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The Amygdala - centre of Fear, Anger, Anxiety, and Aggression

This is the second of a 2-part series on The Amygdala - the part of the brain I think everyone should definitely learn more about.

 

In part 1, we covered 3 of the 5 key features of the amygdala:  1) That it regulates 4 important emotions - fear, anger, anxiety, and aggression 2) That it works automatically as an amplifier to make us take notice and react 3) It gets triggered very quickly, and sometimes inaccurately. Read more about Part 1 here

Here in part 2, we will finish covering the remaining 2 key features of the amygdala. Both of these features are intricately intertwined. 

There are some things we fear when born, there are some things we are born to fear, and there are somethings we learn to fear

Have you seen babies play with candle fires? Or attempt to cross the road even though there are moving vehicles? An alarming number of them don't seem too afraid. But once they have understood the danger, the fear stays with them throughout life.

Conversely, the number 1 fear around the world is either public speaking or spiders (depending on which survey you refer to). Again think about this: are babies scared of public speaking? Well, how can they be? They have no idea what is public or what is speaking! Haven't we all heard of babies blabbering loudly on a planeful of strangers? 

What about very specific fears? I know a guy who is fearful of wet-tissue. And as we covered the previous chapter, have you seen people screaming in fear while watching others on a roller-coaster? 

What's happening here?


 

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It turns out that there are different levels of fear.

 

There are some fears that seem innate, i.e. every human being has this fear when born. (You would appreciate that innate fears are not easy to test. Few ethics boards will approve experiments putting babies into a brain scanner and potentially scary situation.)

So far, the list of innate fears is a very short one. One widely accepted example is a sudden loud sound. At all ages, a sudden loud sound causes us to feel fear - this is true for a newborn baby, it is true for an adult watching a horror film, who knows to expect a loud sound to come, and yet still jump a little when it comes. 


A second but more disputed example is a fear of falling (note: not a fear of heights - but of falling from a height). This is shown in a visual cliff experiment. A baby is put on a chequered surface. The surface extends onto a piece of glass that covers a second chequered surface down below. As you can see from the picture, babies stop at the edge of the glass and do not dare to crawl across. They show some signs of discomfort, indicating some fear they would fall through (this also shows that babies are born with a sense of physics). The disputes lie in how strict the criterion for innate fear is - every human being must have the fear. Crucially, not all babies look fearful. Some seem puzzled or curious. 

 

Increasingly, what we realise is not that people are born with certain fears, but we demonstrate "prepared learning". In other words, almost all fears are learnt. But for some things, we learn to fear far more quickly and easily. 
 

The example of snakes highlights how this plays out in real life. Let's say a baby has never been out of the house and has never seen either a flower or a snake before (whether in real life or through a picture). You bring the baby out for the first time and there on a patch of grass is a flower and snake lying still. How do you think the baby would react? 

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Even though the baby has never seen either, almost all babies will have no fear of the flower but quickly and naturally develop a fear of snakes, a combination of their own sensing (this thing moves, and the tongue looks a little threatening) and their reading of the reactions of adults around them.

Crucially, there are some babies who never develop a fear for snakes, instead befriending them and keeping them as pets - you can find several examples of these on Instagram. Why does this happen? Ancient wiring - the collective experience of all past generations, seem to pre-empt us to be more sensitive to certain things. However, this predisposition can be altered by one's own personal experience - perhaps a visit to the reptile sanctuary with a really good guide, or a relative that happened to have a very gentle snake.

(Interestingly, scientists working with Rhesus monkeys have been able to condition them to fear flowers and not snakes)

This point on "prepared learning" - our inclination to fear certain things, is an important one, as we will see in our chapter on racism. 

 

Next, we move on to fears which are much more individualised, with a learning component that is obviously from personal experience. Joseph LeDoux demonstrates this with a simple experiment with rats:

  • Expose a rat to an innate fear - say an electric shock. What happens? The amygdala activates, and we observe the usual - heart rate and blood pressure goes, the rat expression changes, it releases stress hormones, etc.

  • Now suppose before an electric shock, we expose the rat to a ringing tone. So every time the tone comes on, you shock the rat.

  • What happens? When this is repeated many times over, the rat becomes conditioned to fear the tone. Just the tone alone causes the amygdala to trigger, and the usual stress and physiological reactions.
     

Great - this seems pretty obvious but the neuroscience behind it is interesting. It turns out that our amygdala has 2 distinct parts.

 

The first is the central amygdala that we have become familiar with - this is the part of the brain that triggers upon fear, anger, anxiety, and aggression - causes you to feel emotional. But there is a second part of your amygdala - the basolateral amygdala. If names are a turn off to you, the name is not important, the function is. The basolateral amygdala is the learner; it learns new fears through stimulus, either from the environment or other parts of your brain​. When these new fear stimuli are first received by your basolateral amygdala, it is not yet able to trigger your central amygdala. But over time, the neurons that are tagged to this particular stimulus start to build a strong network of synapses with neurons in your central amygdala, eventually gaining the capability to trigger fear. 


When the rat first hears the tune, the tune only registers in the basolateral amygdala. The rat is not fearful of the tone, only the shock. But over time, the association between tone and shock becomes so strong that the network between the basolateral and central amygdala is established. Eventually: 
 

  1. The rat can be fearful just by hearing the tone alone. Fear of something happening can trigger even if that something never happens

  2. The network between the neurons in the basolateral amygdala and the central amygdala can become so well established that the rat can become more fearful of the tone than the shock. We can become more fearful of something happening than the fear of that something itself. 

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Think about some of the fears we have in life. What exactly causes the fear? Is it actually doing something that scares us? Or is it the thought of it that scares us? Because the thought is merely the tone, the association. But if we become so fearful of just the tone, we might never try something, even if there was no shock. 

One last point:

How do we overcome our fears? How do we learn that something or someone isn't quite as scary as we had thought? 

Remember how we learn new fears, as we covered above? Neurons in your basolateral amygdala become sensitised to a particular signal, which then triggers your central amygdala.

 

Now what happens when a rat is constantly exposed to the tone, and there is no shock? And this happens 100 times, 1,000 times? Soon, the rat learns that the tone does not by itself cause any harm. This causes another group of basolateral neurons to register - when you hear this tone, it's ok, there's nothing to fear. 

Neurobiologically, what happens is that when the tone plays, 2 separate groups of neurons start to get active. One group wants you to be fearful, while the second group works to inhibit the first group from trigger the signal. This seems really weird - as if different parts of your brain are in competition with one another. But this is precisely how your brain works in many areas. Neurons don't just fire when there is a stimulus. Some neurons fire to prevent other neurons from firing. 

Over time, because the tone no longer leads to any pain, the first group of neurons weakens (the neurons themselves fire less readily; concurrently the synaptic network becomes less active, with some synapses dying out - if this sounds a bit alien to you, check out our page on neurons) while the second group becomes more established. The effect is that with enough time, you no longer feel fear.

There are a few major takeaways from this:

 

  1. You don't passively forget your fears. You actively learn that something isn't fearful.
     

  2. In this case, it's easy for the rat to learn that there's nothing to fear. The rat can physically experience if there is a shock or not. It's not quite so easy for many of our fears, which are at least in part manufactured in our minds. Unlike the rat, we don't know if there's really something to fear if we never dare to try something. A good way for us to tackle the possibility that our fears are self-manufactured is through fear-setting - an exercise from Tim Ferriss which I highly recommend
     

  3. Your brain is plastic - a term in neuroscience that means that it can be shaped and re-shaped. What used to trigger a big reaction can over time weaken until it no longer triggers. And you can learn to become more reactive to certain stimuli. You can unlearn old habits and learn new ones. You can change behaviour and personality. Your brain is very changeable
     

  4. While it is a new group of neurons in your basolateral amygdala that triggers to learn and unlearn fear, the basolateral amygdala doesn't work alone in this. The group of neurons which learns that something is not as fearful as original thought gets its inputs from another part of your brain - your pre-frontal cortex. And this segues nicely into our final feature about the amygdala: it doesn't work alone.

Your amygdala is influenced and influences many other brain regions

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The amygdala, like all other brain regions, is influenced by and influences many other brain regions. Each of the see interactions provides an added layer to how we see fear, anger, anxiety, and aggression play out in our lives:

 

Hypothalamus 

The hypothalamus is a very small region of our brain. But it plays an important role because it here that hormones or instructions for hormones are produced. These hormones act as amplifiers, getting other parts of the body involved quickly in response. What's an example? When you feel fear, your amygdala triggers the hypothalamus to produce Norepinephrine and Epinephrine - what we commonly know as adrenaline. These hormones make your heart pump faster and blood vessels dilate, allowing you greater capacity to run away.

Movement

We covered in the previous chapter the concept of the amygdala hijack. When there is a sudden need to decipher danger, the deciphering is done by the amygdala and not your cortex - amygdala deciphers quicker but less accurately. And as we also covered, if the amygdala does assess there is danger, there is a second hijack - instead of reporting danger to your frontal cortex to direct movement, the amygdala issues the order for movement itself. The speed at which your brain can direct you to get into action has kept us alive until now, although it regularly misjudges.
 

Ok, the boring stuff is out of the way. Movement and hormones, absolutely mechanical and mundane. Let's move on to some more exciting stuff.

Insular Cortex

The insular cortex activates upon disgust - both gustatory (what you eat) and moral disgust (when there is a violation of social norms). How this works is pretty interesting, you can find out more at the page on the Insular Cortex

What happens when your insular cortex triggers? One of the parts it immediately talks to is your amygdala. When you see something which is morally disgusting, it makes you angry or fearful. If it's a person that commits this morally disgusting act, you become more judgmental and harsher towards him/her. This has some roots in evolution. Social norms are the manifestation of some common understanding which everyone follows. Violation of these norms breaks this common understanding and introduces unfairness. Or it is an indication that you are not from our tribe, you are not educated in our ways, you are not one of us. You are one of them. 

Hippocampus

The hippocampus is the part of your brain that encodes new memory. Now let's go back to the example of rats, tones, and electric shocks.

Say you have 2 rat cages. When a rat is placed into rat cage A, a tone plays and the rat gets shocked. When the rat is placed into rat cage B, a tone plays and there is no shock.

What happens? Your (basolateral) amygdala learns about the stimulus - the tone that could lead to a shock. But it's your hippocampus that learns about the context - which cage is it that creates the shock. The 2 parts of your brain work together when both context and stimulus occur together (cage A + tone) and triggers your central amygdala to feel fear. If your hippocampus does not activate - you will not feel fear.

Now let's say you are alone in a locker room, and suddenly a group of male enter and assaults you. What happens? Fear and distress are triggered in your amygdala, who then screams out to your hippocampus - hey! Remember this. This is scary. This is dangerous. And the next time you enter a locker room alone, your memory brings back this incident, triggering your amygdala, causing you to feel fear.

This is an example of the bi-directionality of brain regions. The memory from the hippocampus can cause you to feel fear. But the fear in your amygdala can also cause your hippocampus to create and store a new memory.

One amazing thing your brain - it's pretty good at distilling what are the important details. Say locker room assault. Your hippocampus doesn't store useless information like what colour was the lockers or how many clothe hangers ou had in your locker. It remembers the important stuff. You can test this out for yourself. Remember 9/11 when the plane crashed into the Twin Towers? And it's scary and also makes some of us angry and anxious the next time we take a plane. But do you remember if there were clouds in the sky or was it a clear blue day? You don't - your brain has automatically filtered out the unimportant. Pretty impressive huh?

The interacion between emotions and rationality

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And probably the most important interaction - what is the relationship between our emotions and our rationality? How does the amgydala, the centrepiece of the emotional region of our brain, influence and is influenced by the rational region of our brain?

Find out more at our chapter on: Emotional vs Rationality

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