Amygdala Function and Location

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).

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 amygdala also ties 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.

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.

In This Article

Structure

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

The medial (middle) group of subnuclei which has many connections with the olfactory bulb and cortex (related to olfactory functions, or sense of smell).
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.
The central and anterior (front) group of nuclei has many connections with the brain stem, hypothalamus, and sensory structures.

Functions

The amygdala is an almond-shaped structure located right next to the hippocampus. The main function of the amygdala is in emotional responses, including feelings of happiness, fear, anger, and anxiety.

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 produce 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 within the formation of memories, especially those which 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 so is likely to be retained. Some emotional memories can be permanent, whereas those memories which 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, due to 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.

Neuroimaging

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 alike 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

A variety of research has shown that the amygdala, especially on the left side, are 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.

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 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).

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.

This fight-or-flight response is triggered by emotions of fear, anxiety, aggression, and anger. It is beneficial that the amygdala is working correctly in order 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 to be displayed.

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

Damage

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, leading 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 under active.

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 under active.

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 those 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.

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.

Deficits within the amygdala could result in anxiety disorders, addiction, depression, PTSD, OCD, and phobias.

There is no direct method to treat a damaged amygdala, however psychotherapy and medications can aid in some of the symptoms associated with the mental health conditions experienced.

Also, deep brain stimulation has shown promising results in helping to relieve some of the psychological and behavioral side effects such as hypervigilance.

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.

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

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.