The Amygdala: Definition, Function, & Location

By Charlie Huntington, M. A., Ph. D. Candidate
​Reviewed by Tchiki Davis, M.A., Ph.D.
The amygdala is a tiny brain region with outsized importance – it is the brain region that drives our experiences of fear, among other things. How does that work, exactly? Read on to find out.
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Do your eyes glaze over when people start talking about neurotransmitters, amino acids, and all these newfangled ways to fix different parts of your brain? I love psychology research, including neuroscience, but I have my limits, too. Sometimes the brain just seems like an impossibly complex topic for study, and as far as I can tell, that could be true: there are few things more complicated in nature than the human brain.
This is the dilemma we face when we try to understand how different parts of the brain work. None of them exist in isolation, and they communicate with and influence each other constantly. So what is the benefit of trying to understand different parts of the brain? I’ll try to make the case here that some aspects of our brains are fairly easy to understand, and fairly useful to understand, too. Let’s look at the amygdala – probably a brain region you have heard of before – and cut through the density of scientific research to get to the core of what this brain region is doing.
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What Is the Amygdala? (A Definition)

Close to two hundred years ago, a doctor dissecting a human body first recognized the region of the brain that would come to be known as the amygdala (Ledoux, 2007). Since this region was shaped like an almond, and about the same size, too, it was named after the Latin word for almond, which is, of course, amygdala.
 
It was originally thought that the amygdala was a standalone region of the brain, but researchers soon observed that it had closely related and nearby structures that seemed to be involved in the same activities. After this, a fierce debate raged about which parts of the brain were close enough in proximity and in function to count as part of the amygdala. Instead of going into unnecessary levels of detail here about this scientific journey, I will just say that scholars eventually agreed to call the original almond-like shape, as well as some other adjacent brain parts engaged in very similar activities, the “amygdaloid complex”, or just ‘amygdala’ for short.
 
So to summarize, the definition of the amygdala is a tiny brain region that is highly involved in certain emotional and cognitive processes – more on those in a moment. This region is a very evolutionarily old part of the brain—it is involved in very “primitive” functions such as our sense of smell, but it is also highly interconnected with evolutionarily newer parts of the brain (Swanson & Petrovich, 1998).

Function of the Amygdala

The function for which the amygdala is best known is its role in fear conditioning (Janak & Tye, 2015). This means that it is highly involved in both the experience of feeling fear and the experience of learning to fear something. When we have an experience that frightens us, our amygdalae (that’s the plural of the word!) help the more complex regions of the brain, such as our prefrontal cortex, encode (a fancy word for remembering) this experience as something we should be afraid of. 

For example, when I was a child, another young boy waited around the corner of a playground structure and jumped out to scare me. For years afterward, I had a sense of fear when I approached similar playground structures. The information I was getting from my senses – the sight of the structure, for example – was being processed by my amygdala and interpreted as something to fear.

For a more in-depth explanation of how the amygdala is involved in our learning to fear things, I recommend watching this video:

Video: The Amygdala and Fear Conditioning

While fear conditioning is the best studied of the amygdala’s many functions (Ledoux, 2007), the amygdala is involved in many other emotion-related processes (Janak & Tye, 2015). It has become clear that the amygdala also fires – in other words, shows a lot of activity – when we have positive emotions as well as negative emotions, and when we see things that are rewarding as well as threatening (Baxter & Murray, 2002).

In other words, when we are motivated to move toward something or away from it, the amygdala is functioning as part of that process (Janak & Tye, 2015). It is also involved in our behaviors that seek to meet basic needs, such as seeking comfort, eating, and sexual activity (Ledoux, 2007). It even is activated in accordance with what we are paying attention to. So one shorthand that has been proposed is that the amygdala’s job is to notice when things are emotionally relevant to us (Ledoux, 2007).

Location of the Amygdala

The location of the amygdala helps explain why it is so closely involved in so many brain processes, and so important in general. The amygdala is located near the center of the brain, slightly below center and towards the back, next to the hippocampus and close to the brain stem. For this reason, it is called a subcortical structure and is part of the limbic system (Hajek et al., 2008). In this position, it receives a lot of sensory information from more primitive regions of the brain, such as the brain stem, and a lot of more complex inputs from the most highly evolved parts of the brain, namely parts of the prefrontal cortex.
 
To help us understand these flows of information, let’s picture activity happening in two different directions. Sometimes, when I am rock climbing, I get scared. My amygdala is taking in important information from my senses – the sweat on my brow, the feeling of fatigue in my forearms, the tiny size of the next handhold – and saying, in the language of brain signals, “this is a dangerous situation! Charlie is afraid!”
 
These signals are sent up to my prefrontal cortex, where my most complex thinking happens. Here, I do my best to evaluate the situation with logic. I may have certain thoughts, such as, “you have more strength than you think,” or “the rope will catch you if you fall.” These thoughts, as brain signals, get filtered back down the whole system – through my amygdala and out to the rest of my body. If the thoughts are successful at overriding my amygdala’s fear response, I may take a deep breath, relax as much as I can, and try to keep climbing. If the fear signal is too strong, my amygdala may drive the action instead, causing me to shout out a warning to my partner down below that they should be ready for me to fall.​

What Does It Mean to “Hijack” the Amygdala?

We like to say, colloquially, that our amygdala has been “hijacked” by something that happened. What we mean by this is that whatever just occurred activates the amygdala so much that we cannot respond except with intense fear. This could range from having a particular thought – “what if I left the stove on?” – to seeing our partner smile flirtatiously at somebody else or standing at the base of a mountain as an avalanche starts above you.

Using the word “hijack” makes it sound like we are out of control or being controlled by something else. I think that misrepresents the value of the amygdala taking over. If I hear a loud rumbling above me on a snow-covered mountain slope, I would rather jump into immediate movement than stop to debate the right course of action. So the amygdala aims to help us.

Disorders of the Amygdala

Neuroscientists long wondered whether having an abnormal amygdala – one that was different in size or activity – caused psychiatric disorders. At this point, it is thought that abnormal amygdala functioning is better understood as a result, not a cause, of psychiatric disorders (Hajek et al., 2008). So in this sense, there are disorders of the amygdala, because the typical person with several different kinds of psychiatric disorders will show abnormal amygdala functioning. For example, people with mood disorders – bipolar disorder and depression – have amygdala of different sizes from people without these disorders (Hajek et al., 2008). Their amygdalae also respond more strongly to events in their environment than the amygdalae of people without these disorders (Phillips et al., 2003).

Amygdala Damage

A tried-and-true method of learning how brain parts work is by studying what goes awry in the lives of humans and other animals when those brain parts get damaged. In the case of the amygdala, damage seems to change people’s levels of fear, as well as their drives for things like food and sex (Ledoux, 2007). Neuroscientists will also intentionally damage an animal’s brain to understand what damage at particular places will cause. For example, severing the connections between the amygdala and parts of the prefrontal cortex will make it difficult for an animal to recognize potential dangers in its environment. For example, a mouse with little amygdala connection may not cower in fear or move away from a cat that is introduced to its cage.

The Amygdala and PTSD

It appears that the amygdala is significantly changed in people who have posttraumatic stress disorder, or PTSD (Morey et al., 2012). The amygdala of a person with PTSD shows more activity in response to emotion-inducing images than the amygdala of a person without PTSD. People with PTSD have smaller amygdalae on average, too. At the same time, these phenomena are not worse in people with worse PTSD symptoms. This suggests that people with PTSD may have been more susceptible to strong reactions to stressful events in the first place.

The Amygdala and Anxiety

Since anxiety and fear are somewhat synonymous, it should not surprise us that amygdalae look different in people with anxiety. Similar to the amygdalae of people with PTSD, the amygdala of an anxious person is likely to be smaller and more reactive than the amygdala of a person without anxiety (Davis, 1992; Rauch et al., 2003).

The Amygdala and the Hypothalamus

The hypothalamus is often called the regulator of the body – it is where most of our automatic, unconscious processes take place (Buijs & Van Eden, 2000). The hypothalamus and the amygdala interact with each other in the process of managing one’s stress response; an overactive amygdala can impede the ability of the hypothalamus to perform its regulatory functions.

The Amygdala and the Hippocampus

The amygdala and the hippocampus are also very closely linked. They are located right next to each other in the brain, which makes sense when you consider how much they work together to create memories. Since the amygdala focuses on the emotional contents of a situation, and the hippocampus is the seat of memory formation in the brain, they interact to create emotionally-laden memories (Phelps, 2004). Early life experiences that are traumatic or fearful are especially impactful on this link between the amygdala and the hippocampus (McEwen et al., 2016).  ​

Articles Related to Amygdala

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Books Related to Amygdala​

If you’d like to keep learning more, here are a few books that you might be interested in.

Final Thoughts on the Amygdala

Perhaps you have read articles online or talked to friends or even healthcare professionals about what you can do to manage your amygdala. I think this is an admirable goal, but perhaps not the most effective way to think about how to get there. The absence of fear would bring us all sorts of very real, new problems. Also, we do not experience less fear by changing our brains – we change our brains by having new experiences.
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We can see this in therapy and in our daily lives. After a fall at the climbing gym, the best way for me to face down my fear of climbing is to keep going. In my interpersonal relationships, the only way for me to get past the fear of bringing up my own needs was to do it, and then see that the outcomes I dreaded – my friend will get angry and leave me! – were not going to happen. And psychotherapy is where we truly, although indirectly, work on the amygdala. Fear is the belief that something bad will happen, but every time we face something frightening in therapy, we break down that association a little bit. The amygdala’s response may just weaken a bit (Janak & Tye, 2015), creating more freedom in our lives. I hope you can gently and courageously face the fears you’ve been conditioned to have but that are holding you back.

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