists of two concentric gyri surrounding[sup] corpus callosum. Broca proposed that larger outer gyrus[sup] be named[sup] gyrus and smaller inner one the intralimbic gyrus.[sup] The (limbic lobe) consists of the[sup] isthmus of cingulate gyrus, parahippocampal (both of which are continuous via a bundle of white matter called cingulum) and subcallosal area.[sup] [6] The cingulate (Latin = Belt ridge) dorsal to corpus callosum is heavily interconnected with association areas of cerebral cortex. The parahippocampal in medial temporal lobe contains several distinct regions, most important being entorhinal cortex (ERC). The ERC funnels highly processed cortical information to hippocampal formation and serves as its major output pathway.[sup] [5] The hippocampal formation Hippocampal formation in temporal lobe has three distinct zones: *The dentate *The hippocampus proper *The subiculum Embryologically, hippocampal formation is an extension of medial edge of temporal lobe. The entire hippocampal formation has a length of about 5 cm from its anterior end at amygdala to its tapering posterior end near splenium of corpus callosum.[sup] [5] Dentate The dentate is composed of three layers: an outer acellular molecular layer, a granular middle layer and an inner polymorphic layer. …