Motivation and emotion/Book/2014/Serotonin and emotion
What role does serotonin play in emotion?
Positive emotions are an important predictor for a healthy, long life . Negative emotions are associated with increased disease, depression and suicide (Young, 2007), so it is no surprise that the search for methods to fight this negativity is growing popular in today’s society. Serotonin, a neurotransmitter, has long been considered one of most influential factors affecting our emotions. Until recently, it was believed to hold the key to understanding emotion and treating depression. From this belief and interest we have developed medical treatments to alleviate symptoms of depression, including negative emotions. However, recent research could suggest something different. Serotonin may not play such a crucial role in emotion as once thought. This chapter will explore the relationship between serotonin and emotion and investigate how we can use current research to implement methods into our daily lives that could potentially increase our serotonin levels and/or positive emotions without the use of drugs.
Serotonin (5-hydroxytryptamine or 5-HT), often referred to as the ‘feel good’ chemical, is a monoamine neurotransmitter found in the brain, gastrointestinal tract (GI tract) and in blood platelets (Frazer, Maayani & Wolfe, 1990). Serotonin is created by a biochemical conversion process, beginning with tryptophan, which is a building component of protein. Tryptophan combines with tryptophan hydroxylase, which is a chemical reactor, to create 5-hydroxy-tryptamine (serotonin) (Frazer, Maayani & Wolfe, 1990). Approximately 80-90% of serotonin in the human body is found in the enterochromaffin cells in the GI tract, where it assists with intestinal movements. The remaining serotonin is created in serotonergic neurons of the central nervous system (Baganz & Blakely, 2012).
As a neurotransmitter, serotonin facilitates the movement of messages from one area of the brain to another and is understood to influence either directly or indirectly, most of our approximately 40 million brain cells (Borne, 1994). As serotonin circulates in such a widespread area, it is believed to affect a range of physical and psychological functions. This includes emotion, mood, sleep, sexual drive and function, temperature regulation, social behaviour, digestion, appetite and memory (Lesch, Wolozin, Murphy & Reider, 1993)cardiovascular system, muscles, endocrine system and other parts of the body (Berger, Gray & Roth, 2009).. Research also suggests that it could affect the
One of the most widely studied aspects of serotonin is its relationship with emotion and depression. Low levels of serotonin have been suggested as a possible predictor for depression, however it is not known if a serotonin deficit leads to depression, depression causes a decrease in serotonin levels, or neither (Young, 2007). Serotonin is still not fully understood. It is not possible to measure the levels of serotonin in the brain and therefore the exact function cannot be explained. (Young, 2007).
Emotion is described as a brief, subjective and conscious experience formed mostly by psychophysiological expression, biological reactions and mental states. It is believed to be influenced by mood, temperament, personality, disposition and motivation (Reisenzein, 2007). Emotion and its relationship with serotonin is widely studied, as well as its relationship with other neurotransmitters and hormones such as dopamine and cortisol. Although similar, emotions are different from feelings, mood and affect and can power both positive and negative motivation.
Emotion vs. similar constructs
Emotion can be defined differently from a number of similar constructs. This is important to understand as the theory and research is different for each construct.
Differences between emotion and feelings, mood and affect (Reisenzein, 2007).
|Construct||Difference to emotion|
|Feelings||best understood as a subjective representation of emotions, private to the individual experiencing them.|
|Moods||diffuse affective states that generally last for much longer durations than emotions and are also usually less intense than emotions.|
|Affect||an encompassing term, used to describe the topics of emotion, feelings, and moods together, even though it is commonly used interchangeably with emotion.|
The physiology of emotion is related to arousal of the nervous system with varying levels of arousal linking to a particular emotion. Emotions lead to physical and psychological changes and these changes influence our behaviour (Kleinginna Jr & Kleinginna, 1981). Although people who act largely upon their emotions may be viewed as though they are ‘not thinking’, it is impossible to feel an emotion without cognition. For example, the emotion of fear will usually be a response to feeling threatened. Cognition of a threat and arousal of the nervous system, such as a rapid heartened, sweating and muscle tension, is an important element of the understanding and labeling of that arousal as an emotive condition (Kleinginna Jr &Kleinginna, 1981).
Five elements make up Scherer’s components processing model of emotion (1984). From his perspective, all elements must correspond and synchronize for a brief period of time for an emotion to take place. The cognitive appraisal is controversial as some believe that cognition and emotion are divided yet related structures (Sherer, 2001). However, the components processing model of emotion offers an effective description of the events that occur during an emotional response.
Scherer’s components processing model of emotion (1984)
Theory and research
Perform a quick internet search and you will find an abundance of material from thousands of different sources discussing the relationship between serotonin and emotion. As a topic common amongst popular culture, guidance and advice based on false facts and myths is readily available. It is important to understand what we know at the role serotonin plays in emotion to effectively recognise incorrect information.
Do high serotonin levels create positive emotions and low levels create negative emotions?
Some believe that serotonin is one of the central influences and causes for our emotions. Currently, the strongest evidence suggesting serotonin influences our emotions is findings from studies on the link between serotonin and depression. It is believed that medications which increase levels of serotonin, such as an SSRI, lead to alleviated symptoms of depression, which includes negative emotions (Shapr & Cowen, 2011). Studies on genetics have found a link between serotonin and depression, and therefore possibly emotions (Hariri & Holmes, 2006). One study discovered that a variation in the serotonin transporter gene creates a vulnerability to depression including negative emotions (Elay et al., 2004). However, this evidence cannot be confirmed as it is not possible to measure serotonin levels in the brain. Although serotonin levels in the blood can be measured, it is unknown if this is a reflection of levels in the brain (Young, 2007).
Depression is an illness with a biological basis that has social and psychological implications on your physical and mental health. The illness is characterized by low moods, negative emotions, and feelings of guilt and unworthiness (Who.int, 2014). It is the leading cause of disability worldwide (Who.int, 2014), with approximately 1 million Australian adults currently suffering from depression (Beyondblue.org.au, 2014). Although it is not known exactly what causes depression, it is believed to be related to an imbalance of neurotransmitters, such as serotonin, or hormones (Young, 2007). Although researchers have found a link between serotonin and depression, this relationship remains unclear:
Do low levels of serotonin lead to depression or does depression cause a decrease in serotonin?
Currently, it is not possible to extend our knowledge as we cannot measure serotonin levels in the brain (Archer, 1997).
Selective serotonin re-uptake inhibitors (SSRIs)
Several methods of treatment exist for depression including various medications that are understood to affect the function of certain neurotransmitters and hormones. Selective serotonin re-uptake inhibitors (SSRIs) are one of the most common medications prescribed to manage the symptoms of depression.
Although it remains unclear, it is believed that SSRIs are effective in the treatment of depression as they increase the level of serotonin in the brain and therefore lead to the alleviation of symptoms including negative emotions (Young, 2007). However, controversy has risen from evidence suggesting that SSRIs could be a little more than just a placebo with side effects. The truth is, we don’t really know how SSRIs work. Re-uptake is the process where neurotransmitters are naturally absorbed back into the nerve cells in the brain. A reuptake inhibitor, such as an SSRI, prevents this from occurring. Rather than reabsorbing, the neurotransmitter remains briefly in the synapse, which is the area between each nerve. This appears to create higher levels of serotonin, which leads to better communication between nerve cells and therefore strengthens the parts of the brain which controls emotion and mood (Ciraulo, N.D).
MDMA, or 3,4-methylenedioxy-N-methhylamphetamine, is a neurotoxic (toxic to the nerves) and empathogenic (produces specific social and emotional effects) drug that is part of the phenethylamine and amphetamine classes of drugs (Curran, 2000). MDMA often goes by the street name 'ecstasy' or 'molly' and is an illegal, popular recreational drug with users reporting feelings of euphoria and an increase in sociability and positive emotions (Curran, 2000). The drug is believed to work by affecting the activity of several neurotransmitters in the brain, primarily serotonin. MDMA triggers the release of enormous amounts of serotonin which is believed to be the reason that users experience intense feelings of happiness and increased sociability and empathy. These effects usually last 3 to 8 hours, which is how long your brain takes to naturally create serotonin and then destroy it with chemicals (Curran, 2000). When your brain is affected by MDMA, it creates more serotonin than usual, which means it also destroys more than usual. Therefore, when you brain is back to a normal state where it is not affected by MDMA, there is less serotonin binding to your receptors (Curran, 2000). This could lead to a drug ‘hangover’. Users of the drug have described this hangover as characterised by negative emotions and depression (Curran, 2000). Several animal studies have found that MDMA causes long-term damage to neurons containing serotonin and suggests the same for humans (Curran, 2000). Long-term MDMA users have reported experiencing depression and other impairments to their mental abilities, however measuring the damage caused by serotonin in humans is difficult. Recent image studies on the brains of MDMA users have revealed changes in emotion and other brain activity (Curran, 2000). Current findings on MDMA point to a strong relationship between serotonin and emotion. However, these findings cannot be confirmed and more advanced technology and research is needed to discover the accurate effects of MDMA on emotions and the brain.
Recently, scientists have discovered that serotonin may not play such a crucial role in our emotions as originally thought. People with depression have on average, a smaller hippocampus than people without depression (Kronmuller et al., 2008). The hippocampus is a part of the brain that is believed to control memory and emotion. When a person is under stress, the cells and networks literally deteriorate in this area (Kronmuller et al., 2008). It appears that the longer a person has had depression, the smaller their hippocampus will be. When we are able to regenerate the cells and networks, new neurons are stimulated, our hippocampus begins growing and our emotions improve (Kronmuller et al., 2008). SSRIs and other drugs which increase serotonin levels have an indirect affect on the growth of these brain cells. This could explain why medications which aim to boost serotonin increase positive emotions but not for the reasons originally thought. New research has found that increasing serotonin increases the release of other chemicals that stimulate neurogenesis, which is the growth of new neurons (Krenmuller et al., 2008). There is now growing support to focus anti depressant medications on neurogenesis, rather than increasing the levels of serotonin and other neurotransmitters (Krenmuller et al., 2008).
Another study investigated thistopic using mice . Researchers developed mice that were not able to create their own serotonin and ran tests to see if they would develop negative emotions and other symptoms of depression. The mice showed increased levels of compulsivity and aggression but not symptoms of depression. One test included putting the mice without serotonin and a control group of normal mice with serotonin under significant stress and found no difference in their emotions and behaviours. Both groups of mice also responded equally to antidepressant drugs which aimed to increase levels of serotonin. This study concluded that serotonin does not play a role in depression and therefore possibly emotion (Angoa-Perez et al., 2014).
Bananas and Turkey?
Eating bananas and other food high in serotonin is commonly believed to increase positive emotions. Food containing tryptophan, such as turkey, is also often advised as a serotonin and emotion booster. This could suggest a strong link between serotonin and emotion. Although the idea is popular, it does not hold merit. Purified trytophan may increase serotonin levels in the brain, however foods containing high levels of trytophan do not (Wurtman, Hefti & Melamed, 1980). Trytophan is carried into the brain via a system that is active toward large neutral amino acids. There is competition among the amino acids for the transport system and tryptophan, which is the least abundant amino acid, loses against its larger counterparts. After eating food containing protein, such as turkey, plasma levels that have risen in the other large amino acids prevent plasma levels rising in tryptophan, which prevents tryptophan from increasing in the brain (Young, 2007). Bananas, and other foods high in serotonin cannot influence serotonin levels in the brain or emotions as their serotonin cannot cross the blood-brain barrier (Young, 2007). Serotonin used by the brain must be created inside the brain. What this means is that the serotonin in bananas and turkey cannot increase the levels of serotonin and positive emotions in the brain because it physically cannot get inside (Young, 2007).
For the past 40 years, researchers, doctors, health and allied health practitioners and individuals from the general population with and without depression, have been interested in manipulating serotonin levels as they believe this will increase their positive emotions (Young, 2007). There is expanding awareness and interest in happiness, health and well-being so finding methods without prescribed medications and drugs is popular (Young, 2007). Happiness and well-being are recognised as protecting against psychological and physical health problems. Negative emotions and moods lead to negative outcomes and positive emotions and moods lead to positive outcomes including good health and longevity (Young, 2007). Several recent studies found that negative emotions were related to increased disability due to mental and physical disorders (Lenze et al., 2001), increased vulnerability to depression (Jeanne, Gross, Persons & Hahn, 1998) and increased risk of suicide (Stein, Apter, Ratzoni, Har-Evan & Avidan, 1998) while positive emotions work the opposite way and tend to protect against these results (Young, 20077). Judging from current research, it appears serotonin could have an affect on our emotions. Although this effect is likely only indirect, findings still hold enough merit to implement the following methods that could lead to an increase in serotonin levels, positive emotions and other health benefits.
Although bananas and other foods high in serotonin cannot directly increase serotonin levels, they may have an indirect effect as they are high in vitamin B6. Vitamin B6 is essential for your body to be able to create its own serotonin and a deficiency could mean a decrease in your natural serotonin production (Balk et al., 2007). Eating one medium sized banana will give you approximately 20% of your recommended daily intake of Vitamin B6 (Young, 2007). Other foods high in vitamin B6 include fish, chicken, beef liver and other organ meats, avocado, potatoes and other starchy vegetables, non-citrus fruits and fortified cereals such as Kellogg’s corn flakes and Special K (Young, 2007).
Another possible way to increase serotonin levels in the brain is exposure to light. This a treatment already used for seasonal depression/seasonal affective disorder (Young, 2007). A large quantity of research on a wide range of humans and mice suggests an interaction between light and the serotonin system. One study found that healthy women with tryptophan deficiencies, which is believed to cause negative emotions and moods, were able to completely obstruct this negative effect from occurring with a bright light (Bell, Abrams & Nutt, 2001). Simply spending more time in the sun every day could lead to increased positive emotions and serotonin levels as well as several other physical and psychological benefits (Young, 2007).
Exercise has a known antidepressant effect, with Austria and other countries prescribing exercise alone or alongside other measures as treatment for depression (Young, 2007). It is commonly believed that physical activity can increase serotonin function in the brain. One study claims that there are two mechanisms involved in the increase of serotonin through exercise. Firstly, motor activity increases the speed and amount of times serotonin fires in the brain, which sees an increase in the creation and release of the neurotransmitter. Secondly, exercising regularly boosts tryptophan levels in the brain (Dey, 1994). The way these mechanisms work is still not understood, however, it is strongly believed that physical exercise increases serotonin levels in the brain and therefore positive moods and emotions (Young, 2007). All types of exercise are beneficial for your physical and mental health and well-being, however aerobic activities are considered to be the most effective for increasing the creation of serotonin in the brain (Young, 2007). This includes walking, running, cycling and several other similar activities. This can be explained through the “runner’s high” phenomenon where a “feel good” effect is felt during and after exercise. This is believed to be the work of serotonin (Boecker et al., 2008). For better likelihood of increased synthesis of serotonin in the brain, it is recommended to exercise a minimum of 3 hours per week or 30 minutes six days a week, which can be separated into three 10-minute workouts per day (Young, 2007).
Test your knowledge
With growing interest in how to lead a healthy and positive life, society is constantly looking for ways to increase our positive emotions. To successfully manipulate our lives in a more positive direction, we must first understand our emotions and what controls them. Until now it has been the general consensus that serotonin plays a direct role in our emotions. Some recent literature believes that although the role is not as crucial as once thought, serotonin could have an indirect affect on our emotions. What must always be remembered is that science still does not know the exact role serotonin plays in our emotions and other parts of the human body. However, the methods discussed in this chapter may not only indirectly influence serotonin and our emotions but they have also been found to be directly linked with overall health. The evidence that does exist warrants further research in medicine, neurology and psychology to find what exact role serotonin plays in our emotions.
For more information on serotonin, emotion and similar topics please review the book chapters under ‘see also’. If you think you or a friend is suffering from depression or may be suicidal, speak to a trusted healthcare professional or call Lifeline on 13 11 14. Consult with your doctor first if you plan on starting any new diets or exercises.
- Dopamine and emotion
- Dopamine and motivation
- Depression and motivation
- Amygdala and emotion
- Happiness and health
- Testosterone and emotion
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