• :00Days
  • :00Hours
  • :00Mins
  • 00Seconds
A new era for learning is coming soonSign up for free
Log In Start studying!

Select your language

Suggested languages for you:
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

Serotonin Research

Why someone is aggressive is hotly debated in psychology. Many suggest the environment is the cause, whilst others highlight the role of biology in aggression. Can our biology cause us to be aggressive? If so, what parts of our biology are the cause of aggression? One argument focuses on the role of serotonin. Serotonin research examines the role of the…

Content verified by subject matter experts
Free StudySmarter App with over 20 million students
Mockup Schule

Explore our app and discover over 50 million learning materials for free.

Serotonin Research

Serotonin Research
Illustration

Lerne mit deinen Freunden und bleibe auf dem richtigen Kurs mit deinen persönlichen Lernstatistiken

Jetzt kostenlos anmelden

Nie wieder prokastinieren mit unseren Lernerinnerungen.

Jetzt kostenlos anmelden
Illustration

Why someone is aggressive is hotly debated in psychology. Many suggest the environment is the cause, whilst others highlight the role of biology in aggression. Can our biology cause us to be aggressive? If so, what parts of our biology are the cause of aggression? One argument focuses on the role of serotonin. Serotonin research examines the role of the neurotransmitter in aggression.

  • First, we will establish the function of serotonin.
  • Then, we will discuss the role serotonin has on impulsive behaviour.
  • Next, we will look at the effects of low serotonin vs aggression.
  • Then, we will explore the various pieces of serotonin research on aggression.
  • Finally, we will provide an evaluation of the role of serotonin on aggression.

Serotonin Function

To understand the research on serotonin, first, we need to establish what serotonin is.

Serotonin is a neurotransmitter (made from the amino acid tryptophan) that has multiple functions and effects on the brain. Overall, it is an inhibitory neurotransmitter.

Serotonin research shows how it is key in mood stabilisation, and it is also known for being the happy hormone. It aids in feelings of happiness you may have throughout your day and relaxation. It functions as a neurotransmitter in your central nervous system, and a hormone in your peripheral nervous system.

Serotonin Research Chemical form of serotonin StudySmarterFig. 1: Serotonin is a neurotransmitter.

Those who struggle with abnormal levels of serotonin, be that too low or too high, often have issues with mood disorders.

Common examples include depression and anxiety, and serotonin has also been implicated in mental health disorders such as schizophrenia.

Serotonin also helps in:

  • Sleeping.

  • Digestion/eating.

  • Healing wounds.

Serotonin levels affect your mood and other bodily functions. Normal levels of serotonin usually mean that you will feel relaxed, relatively happy and calm, and more focused. You will generally feel comfortable.

Depending on how drastically and how long serotonin levels change, problems can begin to arise. Simply having fluctuating levels is normal. Increases and decreases occur naturally, and they are why we can react to certain situations appropriately.

Serotonin levels affect sleep. For instance, serotonin is associated with melatonin synthesis, and it also reduces REM sleep (rapid eye movement sleep), which aids in the natural sleep cycle. In some cases, low levels of serotonin result in insomnia.

Serotonin research, a man asleep and a dogs face looking out from under a floral duvet, StudySmarter.Fig. 2 - Serotonin levels affect sleep.

Serotonin vs Impulsive Behaviour

As you can see, research on serotonin indicates it plays an important role in mood regulation. The orbitofrontal cortex (OFC) is associated with self-control and higher cognitive functions. Normal levels of serotonin in the OFC are a large part of the reason why you can inhibit impulsive behaviours. The OFC sends important messages to other areas of the brain, notably the amygdala, for emotional processing.

The amygdala (involved in the limbic system) is important in aggression, and if stimulated, it can induce aggressive behaviours.

If we connect all of this information, we can see that:

  • Serotonin is a mood regulator: it inhibits or dampens certain moods, in this case, aggression.

  • If serotonin levels are low in the OFC, impulsive behaviours are not regulated or inhibited.

  • In some cases, the amygdala may have been stimulated, and it will send aggressive impulses to the OFC.

  • If serotonin levels are indeed low, these impulses ARE NOT inhibited, and the person will act on these impulses.

Low Serotonin vs Aggression

When serotonin levels are low the OFC is unable to control these aggressive impulses coming from the limbic system. This is the serotonin deficiency hypothesis.

The serotonin deficiency hypothesis suggests that there are low levels of serotonin involved in mood disorders, such as depression and chronic angry behaviour.

The causes of serotonin deficiency can vary. Meta-analysis of serotonin research found a slight inverse correlation between serotonin and aggression, anger and hostility (lower serotonin shows an increase in aggression). However, there may be interactions from the environment or personality aspects that researchers also need to consider when completing serotonin research (Duke et al., 2013).

You may have come across the links between research on serotonin and depression. This is because depression, when you look at its basic components, is a mood disorder. Those with depression often show low levels of activity in serotonin pathways, which is why they have issues with feelings of sadness, hopelessness, and lack of motivation. Left untreated, this can result in depression.It’s why a lot of treatments for depression involve SSRIs: selective serotonin reuptake inhibitors. They keep serotonin in the synaptic clefts for longer (this is what we mean when we say reuptake inhibitors, they inhibit the ‘reuptake’ of serotonin), to increase the effects of serotonin overall.

When a person takes drugs involving serotonin, issues such as serotonin syndrome can occur. The person may feel confused and agitated, and have twitching muscles, amongst other symptoms.

Serotonin on Aggression

As serotonin plays an important role in mood regulation, it is important to understand the role this neurotransmitter plays in aggression. Consider the following studies linking serotonin, the limbic system and aggression:

Coccaro et al. (2007)

In this study, ten people suffering from intermittent explosive disorder (IED, a disorder associated with reactive aggressive behaviour where people are known to perform poorly on facial emotion recognition tasks) were compared with ten healthy individuals (the control group).

They were asked to react to emotional faces whilst being measured by an fMRI. The researchers measured and compared amygdala and orbitofrontal cortex (OFC) reactivity to faces.

  • The activation levels were then also measured against previous aggressive behaviours from the individuals.

  • Those with IED had exaggerated amygdala reactivity and diminished OFC activation to angry faces, compared to the controls. The findings show an amygdala-OFC dysfunction in response to processing angry faces, supporting the connection between the OFC and the amygdala.

Brown et al. (1979)

In this study, 26 military men who were struggling to settle into military life had their cerebrospinal fluid levels measured for certain factors, notably serotonin (5HIAA, where serotonin has been broken down). They had no history of major psychiatric illnesses, although they demonstrated issues with settling and personality disorders.

  • 5HIAA levels had a significantly negative correlation with a history of aggressive behaviours in these men. To put it simply, they had lower levels of this byproduct of serotonin being broken down.

  • These low levels indicate that there’s less serotonin in the brain, which, as previously established, could explain why they had a history of aggression.

Deneris et al. (2003)

In this study, the PET-1 gene was found to be associated with the neurone development of serotonin.

  • Mice lacking in the PET-1 gene had serotonin neurones that failed to differentiate, and any remaining neurones had issues with serotonin synthesis, uptake, and storage.

  • This resulted in the mice having anxious and aggressive behaviours, suggesting insufficient systems for serotonin production and function are key aspects of aggressive behaviours, at least in mice.

Delville et al. (1997)

In this study, they tested the effects of fluoxetine (a drug that inhibits serotonin reuptake) on hamsters, assessing aggressive behaviours such as biting.

  • They found that after taking fluoxetine, the hamsters took a long time to bite or act aggressively.

  • This suggests that when serotonin remains in the synaptic cleft for longer, it allows for heightened mood regulation. Specifically, it reduced aggressive behaviours.

However, this is not to say serotonin plays a purely inhibitory role in aggression. This can be seen in the MAOA gene.

Serotonin Research, a woman with medium length wavy red hair wearing red lipstick and a black and white striped top has her mouth open as if screaming out in anger, StudySmarter.Fig. 3 - Low serotonin is linked to aggression.

Evidence of a Relationship Between Serotonin and Aggression

It is important to evaluate the research on the relationship between serotonin and aggression to establish how reliable and valid it is to make assumptions.

Passamonti et al. (2012)

In this study, the diets of 30 random, healthy individuals were manipulated, with 19 being included in the study overall (after exclusion). They altered their serotonin levels through acute tryptophan depletion (ATD).

  • This was done by giving them amino acid mixtures with low levels of tryptophan, the building blocks of serotonin, on the serotonin depletion day. They were given the same mixture but with normal levels of tryptophan on the control day.

  • They were then asked to view emotional faces (angry, neutral, sad) whilst being scanned using an fMRI. This allowed them to see how different regions of the brain communicate with each other in reaction to the stimulus.

  • Researchers found that on serotonin depletion days, the low levels of serotonin resulted in weakened communication between the amygdala and frontal cortex.

  • Those who were naturally more aggressive (established through a personality questionnaire) had an even weaker communication problem between these two areas.

  • Researchers suggest that these low serotonin levels are the reason why the frontal cortex struggles to inhibit and control the amygdala’s aggressive impulses. Without serotonin inhibiting the impulsive responses being sent, they reacted more aggressively to stimuli.

  • This study has high validity, as it used randomised participants and was a double-blind study.

Krakowski (2003)

Krakowski argued that it is difficult to establish a causal relationship between serotonin and aggression.

  • Overall, he suggested that the influence of serotonin in aggression depends on multiple factors, namely the individual's own self-control on their impulses, their emotional regulation, and the social situation at hand.

  • When dysfunction in serotonin occurs in aggressive individuals, whether this results in aggressive behaviours depends on individual differences and the social context the individual is in.


Serotonin Research - Key takeaways

  • Serotonin is one of the most well-known neurotransmitters and has multiple effects on the brain. It is key in mood stabilisation, and it is also known for being the happy hormone.
  • The orbitofrontal cortex (OFC) is associated with self-control and higher cognitive functions. Normal levels of serotonin in the OFC are a large part of the reason why you can inhibit impulsive behaviours.
  • The amygdala (involved in the Limbic System) is important in aggression, and if stimulated it can induce aggressive behaviours.
  • If serotonin levels are low in the OFC, impulsive behaviours are not regulated or inhibited when aggressive impulses are sent from the amygdala (serotonin deficiency hypothesis).
  • Crockett et al. (2012) suggested that low serotonin levels are the reason why the frontal cortex struggles to inhibit and control the amygdala's aggressive impulses.

References

  1. Duke, A. A., Bègue, L., Bell, R., & Eisenlohr-Moul, T. (2013). Revisiting the serotonin-aggression relation in humans: a meta-analysis. Psychological bulletin, 139(5), 1148–1172.
  2. Coccaro, E. F., McCloskey, M. S., Fitzgerald, D. A., & Phan, K. L. (2007). Amygdala and orbitofrontal reactivity to social threat in individuals with impulsive aggression. Biological psychiatry, 62(2), 168-178.
  3. Brown, G. L., Goodwin, F. K., Ballenger, J. C., Goyer, P. F., & Major, L. F. (1979). Aggression in humans correlates with cerebrospinal fluid amine metabolites. Psychiatry research, 1(2), 131-139.
  4. Hendricks, T. J., Fyodorov, D. V., Wegman, L. J., Lelutiu, N. B., Pehek, E. A., Yamamoto, B., Silver, J., Weeber, E. J., Sweatt, J. D., & Deneris, E. S. (2003). Pet-1 ETS gene plays a critical role in 5-HT neuron development and is required for normal anxiety-like and aggressive behavior. Neuron, 37(2), 233–247.
  5. Ferris, C. F., Melloni Jr, R. H., Koppel, G., Perry, K. W., Fuller, R. W., & Delville, Y. (1997). Vasopressin/serotonin interactions in the anterior hypothalamus control aggressive behavior in golden hamsters. Journal of Neuroscience, 17(11), 4331-4340.
  6. Passamonti, L., Crockett, M. J., Apergis-Schoute, A. M., Clark, L., Rowe, J. B., Calder, A. J., & Robbins, T. W. (2012). Effects of acute tryptophan depletion on prefrontal-amygdala connectivity while viewing facial signals of aggression. Biological psychiatry, 71(1), 36–43.
  7. Krakowski M. (2003). Violence and serotonin: influence of impulse control, affect regulation, and social functioning. The Journal of neuropsychiatry and clinical neurosciences, 15(3), 294–305.

Frequently Asked Questions about Serotonin Research

Serotonin is a neurotransmitter that acts as a mood regulator and has widespread inhibitory effects on the brain.

Serotonin can be triggered or released in several ways: through experiencing happy thoughts, memories, or events, through being in sunlight, and through exercise, to name a few. It is made up of tryptophan, which is found in nuts and red meat.

Yes, although it is gradual.

Depending on where in the body it is, serotonin can act as a mood regulator, and is important in feeling relaxed and happy. It also acts as a widespread inhibitor in the brain (as a neurotransmitter). As a hormone, it aids in eating, digestion, and feeling nausea, amongst other functions.

Through regulation of your moods (feeling relaxed, calm, and happy), this can result in you being able to focus more. This will then help you study.


StudySmarter is not a licensed medical practitioner. This information is for educational purposes only

Final Serotonin Research Quiz

Serotonin Research Quiz - Teste dein Wissen

Question

What is serotonin?

Show answer

Answer

It is a neurotransmitter in the central nervous system and a hormone in the peripheral nervous system.

Show question

Question

What is serotonin key in?

Show answer

Answer

Mood regulation and feeling relaxed, calm, and happy.

Show question

Question

What widespread effect does serotonin have on the brain?

Show answer

Answer

An inhibitory effect.

Show question

Question

What else can serotonin aid in?


Show answer

Answer

Sleeping, digestion, eating, healing wounds.

Show question

Question

What amino acid is the building block of serotonin?


Show answer

Answer

Tryptophan.

Show question

Question

How is the orbitofrontal cortex involved in aggression?


Show answer

Answer

When serotonin levels are normal, it helps inhibit impulsive, aggressive behaviours received from the amygdala.

Show question

Question

What happens if serotonin levels are low in the OFC?


Show answer

Answer

It cannot control or regulate impulsive, aggressive behaviours properly.

Show question

Question

What is the serotonin-deficiency hypothesis?


Show answer

Answer

Decreased levels of serotonin cause a reduced inhibitory effect, affecting the OFC and causing more impulsive and aggressive behaviours.

Show question

Question

What did Passamonti et al. (2012) find in their study?

Show answer

Answer

Lowering serotonin levels resulted in weakened communication between the amygdala and frontal cortex. Their studies suggest that low serotonin levels are the reason why the frontal cortex struggles inhibiting and controlling the amygdala's aggressive impulses.

Show question

Question

What did Coccaro et al. (2007) find?


Show answer

Answer

Those with IED had exaggerated amygdala reactivity and diminished OFC activation to angry faces, compared to the controls. The findings show an amygdala-OFC dysfunction in response to processing angry faces, supporting the connection between the OFC and the amygdala.

Show question

Question

What did Brown et al. (1979) find in their study?


Show answer

Answer

Low levels of 5HIAA were found in the spinal fluid of military men with aggressive behaviour tendencies. 5HIAA levels had a significantly negative correlation with a history of aggressive behaviours in these men. To put it simply, they had lower levels of this byproduct of serotonin being broken down.


Show question

Question

How is serotonin associated with melatonin?


Show answer

Answer

Serotonin is associated with melatonin synthesis.

Show question

Question

What can low levels of serotonin do to your sleeping patterns? 


Show answer

Answer

It can cause insomnia.

Show question

Question

What happens if you have normal levels of serotonin?


Show answer

Answer

You can feel relaxed and in control of your emotions.

Show question

Question

Do serotonin and aggression have a causal relationship?


Show answer

Answer

No, context matters. Both the individual and their social environment affect the aggressive behaviours, even with abnormal serotonin levels.

Show question

Question

What is the serotonin deficiency hypothesis? 

Show answer

Answer

The serotonin deficiency hypothesis suggests that there are low levels of serotonin involved in mood disorders, such as depression and chronic angry behaviour. 

Show question

60%

of the users don't pass the Serotonin Research quiz! Will you pass the quiz?

Start Quiz

How would you like to learn this content?

Creating flashcards
Studying with content from your peer
Taking a short quiz

94% of StudySmarter users achieve better grades.

Sign up for free!

94% of StudySmarter users achieve better grades.

Sign up for free!

How would you like to learn this content?

Creating flashcards
Studying with content from your peer
Taking a short quiz

Free psychology cheat sheet!

Everything you need to know on . A perfect summary so you can easily remember everything.

Access cheat sheet

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.

Start learning with StudySmarter, the only learning app you need.

Sign up now for free
Illustration