Limbic System

Reacting suddenly to a strong emotion can feel instinctive, something that you have little control over at that moment. But what causes this reaction? Scientists believe that the limbic system in the brain is responsible for behaviour related to strong emotional reactions. The limbic system explanation will explore the function and structures of the limbic system, plus associations with aggression

Limbic System Limbic System

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Table of contents
    • First, we will examine the limbic system function.
    • Then we will look at the limbic system structures.
    • Followed by a labelled limbic system diagram.
    • After we will explore more in-depth some of the limbic system parts.
    • Finally, looking into aggression and the limbic system.

    Limbic System, simple illustration of the limbic system, StudySmarterFig. 1: The limbic system is involved in a variety of processes¹.

    Limbic System Function

    Papez suggested in 1937 that the connecting circuit of the hippocampus and the limbic lobe was responsible for emotion (named the Papez Circuit).

    MacLean later expanded this idea and redefined it as the limbic system. It was assumed that the processing of information is a hierarchical system: Information is received and processed first by the lower elements of the limbic system. Then the higher cognitive elements of the limbic system process the information to enable a sufficient response.

    Overall, the limbic system functions can be seen as the reactionary system to a perceived threat within the environment but it is also heavily involved in other fundamental processes, such as memory.

    Initially, it was associated with smell, but it has been highly linked with the autonomic nervous system (ANS) and the endocrine system after much research.

    Limbic System Structures

    The higher limbic system structures comprise the following subcortical areas of the brain, amongst others:

    • The Hypothalamus is important in regulating the autonomic nervous system (ANS), and regulating emotional responses. It is integral to maintaining homeostasis in the body and regulates hormones such as testosterone. It is the overseer of other brain regions, such as the pituitary gland. Damage here can cause inappropriate responses to perceived threats.

    • The Hippocampus is involved in forming long-term memories and learning and spatial awareness and navigation. Neurogenesis (turning stem cells into nerve cells) occurs here. Damage here can severely impair your memory.

    Those with Alzheimer's have atrophy of the hippocampus formation regions.

    • The Amygdala is the emotional centre of the brain that processes fear-inducing and threatening stimuli and how they are linked/associated with forming new memories. It integrates emotions with motivational behaviours. Damage here can lead to more aggressive behaviours, as there’s a loss of control over your emotions (the brain’s emotional centre is important in emotions, it seems!)

    Even the size of the amygdala is suggested to have an influence on aggressive behaviour. A significant negative correlation has been found between aggression and amygdala volumes. Participants with higher aggression scores had a 16-18% reduction in the volumes of their amygdala (Matthies et al., 2012).

    • The Cingulate Gyrus is vital in regulating aggression, emotional responses to pain, communication and maternal bonding, amongst other functions. The anterior cingulate gyrus is linked to Broca’s and Wernicke’s areas (involved in language comprehension and production). It is thought to aid the vocalisation of emotional responses.

    Limbic System Diagram

    Below is a diagram of the limbic system and the other nearby structures. It is quite a complex system, but once you become familiar with it, you can begin to pick out the key areas of the limbic system.

    Limbic system, a diagram of the structure of the limbic system, with the cingulate gyrus in the middle of the brain, which partially surrounds the hypothalamus, the amygdala and is next to the structure of the hippocampus, StudySmarter.Fig. 2: A diagram of the structure of the limbic system shows us where these important areas are.

    Can you spot the structures mentioned earlier? The hypothalamus, the hippocampus, the amygdala and the cingulate gyrus are the main structures in the limbic system.

    Limbic System Parts

    The limbic system is comprised of multiple areas of the brain, namely the amygdala, hippocampus, cingulate gyrus, hypothalamus, and other notable regions, such as the thalamus and septum. We will explore how areas of brain damage affect the limbic system and in turn its involvement with aggression.

    First, let's consider a few notable roles parts of the limbic system play in bodily responses.

    The fight or flight response: This response starts in the amygdala and is the first point of action in response to a potential threat. It sends a signal to the ANS so the body can react appropriately (by releasing adrenaline and noradrenaline).

    Boccardi et al. (2010) found that prisoners with a history of violent offences (aggressive behaviours) had abnormal hippocampal defects that affected autonomic modulation and abnormal fear-conditioning.

    Damage and Disorders: Depression and the Limbic System

    When damage to the limbic system structures occurs, several disorders can develop, depending on the specific areas of damage. Here is an overview of the potential disorders that can come about as a result of damage to the limbic system:

    • Depression.

    • Anxiety.

    • Schizophrenia.

    • Bipolar.

    • Anger management disorders.

    • Parkinson’s disease.

    • Post-traumatic stress disorder (PTSD).

    • Memory disorders (storage, forming new memories).

    As we can see, a wide range of effects can occur when the limbic system is damaged.

    Research from Spanhel et al. (2018) suggests that damage to the amygdala can impact the recall of flashbulb memories (these are autobiographical memories that are associated with intense emotions).

    Recall of flashbulb memories was consistently impaired for participants with damage to the right area of the amygdala. Highlighting the fact that damage can affect emotional regulation in many areas of human function.

    Aggression and the Limbic System: Research

    The limbic system has been linked to aggression in the following ways:

    • Kluver and Bucy (1939) removed the core areas of the limbic system in rhesus monkeys. Monkeys then went on to have issues and complete absences of responses with their emotions and motor functions when researchers showed them certain stimuli (specifically, stimuli meant to induce fear and anger), and their vocal functions.

      They also lost an understanding of their places in social hierarchies and were more aggressive to try and gain dominance even when it was inappropriate/ill-advised. However, one thing to remember is that although this study shows the importance of the limbic system in affecting emotions, particularly aggression, we can not conclusively say this is comparable or applicable to humans. We deal with aggression differently (socially and culturally, as well as mediation tactics) to rhesus monkeys.

    • Groves and Schlesinger (1982) surgically removed the amygdala to reduce aggression in violent individuals. However, upon removal, individuals were reported to have lost their sense of emotion altogether. This finding suggests that the amygdala is involved with aggression and other emotions, and that emotion regulation is not a direct cause.

    • Gospic et al. (2011): In this study, two participants, the proposer (P) and the responder (R), played the Ultimatum Game. In this game, the proposer offers to split money either fairly or unfairly with the responder. If accepted, the money is divided as suggested. If rejected, both parties receive nothing.

      • They had their brains scanned by an MRI during the game, which found a heightened amygdala response to rejected, unfair offers, more noticeably in males than females.

      • If the participants were given anti-anxiety drugs beforehand, the amygdala had a decreased response, and unfair offers were less rejected. Overall, this suggests the amygdala plays an important role in processing and mediating emotional behaviour, particularly aggression.

    • Phineas Gage: In the case of Phineas Gage, he suffered extreme frontal lobe damage after an accident occurred whilst he was working. A metal rod went through his skull and damaged most of his frontal lobe, affecting his prefrontal cortex, which is linked to the regulation of emotional behaviours.After the accident, despite surviving such an injury, Phineas lived for another 12 years. However, his friends noted he was more aggressive afterwards. With the damage, his prefrontal cortex could no longer regulate his behaviours and inhibit the amygdala, so he had an unjustified and unregulated response to what he perceived as threatening situations.

    • Chang and Gean (2019) found that stress in socially isolated mice activates the ventral hippocampus (vHip) neurones, which induces attack-like behaviour (aggression). These neurones, which project into the ventromedial hippocampus, induce aggressive behaviour and can be inhibited to reduce it. This finding suggests that the above systems are involved in aggression overall.

    Limbic System, white gloved hand holding a white baby mouse, StudySmarterFig. 3: A study found regions of the brain in mice were associated with aggression.

    However, issues exist in that:

    • Links are only correlational: Research suggests there’s a link. However, some of the studies mentioned above only show a correlational link between aggression and the limbic system. It is not a direct cause, as seen in the case of Groves and Schlesinger. Similarly, in the ultimate game study, the amygdala only showed a faster, increased activation. It does not mean that aggression is coming from the amygdala directly, only that it is linked.

    • Cause aggression or abnormalities?: The abnormalities in the limbic system may cause increased aggression. However, increased aggression may also cause abnormalities within the limbic system. There’s no significant evidence to suggest either interpretation is correct.

    • Beta bias: Multiple studies supporting the role of the limbic system, and in particular, the amygdala, have issues with beta bias (they generalise the study, which was performed on one sex, to apply to both sexes).

    • Wong et al. (1997): In this study, 20 repetitive violent offenders (RVOs) were compared to 19 non-repetitive violent offenders (NRVOs) from a maximum-security mental hospital. There were asymmetric gyral patterns at the temporoparietal region (essentially, different-sized areas) that were particularly common in RVOs and absent in NRVOs. Yet, this study cannot be generalised to both males and females, as it’s a small sample size and was only conducted on men.


    Limbic System - Key takeaways

    • The limbic system includes the amygdala, the hippocampus, the hypothalamus, and the cingulate gyrus, amongst other notable structures.
    • The amygdala is the brain’s emotional centre and is responsible for the initial fight or flight response. It is involved in how humans process events linked to fear.
    • The amygdala is usually a good predictor of any following aggressive behaviour after a threatening stimulus is encountered.
    • The limbic system is linked to aggression, as multiple studies show if it is damaged or even removed, aggression is affected. It also had an increased response to unfair situations. Removal of these systems can affect emotional responses, including motor and vocal functions/reactions.
    • However, studies have issues with beta bias, and the link is only correlational. We do not know if abnormalities in the limbic system are the result of increased aggression or if increased aggression is the result of abnormalities. If they are conducted on animals, they are not always applicable to humans.

    References

    1. Fig. 1: The limbic system by DataBase Center for Life Science (DBCLS), CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons
    2. Matthies, S., Rüsch, N., Weber, M., Lieb, K., Philipsen, A., Tuescher, O., ... & van Elst, L. T. (2012). Small amygdala–high aggression? The role of the amygdala in modulating aggression in healthy subjects. The World Journal of Biological Psychiatry, 13(1), 75-81.
    3. Spanhel, K., Wagner, K., Geiger, M. J., Ofer, I., Schulze-Bonhage, A., & Metternich, B. (2018). Flashbulb memories: Is the amygdala central? An investigation of patients with amygdalar damage. Neuropsychologia, 111, 163-171.
    Frequently Asked Questions about Limbic System

    What is the limbic system?

    Papez suggested in 1937 that the connecting circuit of the hippocampus and the limbic lobe were responsible for emotion (named the Papez Circuit). MacLean later expanded this idea and redefined it as the limbic system.

    Overall, the limbic system functions can be seen as the reactionary system to a perceived threat within the environment. Initially, it was associated with smell, but it has been highly linked with the autonomic nervous system (ANS) and the endocrine system after much research.

    Where is the limbic system located?

    The limbic system is located below the cerebral cortex and above the brainstem in the brain.

    What are the causes of aggression and violence?

    There are many different causes for aggression and violence, and it is subjective (dependent on the person). However, the reasons behind an aggressive response can be linked to the neural mechanisms and the hormonal mechanisms in the brain.

    What is the major function of the limbic system?

    The limbic system is involved in our behavioural and emotional responses, such as fight or flight responses.

    Which organ is the limbic system?

    The limbic system is located in the brain, and 

    its structures comprise of the following subcortical areas of the brain, amongst others:

    hypothalamus, hippocampus, amygdala, and cingulate gyrus.

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    Team Limbic System Teachers

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