Emotions: Serontonin and the Limbic System

Running head: EMOTION: SEROTONIN, AND LIMBIC SYSTEM 1

Emotions: The roles of serotonin, and limbic system

University

EMOTION: SEROTONIN, AND LIMBIC SYSTEM 2

Abstract

This report will review how emotions control our behavior; focusing on serotonin physiology, and the role of the Limbic System. I will report the role of serotonin and physiological changes in the body affecting the emotions of an individual, as well as other symptoms that will be dully noted in the report such as depression. The Limbic System controls the physiological changes which affect impulse control, anger and aggression, among other emotions and behaviors--I will summarize the relation between activity and several disorders. Studies have been done to understand serotonin and physiology in humans, and medications that can increase serotonin activity to offset negative affects (Hariri and Brown, 2006, p. 12). This report will summarize the details of how serotonin, and how the Limbic System affects human behaviors.

EMOTION: SEROTONIN, AND LIMBIC SYSTEM 3

Emotions: The roles of serotonin, and limbic system

Emotions are generally defined as a state of mind that may reflect joy or fear, although, emotions also consist of patterns of physiological responses that lead to specific behaviors, which is what this paper will reflect. Specifically, the physiological responses of behavior are a direct reflection of how serotonin and the various areas of the Limbic System affect an individual. Imbalances of one or all three of these may constitute negative emotions such as fear, antisocial disorder, anger, poor impulse control, aggression, and depression. Research will show that emotions are not just a state of mind, but that behaviors are controlled by autonomic and hormonal responses that have biological significance.

Serotonin is a neurotransmitter, also known as 5-hydroxytryptamine, or 5-HT, is a hormone found in the brain, and is produced naturally in the pineal gland of the brain (Hariri and Brown, 2006, p. 12). A neurotransmitter is defined as specialized chemical messengers that support communication between nerve cells within the brain by conducting nerve impulses from one neuron to another. Some serotonin remains in the central nervous system while some flow through the blood stream to go to other organs. Inside the brain, neuronal clusters called raphe nuclei hold serotonin until its needed (Jonnakuty and Grangnoli, 2008, p. 303). Serotonin is necessary for your nerves and brain to work properly, regulate behaviors, and it has been shown to have an effect on mood (p. 303). Major components of the neural circuitry, including the primary regions of the brain associated with aggression, are now well established (Siegal and Douard, 2010, p. 23). In brief, the major sites of the brain where integration of this form of aggression takes place include the medial hypothalamus and the dorsal aspect of the midbrain periaqueductal gray matter (PAG) (Siegal and Douard, 2010, p. 23). It should be dully noted

EMOTION: SEROTONIN, AND LIMBIC SYSTEM 4

that it's possible that serotonin's effects upon aggressive behavior may occur by its actions on limbic structures such as the prefrontal cortex, which is know to powerfully modulate aggression and rage behavior (Siegal and Douard, 2010, p. 23).

Serotonin is often referred to as the "feel good" chemical in the brain that promotes happiness and wellbeing. Low levels of serotonin are often implicated in the pathophysiology of

psychiatric disorders ranging from depression, anxiety, and obsessive-compulsive disorders

(Jonnakuty and Grangnoli, 2008, p. 302). High levels of serotonin can cause behaviors of

restlessness and extreme agitation (p. 302). Pharmaceutical drugs known as selective serotonin reuptake inhibitors, or SSRIs, increase the level of serotonin activity in the brain and only enhance a signal that is already present in the same nerve that released it, but too weak to come through (Siegal and Douard, 2010, p. 21). One side effect of SSRIs is the potential for serotonin syndrome; is a potentially life threatening drug reaction that causes the body to have too much serotonin (p. 21).

One way to test the hypothesis that serotonin modulates aggression is to regulate the intake of dietary tryptophan, the amino acid precursor essential for the synthesis of serotonin and to then determine the effects of such manipulation upon aggressive behavior (Siegal and Douard, 2010, p. 21). Studies done on six healthy men and women showed that dietary depletion of tryptophan can, in fact, reduce serotonin levels in the brain (Siegal and Douard, 2010, p. 21). The study done on the men and women's estimated levels of brain serotonin levels were determined by lumbar puncture in which the serotonin metabolite in cerebrospinal fluid, 5-HIAA, was measured and provided empirical evidence that dietary alterations in levels of brain serotonin correlated with changes in aggressive behavior (Siegal and Douard, 2010, p. 21).

EMOTION: SEROTONIN, AND LIMBIC SYSTEM 5

Another study was noted in the aggressive behavior in women (p. 21). Findings reported that

women subjected to tryptophan depletion displayed elevated levels of aggression scores, and when tryptophan were increased there was a decrease in aggression scores (Siegal and Douard, 2010, p. 21). Thus, the studies provide support for the hypothesis that dietary induced reduction in brain serotonin is associated with increases in aggressive behavior (Siegal and Douard, 2010,

p. 21). A greater understanding of how serotonin affects the brain is something the medical and

scientific communities continue to explore, with hopes of improving targeted mental health

treatments that deal with mood disorders (p.

...