Amygdala: What It Is & Its Functions

The amygdala is a complex structure of cells nestled in the middle of the brain, adjacent to the hippocampus (which is associated with memory formation). It is part of the limbic system and plays a key role in processing emotions and emotional reactions.

Key Takeaways

• The amygdala in the limbic system plays a key role in how animals assess and respond to environmental threats and challenges by evaluating the emotional importance of sensory information and prompting an appropriate response.
• The main job of the amygdala is to regulate emotions, such as fear and aggression.
• The amygdala is also involved in tying emotional meaning to our memories, reward processing, and decision-making.
• When it is stimulated electrically, animals show aggressive behavior, and when it’s removed, they no longer show aggressive behavior.

What Is The Amygdala?

The amygdala is primarily involved in the processing of emotions and memories associated with fear. The amygdala is part of the limbic system within the brain and is key to how we process strong emotions like fear or pleasure.

As the amygdala has connections to many other brain structures, this means it can link to areas in order to process ‘higher’ cognitive information with systems that control ‘lower’ functions (such as autonomic responses like breathing, touch, and sensitivity).

This allows the amygdala to organize physiological responses based on the cognitive information available. The most well-known example of this is the fight-or-flight response.

Amygdala’s Connections and Neuronal Circuits

The amygdala has widespread connections to various parts of the brain, allowing it to receive sensory information and influence responses. Its key connections include:

• Input from the sensory thalamus and sensory cortices (visual, auditory, somatosensory) – provides sensory information to the amygdala.
• Output to the hypothalamus and brainstem – allows emotional responses like fear and aggression.
• Bidirectional connections with the prefrontal cortex – integrates emotions, cognition, and decision-making.
• Bidirectional connections with the hippocampus – links emotions to memories.
• Output to the nucleus accumbens and ventral striatum – involved in reward processing.

There are two amygdalae in each hemisphere of the brain, and there are three known functionally distinct parts:

1. The medial (middle) group of subnuclei has many connections with the olfactory bulb and cortex (related to olfactory functions or sense of smell). It also connects with the hypothalamus for social and reproductive behaviors.
2. The basolateral group (basolateral meaning below and to the side) has several connections with the cerebral cortex, particularly the prefrontal cortex within the frontal lobes. This allows it to link sensory stimuli with emotional responses and memory formation.
3. The central and anterior (front) group of nuclei has many connections with the brain stem, hypothalamus, and sensory structures. It initiates physiological fear responses through these pathways.

What Does The Amygdala do?

The main function of the amygdala is in emotional responses, including feelings of happiness, fear, anger, and anxiety. It also plays a big role in the formation of memories associated with emotional responses.

Emotion Learning

The amygdala plays a distinctive role in mediating many aspects of emotional learning as well as emotional behavior. An emotion the amygdala is particularly responsible for is controlling fear.

Using Pavlovian conditioning can cause something called fear conditioning to occur. This is when an otherwise neutral stimulus is paired with an innately aversive unconditioned stimulus.

For example, producing a loud banging noise (aversive stimulus) each time a person is shown an image of a particular stranger’s face (neutral stimulus).

After repeated pairing of these two stimuli, the neurons within the amygdala will be conditioned to the change in stimuli, reflecting a conditioned fear response.

Therefore, we may expect that the person in the example would then become fearful of the stranger in the image due to being conditioned to be fearful.

Literature supports the view that the amygdala has an influence on cognitive processes such as memory formation, decision-making, attention, and social behavior.

It can be assumed that this is due to the amygdala projecting information to the prefrontal and sensory cortices, as well as the hippocampus. Thus, the amygdala can attribute emotions to these cognitive processes.

For instance, we may make a decision that is based on our own personal emotions, or we may pay more attention to something if we believe it will make us feel positive emotions toward it.

Memory Formation

An area in which the amygdala is most prominent is the formation of memories, especially those that are emotional.

As the amygdala is remarkably close to, and forms connections with the hippocampus (a memory structure of the brain), these two often work together to make memories more memorable.

The amygdala can attribute emotions to memories. Essentially, the more emotive the memory, the more likely it is to be remembered.

For instance, the birth of a child is typically a highly emotive positive memory, as it is likely to be retained. Some emotional memories can be permanent, whereas those memories that are mundane, having little to no emotional attachment, are often forgotten.

The amygdala acts as a store for good and bad memories, but especially for emotional traumas. This is when the amygdala can be detrimental as these traumas will be especially difficult to overcome due to it being a highly emotional memory.

Individuals who have experienced emotional trauma may also find that their trauma can affect other cognitive functions as a result of the amygdala being connected to many other regions of the brain.

Emotional memories are believed to be stored in the synapses of the neurons within the brain.

There is evidence that suggests that multiple neuromodulators in the amygdala regulate the formation of emotional memories (Tang, Kochubey, Klintscher & Schneggenburger, 2020). Fear memories are thought to be embedded within the neuronal connections of the amygdala.

Aggression

The amygdala is the most important part of the limbic system for many emotions, including aggression.

The reactivity of the amygdala is a good predictor of aggression. Groves and Schlesinger (1982) found that surgical removal of the amygdala reduces aggression in previously violent individuals.

In animal studies, stimulation of the amygdala produces aggressive behavior. Removal of the amygdala from monkeys, rats, and humans reduces aggression.

Fear

The amygdala’s role in psychopathy has been a major topic of study in neuroscience for many years. Historically, the amygdala was believed to be the “fear center” of the brain, responsible for experiences and behaviors related to fear (Kiehl, 2006).

This belief was based on evidence from animal studies, studies of individuals with amygdala damage, and neuroimaging studies on healthy individuals (Maren, 2001).

Early theories linked psychopathy to a dysfunctional amygdala that resulted in reduced fear responses and impairments in associating actions with potential threats or punishments (Lykken, 1995).

However, newer research challenges the idea that the amygdala solely functions as a “fear center.” Some studies suggest that the amygdala may not be essential for the subjective experience of fear in humans (LeDoux, 2020).

Recent views propose that the amygdala is part of a larger network responsible for regulating bodily processes and representing affective states rather than specific emotions.

The current understanding of the amygdala’s function in psychopathy is not clear-cut. Neuroimaging studies have reported varied results: some found a negative association between amygdala activity and psychopathy, while others found a positive or no association (Sethi et al., 2018).

What Does The Research Say?

Many neuroimaging studies have investigated the structural and functional connectivity of the amygdala.

Social Behavior

Regarding social behavior, the basolateral part of the amygdala, which sends signals to the hippocampus, has shown it is able to modulate social behaviors in a bidirectional manner (Ada, Felix-Ortiz, & Tye, 2014).

The volume of the amygdala has also been shown to positively correlate to the number of social contacts and the number of social groups a person belongs to (Bickart, Wright, Dautoff, Dickerson, & Barrett, 2011).

Essentially, the more friends and friend groups someone has, the bigger their amygdala.

Sexual orientation

Sexual orientation has been suggested to be linked to structural differences in the amygdala. Homosexual males tend to show patterns in their amygdala similar to those of heterosexual females.

These two groups tend to have more widespread connections in their left amygdala.

Likewise, homosexual females tend to show patterns alike to heterosexual men and have more widespread right amygdala connections (Swaab, 2007).

Stress

Studies suggest that acute and chronic stressors are strongly associated with neuronal activity within the amygdala (Correll, Rosenkranz, & Grace, 2005).

Similarly, synaptic plasticity (the ability for synapses to strengthen or weaken over time) within the amygdala is implied to be affected by exposure to stress (Vouimba, Yaniv, Diamond, & Richter-Lerin, 2004).

Mental health disorders

Various research has shown that the amygdala, especially on the left side, is associated with mental health conditions such as social anxiety, obsessive-compulsive disorder (OCD), generalized anxiety disorder, and post-traumatic stress disorder (Arehart-Treichel, 2014).

People who have a severe case of social phobia show significant correlations with increased amygdala response (Phan, Fitzgerald, Nathan, & Tancer, 2006).

Also, those who have more neural pathways from their amygdala to their prefrontal cortex are more likely to experience nervousness and anxiety as these pathways allow the frontal cortex to be flooded with more alerts of threats from their amygdala.

Amygdala dysfunction may be associated with memory impairment in schizophrenia. Increased activity in the left amygdala was found to be negatively correlated with performance on an immediate memory task (Zheng et al., 2023). This links abnormal amygdala function to memory deficits in schizophrenia.

Individuals who are diagnosed with depression have been shown to have hyperactivity in their left amygdala, especially when interpreting emotions from faces, mainly fearful faces (Sheline et al., 2001).

Similar findings were discovered in another study with those who had PTSD. When they were shown pictures of faces with fearful expressions, their amygdalae tended to display high activation (Carlson, 2012).

In bipolar disorder, however, a study found that these individuals had substantially smaller amygdala volumes than those without bipolar disorder (Blumberg, Kaufman, & Martin, 2005).

Addiction

In terms of addiction, the basolateral amygdala has shown involvement in people relapsing when it comes to drugs.

Particularly, the amygdala integrates the influences of stress on drug-related memory (Wang et al., 2008). The amygdala has also been shown to be influential when it comes to internet addiction.

It was found that the functional connectivity between the amygdala and the prefrontal cortex was altered in those with internet addiction, concluding that this type of addiction may be associated with emotional disturbances and with the processing of emotions (Cheng & Liu, 2020).

Breathing regulation

New research has found that the amygdala plays a key role in breathing regulation and post-seizure apnea. The research found that seizures spreading to the amygdala can cause apnea during and after seizures (Harmata et al., 2023).

Stimulating a specific region of the amygdala could also induce prolonged apnea that persists after stimulation ends (Harmata et al., 2023). This suggests the amygdala is critically involved in seizure-related breathing issues.

Amygdala Hijack

The amygdala can be stimulated when faced with a perceived threat. If in a threatening situation, the amygdala will send information to other parts of the brain to prepare the body to either face the situation or to get away from it.

Emotions of fear, anxiety, aggression, and anger trigger this fight-or-flight response. It is beneficial that the amygdala is working correctly to act appropriately in threatening or stressful situations.

However, sometimes, the amygdala can act too strongly, leading to amygdala hijacking. Typically, in a stressful situation, the frontal lobes will step in to override the amygdala to ensure we respond rationally.

But, if the stressful situation causes strong feelings of anxiety, anger, aggression, or fear, this can result in illogical and irrational overreactive behaviors being displayed.

Essentially, the amygdala overrides the frontal lobes to hijack stress response control.

What Happens If The Amygdala Is Damaged?

If there are damages or differences in amygdala structure and function, one may experience one or more of the following symptoms:

• Difficulties with forming memories, especially those which would be emotional memories, due to the amygdala and hippocampus being connected.
• Overactive fear response or hypervigilance leads to interpreting many situations as threats and losing control over physical responses.
• Emotional sensitivity.
• Feeling anxious if there is hyperactivity of the amygdala or feeling little or no anxiety if the amygdala is underactive.
• Overly aggressive if there is hyperactivity of the amygdala.
• Feeling over irritable if there is hyperactivity of the amygdala.
• Deficits in recognizing emotions (especially fear) if the amygdala is damaged or underactive.

Patient SM

A famous case study of someone who had damage to their amygdala in both hemispheres is patient SM. SM had no visible motor, sensory, or cognitive deficits and was able to identify a series of facial expressions.

However, the one facial expression she could not identify was that showing fear. She could also produce drawings of every facial expression but could not draw a fearful expression and claimed she did not know what a fearful face would look like.

Impaired fear response

If the amygdala is damaged or not fully functioning, this can impair the acquisition and expression of fear learning. They may not learn from the Pavlovian form of classical conditioning as a result.

This suggests they are less susceptible to forming phobias and less likely to be an anxious person; however, they may not have a natural aversion to risk, and this can, therefore, impair their ability to make safe decisions.

Managing damaged amygdala

While there is no way to treat a damaged amygdala directly, psychotherapy approaches can help manage some of the resulting symptoms.

Cognitive behavioral therapy focuses on identifying maladaptive thought and behavior patterns and learning new coping strategies. This can help reduce anxiety, depression, and emotional dysregulation.

Exposure therapy slowly exposes a person to feared stimuli in a safe environment to help overcome phobias or overreactions.

Social skills training improves communication and relationship abilities impacted by amygdala damage.

Emotion regulation techniques teach how to monitor emotional responses and employ strategies like mindfulness or relaxation to maintain control.

Psychotherapy equips patients with skills to better manage their lives despite changes in emotional processing due to amygdala damage.

Medications may also be used to treat specific symptoms like anxiety, aggression, or depression that can occur. Deep brain stimulation shows early promise in modulating amygdala hyperactivity, but more research is needed.

FAQs

References

Arehart-Treichel, J. (2014). Changes in Children’s Amygdala Seen After Anxiety Treatment.

Bickart, K. C., Wright, C. I., Dautoff, R. J., Dickerson, B. C., & Barrett, L. F. (2011). Amygdala volume and social network size in humans. Nature Neuroscience, 14(2), 163-164.

Blumberg, H., Kaufman, J., & Martin, A. (2005). Amygdala and Hippocampal Volumes in Adolescents and Adults With Bipolar Disorder. Year Book of Psychiatry & Applied Mental Health, 2005, 31-32.

Carlson, N. R. (2012). Physiology of behavior. Pearson Higher Ed.Cheng, H., & Liu, J. (2020). Alterations in Amygdala connectivity in internet Addiction Disorder. Scientific Reports, 10(1), 1-10.

Correll, C. M., Rosenkranz, J. A., & Grace, A. A. (2005). Chronic cold stress alters prefrontal cortical modulation of amygdala neuronal activity in rats. Biological Psychiatry, 58(5), 382-391.

Felix-Ortiz, A. C., & Tye, K. M. (2014). Amygdala inputs to the ventral hippocampus bidirectionally modulate social behavior. Journal of Neuroscience, 34(2), 586-595.

Harmata, G. I., Rhone, A. E., Kovach, C. K., Kumar, S., Mowla, M. R., Sainju, R. K., … & Dlouhy, B. J. (2023). Failure to breathe persists without air hunger or alarm following amygdala seizures. JCI insight, 8(3).

Kiehl, K. A. (2006). A cognitive neuroscience perspective on psychopathy: Evidence for paralimbic system dysfunction. Psychiatry Research, 142(2-3), 107-128.

LeDoux, J. E. (2020). Thoughtful feelings. Current Biology, 30(11), R619-R623.

Lilienfeld, S. O. (1998). Methodological advances and developments in the assessment of psychopathy. Behaviour Research & Therapy, 36, 99–125.

Maren, S. (2001). Neurobiology of Pavlovian fear conditioning. Annual review of neuroscience, 24(1), 897-931.

Phan, K. L., Fitzgerald, D. A., Nathan, P. J., & Tancer, M. E. (2006). Association between amygdala hyperactivity to harsh faces and severity of social anxiety in generalized social phobia. Biological Psychiatry, 59(5), 424-429.

Salzman, C. Daniel (2019, February 27). Amygdala. Encyclopedia Britannica. https://www.britannica.com/science/amygdala

Sethi, A., McCrory, E., Puetz, V., Hoffmann, F., Knodt, A. R., Radtke, S. R., … & Viding, E. (2018). Primary and secondary variants of psychopathy in a volunteer sample are associated with different neurocognitive mechanisms. Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, 3(12), 1013-1021.

Sheline, Y. I., Barch, D. M., Donnelly, J. M., Ollinger, J. M., Snyder, A. Z., & Mintun, M. A. (2001). Increased amygdala response to masked emotional faces in depressed subjects resolves with antidepressant treatment: an fMRI study. Biological Psychiatry, 50(9), 651-658.

Swaab, D. F. (2008). Sexual orientation and its basis in brain structure and function. Proceedings of the National Academy of Sciences, 105(30), 10273-10274.

Tang, W., Kochubey, O., Kintscher, M., & Schneggenburger, R. (2020). A VTA to basal amygdala dopamine projection contributes to signal salient somatosensory events during fear learning. Journal of Neuroscience, 40(20), 3969-3980.

Vouimba, R. M., Yaniv, D., Diamond, D., & Richter‐Levin, G. (2004). Effects of inescapable stress on LTP in the amygdala versus the dentate gyrus of freely behaving rats. European Journal of Neuroscience, 19(7), 1887-1894.

Wang, X. Y., Zhao, M., Ghitza, U. E., Li, Y. Q., & Lu, L. (2008). Stress impairs reconsolidation of drug memory via glucocorticoid receptors in the basolateral amygdala. Journal of Neuroscience, 28(21), 5602-5610.

Zheng, G., Zhou, Y., Zhou, J., Liang, S., Li, X., Xu, C., Xie, G., & Liang, J. (2023). Abnormalities of the Amygdala in schizophrenia: a real world study. BMC psychiatry, 23(1), 1-9.

Further Reading

• Sah, P., Faber, E. L., Lopez de Armentia, M., & Power, J. M. J. P. R. (2003). The amygdaloid complex: anatomy and physiology. Physiological reviews, 83(3), 803-834. 
• Kim, J. E., Dager, S. R., & Lyoo, I. K. (2012). The role of the amygdala in the pathophysiology of panic disorder: evidence from neuroimaging studies. Biology of mood & anxiety disorders, 2(1), 1-17. 
• Ressler, K. J. (2010). Amygdala activity, fear, and anxiety: modulation by stress. Biological psychiatry, 67(12), 1117-1119. 
• Davis, M. (1992). The role of the amygdala in fear and anxiety. Annual review of neuroscience, 15(1), 353-375.