The limbic system and how to prevent it from making you join ISIS: Part 1

You may be thinking this is a bold title, and you’d be right (obviously). It’s going to take a whole lot of Cantatrice drivelling on about neuroscience while you, perhaps, smile and nod. But this is why you should bear with me (RAWR):

1: Neuroscience is hella interesting, and you know I’d only pull out the best bits to ram into your face.

2: The limbic system cannot be trusted. Do you want to join ISIS? WELL DO YOU?

But I gotta start with the limbic system: what it is, and the kind of bullshit it pulls.

When evolution went about building our brain from the first simple clump of neurons, through to our being the big-brained buggers we are today, it basically just kept slapping new stuff on top of the old stuff: above and forward, and above, and forward. The further back and down you go in the brain, the further back and down you go in time. Right at the bottom, the cerebellum and brainstem are sometimes called the “lizard brain” because we’ve had them a hell of a long time. They give us the really basic stuff: those body systems like our heart, lungs and digestion that we don’t control. We maintain consistent blood pressure and temperature; we get hungry and thirsty. It’s the dull but worthy bit of the brain.

Right at the front and top, we have the frontal cortex, which is the most recent development in our brain’s evolution. It’s where a great deal of reasoning and higher-level thinking goes on, as well as planning, impulse control and moral principles. This is the newest, shiniest and most human bit of the brain. Other mammals, especially primates, also have this structure (depending on exactly how you define it) but it’s most developed in animals that are smart and socially involved, and apparently we’re at the top of that list.

And between these is a layer of brain that we share with our mammalian ancestors who didn’t have such a developed cortex. If the modern frontal cortex is the place where – to quote Terry Pratchett – “the falling angel meets the rising ape,” then this layer is the place where the angry rat meets the other angry rat, smashes its face in and steals its cheese. The best part is the limbic system, which is the most amazing bun fight you’ve ever seen in your life and I am here for that drama, people.(1)

Many of the more boring neuroscience nerds will tell you that the limbic system is all about the body’s emotional states. Don’t listen to those people. The limbic system is like some kind of nightmare game show where each of the contestants is trying to smack a big button in the middle marked MANIPULATE MY BIOLOGICAL SYSTEMS! while also trying to prevent any of the other contestants from doing the same.(2) One bit wants to rile you up, another wants you to relax. One is obsessing over your new crush, and the hypothalamus is saying “oh fuck, I’m so horny. Or was it hungry? I don’t know. Maybe I should fuck a sandwich to be on the safe side.”

You’ve got the hippocampus, which is the memory centre of the brain. Memory sets up associations all over the brain, but it’s the hippocampus that picks them all up, sets them in some kind of order, stamps “DONE” on them and shoves them onto the shelf. Basically it’s the bit of the brain that makes memories behave like memories. The amygdala, which deals with emotional connections to the world around us, is right next to the hippocampus. If you’re like me and your amygdala is a little bit too keen, it may be extremely shouty, and respond to everything with AAAAAAAAAAAAAAAAAA. This is because it can get the ol’ fight or flight response going in an instant, as you’ll know well from those “is that an axe murderer?  No wait, it was a tree” moments. You’ve got the nucleus accumbens, which is the main pleasure and reward centre of the brain. You can help this guy win the round by feeding him any of the drugs that stimulate dopamine production, and most of the fun ones do. The nucleus accumbens is also involved in falling in love, personal accomplishment and in religious experience. I feel that his round in this game show has to involve some kind of WHAT’S BEHIND DOOR NUMBER THREE? Because let’s face it, if two of the options are Jesus and crack cocaine, it’s going to be difficult to look away. The basal ganglia are all about some of the more basic movement. You’ve got the olfactory bulb. Why the hell is smell buried down there next to the amygdala and hippocampus? Probably because it was very important to our ancestors. It’s that couple who bought their house 250 million years ago and intends to stay there forever, even as the neighbourhood gentrifies and all their neighbours start giving them snotty looks each time they pass. The other senses are close by, but they’re not mashed right up against memory and emotion like the olfactory bulb is. This is why, even though our sense of smell is really rubbish compared with other mammals, catching the smell of the face cream your dead grandmother used to use will fuck you up AND make you feel six years old again.

So as you can imagine, each time one of these contestants makes it as far as the button and smacks it down, the effect it has on our combination of body systems depends on who it is. But given how much bodily weirdness can ensue, it happens incredibly quickly. Something scares you, the amygdala gets in and slams the button, and suddenly your whole body is manipulated into doing weird stuff, from your heart and lungs going crazypants, to sweaty palms and nausea. In order to do this, the amygdala has to suppress the activity of its main opponent, the hippocampus. Have you ever studied really hard and then walked into an exam room and found you can’t remember a damn thing you learned because you’re too anxious? Yeah, this is what’s happening in the brain. The good news is that if you manage to calm down enough to get the hippocampus back at full throttle, it’ll come back.

Why am I telling you this? I will get on to ISIS eventually, I promise. At the moment, I’m showing some stuff about the limbic system because… well because I love it, really. But also because the idea many people have that learning and emotion are completely separate things is extremely wrong. You see, it’s a freaking mess in there. It’s all mushed close, all the bits are connecting to other bits, taking weird routes, and sometimes the messed up anatomy of it screws us over. The brain runs on neural connections and if two regions are mushed up against each other they will connect, and that may not work well for us.

Here’s an example. It’s fifty million years ago and you and your ratty bud(3) that you haven’t smashed in the face yet are out and about and he gets eaten by a snake. You didn’t like him much and now the snake’s eating him you can get away, but it’s all been a bit scary. The amygdala has been AAAAAAAAAAAAAAAAAAAing like a boss. The hippocampus has slunk off into a corner and now evolution has a problem. It’s obviously a very good idea for you to have some memory of OMG SNEK so that you can avoid them in future. But without the hippocampus how will you remember? I WILL TAKE OVER says the amygdala. I WILL REMEMBER THIS TERRIFYING MOMENT WITH THE HELP OF THE OLFACTORY BULB! And so it does. The next time you’re out with another ratty bud, you smell a snake, the amygdala starts the AAAAAAAAAAAAAAAAAA and you run the hell out of there leaving the other guy to his fate once again. SUCCESS!

Now we fast forward to you in your life as a modern day human. You’re out and about with a friend, and unlike rat-you, you actually like your companion. You’re in a deserted street, walking and chatting, when a man steps out of nowhere, grabs you by the hair, breathes down your neck and and points a gun at your head. He demands your friend hand over his valuables. He does. The robber lets you go, but as you’re stepping away your friend makes a grab for the gun. The robber shoots him and then flees the scene, and before you can get assistance, your friend dies.

Like your rat ancestor, you’ve made it alive through a dangerous situation that killed someone you were with. And as with your rat ancestor, your limbic system has it all set up to handle this shit. The amygdala goes AAAAAAAAAAAAAAAAAAAAA and you’re in fight or flight mode immediately, although as it happens neither option was all that helpful here. The hippocampus has slunk off into a corner. Who will remember the day of OMG MURDRR? The amygdala, once again! With the help of that old trouper the olfactory bulb!

If you think this is going to work out less well for human you than it did for Ratrick, you are correct. The first problem comes when you’re talking to the police. The amygdala puts down memories, but in a different way from the hippocampus. These memories are focused on the immediate source of danger, which makes sense if you want to avoid a particular species of snake. But in this scenario, your memory centres on the gun. Not the man holding it: his face, build or clothes just aren’t recorded. And definitely not little inconsequential details like which cars were parked nearby. In fact, since the hippocampus, which would have remembered your location, wasn’t doing its job, you might even be wrong about where you were at the time. But what’s worse is that you think you do remember these things, and you’re wrong: the brain has responded to gaps in your memory by shoving in details that could have been there, but weren’t. Witness testimony is staggering in its unreliability, but especially when it uses memories put down by the amygdala. Everyone from the police to the jury thinks that if a memory is vivid, and it makes a witness emotional, it’s more likely to result in accurate testimony. You yourself are convinced you remember, and you’re certainly emotional about the memories, because they come from the drama queen amygdala. But the memory is far more pliable than we think; it takes very little to send it off course. Line-ups are not a good way to catch the right person: we remember crimes badly, especially when we’re terrified, we tend not to remember the face of someone we’ve interacted with once, and the brain is prone to grabbing whatever information seems plausible and shoving it into hazy amygdaloid memories. Suddenly that guy who looks vaguely familiar is definitely the murderer. He isn’t; he’s just someone you’ve seen around town, but the familiarity pushes him into the memory and depending where you live he may end up executed because of your mistake.


So let’s stop here and I’ll be clear about what I do and don’t mean. I am not trying to claim that victims commonly invent a crime when there wasn’t one. The memory is easily manipulated, but it’s easily manipulated in ways that, these days, scientists understand pretty well. The problem is that lay people don’t, and the criminal justice system hasn’t caught up with all sorts of science, including this stuff. If someone tells you that they were raped on Friday night, there’s a very strong likelihood they’re telling the truth. If they say that they know the rapist (and most victims have at least met their rapist before) they’re almost certainly correct about who it was. They’re not going to accidentally sub in one of their work colleagues when it was actually next door’s gardener. No, there is no mechanism by which some silly little woman comes to the conclusion that she’s been raped when nothing happened. Now you may return to your Jordan Peterson videos while I speak to the grown ups.

Here’s the kind of situation where it can go badly wrong. In 1984, a stranger broke into Jennifer Thompson’s house and raped her. In the investigation that followed, she identified a man named Ronald Cotton as her attacker: first from a photo and then from a lineup. The case went to court and Cotton was convicted. After eleven years in prison he was exonerated by DNA evidence which linked a different man to the attack. Since then, Thompson and Cotton have become friends and now give talks together about the limits of eyewitness testimony. So what happened? Memories formed during extreme stress are more vivid and convincing than other memories. Thompson was absolutely certain that Cotton was her attacker, and said so repeatedly. She wasn’t lying. But these memories are also less reliable, more open to wobbling off in the wrong direction, grabbing other stuff in the brain and shoving it in there so that it becomes part of the memory when it shouldn’t be. Once an erroneous detail has made its way in it gets lodged. There are other factors, of course, that probably played into this miscarriage of justice.(4) Today, I don’t imagine a conviction would have gone through at all on the basis of witness testimony alone without DNA evidence.

But that’s just one way that the amygdala can fuck things up. Let’s return to the story of you, after you witnessed your friend get murdered. You know how I said that the hippocampus behaves like a librarian or archivist? This memory is created, stamped DONE, placed at this point in time, shoved back on the shelf where it can be accessed at will (to some extent, anyway). That isn’t how the amygdala works. It’s set up to fire off an OMG SNEK signal any time one is necessary, so it doesn’t need to place that memory of the snek in a clear place in the past. Sneks are an ongoing threat, right? They could be anywhere.

You discover the horror of this one evening when you’re out at a party, trying to move on with your life. But then you walk past some random guy, and he’s used the same shower gel as the murderer. Immediately the olfactory bulb alerts the amygdala which goes AAAAAAAAAAAAA SNEK SNEK SNEK SNEK and lobs the memory of your trauma directly at you in the hope that something in the memory will make you escape from this danger. You’re not in danger, but you can’t help but feel and behave as though you are.

That’s right. This mushy limbic system game show that worked out pretty well for Ratrick has gone and given you PTSD. Because the hippocampus isn’t holding the memory, it can’t file it away on the shelves marked SHIT WHAT HAS ALREADY HAPPENED, so it’s stuck there, spilled out on the table in front of you, in a sort of parallel timeline where other things are happening but also on the splitscreen your friend is being murdered over and over.

That’s not a fun way to live, so you go and seek help for your problem. Talking therapies can help. Meds can help. But one treatment that has become increasingly popular (albeit still a little controversial, because the body of peer-reviewed evidence isn’t really there at this stage) seeks to outwit the limbic system. To understand that, we need to look at the function of sleep. Sleep is still not fully understood: we obviously need it, but researchers are still figuring out why. One reason we do know about. The hippocampus likes to get its filing done when you’re asleep: more specifically that time called REM (rapid eye movement sleep) which is the bit where your eyes go bonkers under their closed lids, you dream, and the limbic system comes out to play. This memory consolidation is probably not the only function of dreaming, and it’s definitely not the only function of sleep, but it’s important for your psychological wellbeing.(5)

The hippocampus has a go at putting the memory of the murder away but it doesn’t work. Sometimes it tries again and again every night and you get recurrent nightmares. So sleep may not be something you look forward to, but this process that causes the nightmares has a key role in helping you get past them. EMDR (eye movement desensitisation and reprocessing) involves bringing the traumatic event to mind as a therapist does various exercises to get you to move your eyes about, looking in different directions. Demonstrating once again that the limbic system is very easily confused, the hippocampus sticks its imaginary head out, says “is this REM? Better get to work,” picks up the pieces of memory you’ve pulled out and starts to put them away. Incredibly, this seems to work: it takes an amygdaloid memory and turns it into a hippocampal memory. You remember the same basic facts but you don’t automatically trigger the SNEK SNEK SNEK response.

So that’s part 1 of this foray into the awesome world of neuroanatomy and its part in making teenagers join a cult, fight for ISIS, or become a big fan of Jordan Peterson. NEXT TIME ON THE NEUROSCIENCE WITH CANTATRICE SHOW: how this actually happens and how it can be avoided.

(1) It’s all a bit confusing, like everything else about the brain, and there are big fights over what everything does, and what the system is, and if there really is a limbic system anyway, and what should be in it, and why we can’t just call it the freaking NOZBRAIN like we used to because neuroscientists are a bunch of lil bitches except for Robert Sapolsky who is a precious cinnamon roll.

(2) What follows is an oversimplification of who all of these contestants are: brain functions typically take more than one region, and brain regions typically perform more than one function. But come on, I am literally talking about rats, cheese, buns and and a games show in which a host dressed as Temporal Lobe Epilepsy shouts “Amygdala has won this round, so she’s going to hit the button and we’re in for a not fun time of sweaty palms and hyperventilation!”

(3) what I really mean here is a common ancestor that we have with modern rats, not an actual modern rat. However, this little critter was probably more rat-like than human-like so I’m going to say rat.

(4) The US law enforcement, court systems and juries are not known for their rigorous standards of proof when it comes to “black man rapes white woman” cases. It’s also harder to remember or recognise the face of someone belonging to a different race. It isn’t just white people who have this problem – it’s a universal human problem.

(5) It’s also another reason why pulling an all-nighter before an exam is a REALLY stupid idea. Learn the things, and then GO TO SLEEP and let the hippocampus organise them.

One thought on “The limbic system and how to prevent it from making you join ISIS: Part 1

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s