Stress Hardware Review: The Limbic System

Limbic-System The limbic system is the complex neuronal circuitry that controls emotional behavior and motivational drives. The good news: It comes preinstalled in your brain. The bad news: It controls not only behavior but also body temperature, the drive to eat and drink, and the ability to control body weight. The bottom line: Stressful emotions can set the limbic system on fire, causing overeating (or the opposite), sweating (or chills) and play funny tricks on the motivation to decide whether to fight the stressor, take flight from it or simply freeze in place. Let’s review this all-important structure in the management of stress.

Design

The limbic circuitry is located toward the front of the brain. The limbic system is comprised of numerous structures, the most important of which are the hypothalamus, the amygdala, the hippocampus, the cortex, the cingulate gyrus, the striatum, the pallidum, the thalamus, and Meynert’s nucleus basalis.

Features

The limbic system closely regulates behavior, and more specifically it determines the body’s initial and instinctive reaction to emotional challenges that influences the individual’s ultimate response. For the difference between reaction and response, see this post.

In addition to its primary role in behavior control, the limbic system controls many internal conditions of the body, such as body temperature, concentration of the body fluids, and the impulse to eat and drink, and thus the ability to control body weight.

Since the regulation of these functions is located within the same structure that also processes the first impact of emotions, it is easy to see how a stressor can immediately be felt as a loss of appetite in some of us, or a craving for “comfort” food in others. This design of the system makes it more difficult to keep one’s cool (temperature is affected, too) and to make clear-headed decisions in the face of a serious emotional challenge—exactly when such ability would be needed the most!  Be that as it may, our natural endowment consists of a circuitry that handles the rational and the irrational at the same time and within the same structure, so one must make the best of it in the face of challenges and stressors that can wreak havoc even on the best fine-tuned system.

Technical Specifications (if you really want know all about it)

| References | The outer arc of the limbic system (also called the limbic gyrus) includes the subcallosal area, the cingulate gyrus, the isthmus of the cingulate gyrus, and the parahippocampal gyrus, including the uncus and subiculum. The subcallosal area includes a cluster of small septal nuclei that lie immediately anterior to the paraterminal gyrus and anterior commissure. The septal nuclei receive input from multiple midbrain nuclei, the substantia nigra, the CA1 region of the cornu ammonis, the subiculum, amygdala, lateral hypothalamus, cingulate gyrus, and mamillary bodies. Efferent fibers project to the entire hippocampal formation, the habenula, hypothalamus, thalamus, amygdala, mamillary bodies and the cerebral cortex.

For even more detailed information on the septal region of the limbic system see this article: Cavazos JE, Wang CJ, Sitoh YY, et al: Anatomy and pathology of the septal region. Neuroimag Clin NorthAm 1997; 7:67-78.

br-800epi The middle arc (also referred to as Broca’s intralimbic gyrus) consists of the paraterminal gyrus, the indusium griseum, and the hippocampus. The paraterminal gyrus is wedged between the septal nuclei and the anterior commissure. Posterior to the anterior commissure is the hypothalamus. The indusium griseum, extending from the paraterminal gyrus, consists of gray matter and white matter tracts named the medial and lateral longitudinal stria. The indusium griseum is closely applied to the superior surface of the corpus callosum. Posteriorly, it courses around the splenium and inferiorly merges with the tail of the hippocampus.

The mamillary bodies, fornix, alveus and fimbria form the inner arc. The alveus and fimbria are the major efferent fibers tracts of the hippocampus. Posteriorly, the fimbria form the crura of the fornix that continue upward deep to the splenium of the corpus callosum. As the two crura converge, a thin triangular sheet of fibers passes to the opposite side to form the commissure of the fornix. The crura merge as the body of the fornix, which continues forward along the inferior edge of the septum pellucidum and roof of the third ventricle. At the foramen of Monroe, the fornix divides into two columns which course inferiorly. Just superior to the anterior commissure, the columns divide into pre- and postcommissural tracts. The precommissural fibers connect to the septal nuclei and anterior hypothalamic nuclei. The postcommissural fibers continue inferiorly to end in the mamillary bodies.

Need still more details? See this comprehensive article: Sitoh YY, Tien RD: The limbic system: An overview of the anatomy and its development. Neuroimag Clin North Am 1997; 7:1-10.