How does fear work in the brain?

28 October 2016

Interview with

Annemieke Apergis-Schoute, University of Cambridge

Horror films work by scaring us - but how does fear work in our brain, and how do Skeletonwe learn which things to be scared of? Annemieke Apergis-Schoute gave Georgia Mills a shocking demonstration.

Annemieke - So fear is a very essential emotion. It's thought to be one of the oldest emotions, as for any kind of organism it's important to be able to avoid threatening situations. So you have to know when you're in danger and then to avoid these areas or stimuli of danger.

Georgia - We've all been there. There's something in the corner of your eye. A door creaks... there's a shadow in the corridor. You start to feel scared, your heart rate increases, you start sweating, your muscles contract. This is what's known as the fight or flight response. Your brain has decided you're in trouble, sends out kind of an alarm call. And hormones like adrenalin flood your system gearing you up to get the heck out of there...  Turns out it was only the wind... big sigh of relief. But how do we learn which things we should be afraid of in the first place ideally so we don't jump out of our skin every time the wind blows.

Annemieke - What happens in the brain when you're learning about something new that's perhaps threatening, and you feel afraid because this stimulus is being paired with something aversive, we know that in the amygdala, which is a small almond shaped structure in the middle of the brain both of these stimuli come together. So all of your senses that take in what's happening in the environment, that gets transferred through sensory areas to the amygdala, and then also the input about the stimulus that it is of threat also gets into the amygdala. So, for example, if I was pairing a shock with a neutral stimulus, then something happens that's called associative learning and we know that this binding occurs in the amygdala, so the amygdala is central to learning about threat and, essentially, feeling fear in consequence for a certain stimulus.  

Georgia - Annemieke has a test she uses in her research, that lets you see your amygdala in action - it pairs a random stimulus - in this case a photo of an angry, green man, with an unpleasant result - in this case - a small electric shock.

Annemieke - Here you'll see two angry faces, and one of them might be followed by a shock while the other one is safe. And it would be up to you to figure out what's going on just by looking at the screen and then feeling when you get a shock and, at the same time, we record your skin conductance responses so we can see when you think you might be getting a shock. Because what will happen is your body will start to prepare for this shock and you will have little increases in skin conductance that we can see right here on the screen.

Georgia - Okay. So in response to being electrocuted by this machine, my amygdala will help me associate on of these scary faces with a nasty outcome and start to provide a fearful response which, I assume, is the sweating.

Annemieke - Exactly, yes. That's what you will be able to see.

Georgia - Well, I'm already nervous so let's give this a go. So I've got two sort of sticky pads with wires coming out of them on two of my fingers on my left hand.

Annemieke - Are you ready?

Georgia - Yeah.

Annemieke - Did you get a shock?

Georgia - No, I didn't get a shock from that angry green face.

Ohh yeah, it's gone off the charts there.

A red face now - no shock so far.

Oh no a green face.

Annemieke - It went up in preparation even though you didn't get a shock.

Georgia - I didn't get a shock. Ah, I see. So seeing that face...

Annemieke - So now what we can see in terms of fear learning is that every time you see the green face, we'll see a bigger increase in skin conductance than when you see the red face because you're starting to prepare for a possible shock. So after a couple of trials you will have figured this out and you'll see your skin conductance go up to it.

Georgia - Only one shock needed then before the mere sight of a green face instilled me with fear and my brain kindly got me ready to run away... not bad. But I also found that fearing something can actually help you cope with it because I stopped paying attention to the computer.

Annemieke - Fearing learning is almost instant. It was not even necessary to have a lot of these experiences and...

Georgia - Ahhh!!

Annemieke - I'll turn this off for you.

Georgia - Okay, thank you.

Annemieke - I think actually that you got an extra response because you weren't paying attention to it for a moment and then out of the corner of your eye you saw it again and right away got a shock. So it also shows you how being prepared can actually help a bit.

Georgia - Okay. Like you said - back to the evolutionary basis of fear - being able to predict when something is happening helps you a) avoid it and b) cope.

Annemieke - Yes, exactly. It is a good system. It's just that it can go out of order.

As you can see today, many politicians try to hijack this system as well by playing into our system of fear, and how we can so easily be manipulated to be afraid of things.

Georgia - Is there any evidence that what tends to frighten us changes as we age?

Annemieke - I think we habituate to a lot in the environment so, if anything, unless you develop an anxiety disorder, overall I think you'll become less and less afraid of stimuli in the environment. You just become more habituated to all kinds of things that can happen that are, in the end, not threatening.

Georgia - I mean I have a very strong memory of  being in the cinema - I think I was about seven - and I was watching Disney's Hercules. Not meant to be a scary film but I was terrified and ran out of the room when there was a monster.

Annemieke - Yes. I think that children, they also don't have this area of the brain called the prefrontal cortex yet which is involved in downregulating a lot of these responses. So also, when you're learning about something that it's no longer threatening, this area is very much involved in signalling that it has now become safe. And this area is not very developed in children, so it's very hard for them to learn when things are in fact okay, and things are not threatening, or to downregulate an emotional response. That's why I think they have, in general, all their emotions seem much stronger, not only the fear responses but also the happiness that comes out.

Georgia - When you go to the cinema and you see something a big scary, often when you get home at night you see it again and again, and when you're trying to get to sleep it's still there with you. What causes this sort of repetition of the spooky things you saw in the film.

Annemieke - What I think that happens, like I said before, you create a memory of this certain stimulus, or object, or scene that is threatening and because that's so active at that moment in your brain you're still processing it. A process called generalisation starts to happen, so if you've just been around loads of snakes, for example, and quite threatening ones, and then you go for a walk in the dark in the woods. And normally you might have a response to that as well, if you see the stick on the road and you might jump. But in that case you're primed, essentially, so your brain system that's involved in detecting things in the outside world, so a sort of a saliency network, is much more active I think at that moment to detect similar stimuli in the environment. So then I think you get some generalisation where you see things that look kind of like it and you system is already prepared to respond to it.

Georgia - And I suppose, that again, that is another result of evolutionarily it being handy for you to spot something that scared you recently?

Annemieke - Exactly, exactly.

Georgia - So next time you're being haunted by witches and ghouls after seeing a scary film remember, it's just generalisation. And it probably helped you ancestors from being munched on.

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