The zombie brain

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Sunday 17 April 2016 5:05PM

Hopefully you haven’t heard of the psychiatric disorder CDHD—because it describes the brain of a zombie. Symptoms include endless wandering, a lumbering gait, insatiable hunger, anti-social behaviour, and a lack of memory. For All In The Mind, neuroscientists and zombie movie nerds unite in the quest for a better understanding of neuroscience—via the zombie brain.

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Lynne Malcolm: Hi, it's All in the Mind on RN, I'm Lynne Malcolm, and things are about to get a little weird.

[Music: Harry Belafonte]

Yes, it's Harry Belafonte meets Night of the Living Dead. And coming up, a psychiatric disorder you may not be aware of, CDHD. It describes the brain of a zombie.

Zombies are best characterised as the 'living dead', but that's far too simplistic according to self-confessed zombie movie nerds Tim Verstynen and Brad Voytek. They both happen to be respected neuroscientists, and in their recent book Do Zombies Dream of Undead Sheep? they diagnose the brain of a zombie to illustrate some key principles of neuroscience.

Tim Verstynen joins me today. He describes his zombie fixation as pretty pathological. He's an assistant professor in the department of psychology at the Centre for the Neural Basis of Cognition at Carnegie Mellon University in the United States.

Tim Verstynen: The definition of a zombie is quite controversial, and, just as a point of clarification, neither Brad nor myself actually believe zombies really exist, not yet at least…

Lynne Malcolm: It's good to get that straight.

Tim Verstynen: Yes, it's good to get that straight. Actually I should qualify that, that we don't believe they exist for humans, there's actually evidence of zombieism in the insect world, but we can get back to that a little bit later. So in academia there actually is an existing zombie that people publish papers on, and that's the philosopher zombie. And this is often used in a discussion about what is the unique nature of consciousness. And so we are not talking about the philosopher zombie. What we talk about when we refer to zombies are the general genre of the living dead, although in modern movie culture zombies don't necessarily have to be dead anymore, so they've changed to just being essentially a human who's lost all rational free will.

Lynne Malcolm: Before we hear the gory details of how to diagnose the fictional zombie's brain, Tim Verstynen explains that the practise of making a zombie appears as part of the many sacred and secret rituals of the Voodoo religion in The Caribbean. It's now officially outlawed but it was practised in Haiti.

Tim Verstynen: Zombies as a phenomenon exist in the Haitian Voodoo culture. In some ways it's a normative, socially approved form of slavery. What usually happens is an individual who is problematic for a village will be drugged and taken to another side of the island and forced to work as a slave, and part of the ritual of drugging them is thought to use the neurotoxin tetrodotoxin, which is found in puffer fish. And what tetrodotoxin does is it blocks the sodium channels in neurons in the body. So sodium channels are what neurons need to fire to make spikes. And tetrodotoxin works in the body, so what happens is that if you get poisoned with it your muscles stopped contracting, and you basically look like you are dead. If you take a lethal dose, what happens is your diaphragm stops working, so you stop breathing and you will actually die. But if you get a sub-lethal dose, all your movement ceases, you cease reacting, you get locked in in your body and people will think you're dead.

And so in the Haitian zombie ritual it's thought that the individual who is the target of the ritual will be poisoned with tetrodotoxin, people will believe that they are dead and then they will be buried quickly because Haiti is a hot humid culture which means that decomposition happens quickly. So what happens is these people are essentially buried alive. And then when the poison wears off the individual who had given the individual the poison will come to the graveyard and dig up the body and take them away. It's actually a fairly gruesome ritual from our social perspective.

In some ways it carries a lot of the same general ideas of the modern horror movie zombie. You know, an individual is dead and then resurrected. They have no control over themselves. In this sense they have no control over themselves because they are really sold into slavery. But another aspect, we like to say that the Haitian zombie phenomenon is completely independent from the type of zombies that we talk about in the book because these are actually real people who go through fairly traumatic things and we don't want to make light of that, but it has some interesting similarities, both to the phenomenon of modern horror movie zombies and neuroscience because the principal mechanism of action for the ritual is tetrodotoxin which is a neurotoxin.

Lynne Malcolm: Tim Verstynen uses the brain of the fictional zombie character in movies as a way of explaining modern neuroscientific principles.

He and his colleague Brad Voytek in their 'inescapable science nerdiness' have come up with a psychiatric diagnosis of the zombie brain, it's called CDHD.

Tim Verstynen: We refer to zombieism in the book as consciousness deficit hyperactivity disorder, or CDHD for short. And so basically what that means is that these are individuals who have lost conscious awareness and tend to have hypo-activity or slow movement, slow activity. So there's a variety of symptoms, and some of them are not always consistent but, hey, this is science. So one of the most prominent symptoms of CDHD that we talk about in the book is impulse control and aggression. So we talk about the neural circuits that regulate your ability to control your actions and it regulates the fight or flight response.

Another characteristic symptom of zombies in horror movies is that they are not exactly verbally fluent. You can't have a real conversation with a zombie unless you watched Warm Bodies, in which case we will let that slide. But in general they have difficulty understanding what you're saying and they have difficulty communicating. So one of the most famous zombies in zombie movie culture is this man called Tarman, he was a zombie that came out of a tar barrel and he's from the Return of the Living Dead movies, and all he says is, 'Brains!'

In neuroscience we would say that he has aphasia, so he has difficulty communicating, so he is just saying the word that comes straight out of his mouth or straight to his mouth, which is 'brains'. He gets the point across, you know what he's trying to say, but he's not actually saying something like, 'I would like to eat your brain.' So we say language deficits are part of the problem.

We also characterise motor deficits, we talk about how zombies in almost in all classic zombie movies, they are slow, they are stiff-legged, they have this wide stance. Brad and I came up with this hypothesis that the way that they moved had a very specific link to a part of the brain known as the cerebellum. We talked about the link between the cerebellum and movement and how it resembles what you see in zombie movies.

And it turns out we had the chance to talk to George Romero and ask him why he actually made zombies move the way he did. Those of your listeners who don't know who George Romero is he is the director of Night of the Living Dead, so he came up with the modern horror movie genre. And when we asked George Romero why he made zombies move the way he did he said, 'Well, I thought they'd be dead so they'd be stiff.' So our theory kind of went out the window. But nonetheless we talk about it in the book.

Lynne Malcolm: Just mentioning the cerebellum, you say the cerebellum is your favourite part of the brain. Why is that?

Tim Verstynen: It is. It's kind of the unappreciated little brain. The cerebellum sits on the back of your head, really right at the base of your neck. It's this little bulbar structure that looks kind of like cauliflower. And while it's small in size it actually contains almost half the neurons in the entire brain. So it is a very complex, densely connected little brain, and it's actually one of the earliest evolutionary forms of a brain. And it does all sorts of things. It's linked to movement, it's linked to speech, it's linked to all forms of sensory perception. And classically we think about it as being a motor region. Actually I take that back, before we thought it was a motor region, the phrenologists in 19th-century France thought that the cerebellum was the root of the libido, and that was quickly proven wrong. And we started noticing that animals who had damage to the cerebellum had difficulty moving, so it was classically just thought of as a motor control structure. But over the last 20 or 30 years we've discovered that it does all sorts of things and is critical for all sorts of functions, including higher level cognition. So the cerebellum is my favourite area of the brain because it's kind of the underdog of the brain.

Lynne Malcolm: Tim Verstynen. It's All in the Mind on RN, and today we explore the brain of a zombie. For purely neuroscientific purposes of course! Another symptom of CDHD, the zombie brain, is an inability to recognise faces.

Tim Verstynen: So this one is sort of controversial. I had the opportunity to talk about this to some face perception researchers, and some of them actually went back and watched zombie movies and they said, well, we're not sure that you are right. But our hypothesis of zombies and faces is that they suffer damage to an area of the brain known as the fusiform face area, and this is an area that is on the bottom of the neocortex, it's towards the back of the head. And what the fusiform face area is is an area that selectively responds to faces. So when you see a face you get a lot of activity in this area, compared to when you, say, see something like a car or a scene of the Grand Canyon.

And we really quickly with the rise of MRI got a chance to really probe what this area does and its special organisation, and we also started to notice that people who suffered from face blindness tended to have damage or impairments in this specific area. So we were able to make a causal link between thefusiform face area and the perception of faces. And so what happens is with damage to the fusiform face area, is that people see faces, the eyes are in the right place, the nose appears in the right place, the mouth is where it should be, but the ability to identify who owns that face is impaired.

So one of the classic clinical examples of this was a man, he was a German man who had damage to his fusiform face area after falling downstairs, and he had a severe impairment to the point where he saw an image of his face in the mirror, and he had a long beard, and he thought it was a dog. He really couldn't tell who was looking back in the mirror. And he couldn't recognise anybody, his wife who he had known for years, he couldn't recognise famous individuals, and there were lots of other ways that he could hide this disability because he would use cues like how people would dress or the sound of their voice or the way they would walk. But when asked to just identify the face he couldn't.

So when you look in horror movie zombies, this lack of recognition of identity is a very common symptom. So for example as soon as somebody comes back as a revenant in these movies, people that they knew for years, they no longer show that spark of recognition. They go from being your high school sweetheart to just prey to be eaten. And so we say that that change in behaviour gives us a clue that something has gone wrong with the fusiform face area.

Lynne Malcolm: So I wonder if you could describe perhaps your favourite scene from a zombie movie and describe how those symptoms are showing in that movie.

Tim Verstynen: So you're asking a zombie nerd to select a favourite scene from a zombie movie. How long is this interview? I'll pick one…

Lynne Malcolm: Night of the Living Dead is one of the best known ones, but I don't know whether that helps.

Tim Verstynen: I am a purist for Night of the Living Dead, but one of the most fun zombie movies that I think is out there is Shaun of the Dead, it's a British zombie movie and it's all about this goofball and his best friend who somehow manage to battle it out in the zombie apocalypse of London. And there's a scene where Shaun and his friends are trying to get to the safety of a pub, because, you know, they're British.

[Excerpt from Shaun of the Dead]

Tim Verstynen: So halfway between where they are and where the pub is is this giant horde of zombies, and they are all zombies that are basically their neighbours converted into zombies, and they are all looming outside the pub because when you are the walking dead you go back to places that you like to go to when you were alive. And so Shaun and his friends have to figure out a way to get to the pub.

And they cover themselves in viscera and they act like zombies, so they hold their hands out, they make this moan and they just behave in all ways like a zombie. And they are able to meander through this zombie horde and not be attacked because the zombies think they are one of them. So there's this in-group/out-group kind of distinction that gets missed when they start making sounds, walking in a specific away, smelling in a specific way.

And for Brad and I, I think the very first time we saw Shaun of the Dead we immediately thought that this was face blindness, that the zombies weren't recognising that this was Shaun and he's still alive, they just saw another zombie because they were using clues about the movement rather than the look of the face to tell humans versus non-humans. So for a fun and funny example of a zombie movie that shows symptoms that we talk about in the book, that's probably one of my favourite scenes.

Lynne Malcolm: So zombie movies, they are the epitome of a horror movie, but they are also very funny. What is the essence of the horror and the essence of the comedy?

Tim Verstynen: So zombies are a very pliable horror movie monster. Zombies can change and that be still accepted in the genre. So, for example, Night of the Living Dead zombies and all the zombie movies of the '70s and '80s, they were slow-moving creatures, and then suddenly it was okay for them to be fast-moving creatures. And zombies sometimes would be living and sometimes would be dead. So there was no firm structure to the zombie archetype. So that made them pliable not just in terms of being monsters but what you could do with them. So there were actually a lot of underappreciated comedy zombie movies in the '80s, including Return of the Living Dead, which had that Tarman character I mentioned earlier. And they are funny, they are really just silly funny. For the funny part, I think it's just that the contrast of something so horrible yet allowing for silly moments to happen makes that contrast…just allows I guess for the comedy to pop.

The fearful part, I think all the scary zombie movies have this common feature of isolation. Most of the most intense zombie scenes are when the main character is trapped in a room, having to walk through these hallways with these undead creatures out there. And they really play on this idea of being a stranger in a hostile world that gets this very primal sense of fear that we all have. And so I think zombie movies are very successful at that. So I think that's really what makes zombies both funny and fearful. And that was actually one of the things that made it advantageous for Brad and I to use zombies as an educational tool because if you can use a zombie to scare people or to make people laugh, why not use it as an education tool too.

Lynne Malcolm: Coming back to the cause of zombieism, you say that the brain has been hijacked, are there examples in nature where the brain is hijacked like this?

Tim Verstynen: Oh yes, and if anybody wants to sleep at night they should probably stop listening to this part. But there are examples in both the insect kingdom and in humans of brains being hijacked by parasites. So the most well-known form of zombieism occurs in the insect kingdom through a fungus known as cordyceps. So the cordyceps fungus, what it does is it needs to spread its spores in an optimal manner around target insects. So take for example an ant. What will happen is that if an ant gets a spore from a cordyceps fungus, over time its behaviour will start to be a little erratic and a little strange, and it will take riskier moves. So it will go to high places and leave itself exposed, which a normal ant wouldn't want to do because that increases its chances of being eaten by another animal. But these infected ants will go above the colony, find a really nice high spot above the colony, pinch down with their pinchers and then die. And what will happen is a stalk will erupt from their head and spores will be released over the hive again. And what happened is that the fungus hijacked its system to make the ant want to go to that high place and bite down and stick itself on that plant. So it's not like that's a normal action for an ant, the fungus made it do it.

Cordyceps infects other types of insects as well. There are examples of certain wasps that will take control of other insects. So there is the jewel wasp, what it will do is it will inject a stinger into the primitive version of the brain in a cockroach and use a fancy cocktail of neurochemicals to gain control of the cockroach's brain and hijacked the cockroach, so walk it basically into its nest, and then while still alive the wasp will lay its eggs in the cockroach. And the living cockroach will stay there, as happy as can be while these wasp eggs erupt outside of it and eat it. So it's almost something that's perfectly out of a zombie movie.

But lest you think that humans are safe from these kinds of brain hijacking, there is emerging evidence to suggest that some humans can have their brains hijacked by a little monocellular organism known as Toxoplasma gondii. This is a little single-celled organism that often exists in cat poop. So this is actually the parasite that doctors warn pregnant women about. So this is why when you are pregnant you are not supposed to change the litter box. And what normally happens is if you get an infection with Toxoplasma gondii you get flulike symptoms and eventually you get over it. But what happens is that this little organism can only sexually reproduce in the intestinal lining of felines. So what it does is it hijacks the brain of its host to basically take increased risks so that hopefully it will get back into the gut of a feline. We don't have that many large feline predators for humans, but what happens if you have a rodent who is infected with toxoplasmosis, over time the rodent will lose its instinctual fear of felines. So what will happen is it will start to spend more and more time close to cats in the hope that eventually that cat will eat the rodent and then the Toxoplasma in its system will get back into the cat.

Humans, what we see if you get infected with Toxoplasma gondii is that you increase your risky behaviours. So people are more likely to take unnecessary risks. There are the changes in behaviour as well; increased aggression, emotional insensitivity, and these are very small. I'm not saying that this is turning people into zombies, but it is very clear that the changes in behaviour are linked to this organism in their body. So we can even have brain hijacking from parasites.

Lynne Malcolm: So what about the flesh eating aspect of zombies? How is that behaviour explained in neuroscientific terms?

Tim Verstynen: So we actually don't address the specific desire to eat human flesh, but we talk about the neural mechanisms of hunger. And it turns out that there is a really tight link between our guts and our brains, and there are two particular chemicals that regulate feeling hungry and feeling satiated. And we talk about in the book how certain disorders that block one or the other have catastrophic impacts on eating behaviour. So you block the neurochemical that causes this sense of satiation, that you are satisfied with what you ate, you get this hyper eating. People will just keep drinking water, keep eating food. They get these syndromes where they are just constantly ravenously hungry. And so given the fact that zombies are just constantly ravenous and hungry, we suspected that that's what we were seeing, we were seeing this inability to get the chemical signal from the gut to the brain to say that they are full. And so it just so happens that they are so hungry they will eat anything, including the raw human flesh right in front of them.

Lynne Malcolm: So your book is really a big trick, isn't it, it's a trick to engage people in neuroscience.

Tim Verstynen: Yes.

Lynne Malcolm: But I wondered are you also making a tongue-in-cheek comment on psychiatric diagnosis and labelling?

Tim Verstynen: Oh yes, yes we are making fun of everything that we can in this book. So we like to say that we are trying to use the book to trick people into learning basic neuroscience. So we love neuroscience, more people love zombies than love neuroscience, so can we get people's inherent interest in zombies to guide them into thinking about neuroscience problems, and along the way learn a little bit. But also our field has its own idiosyncrasies. So even the term CDHD, we made that as a tongue-in-cheek reference to the fact that everything in neurology turns into an acronym, so why not turn zombies into an acronym too.

And we also have other examples in the book where we talk about how people make mistakes when inferring data from neuroimaging results. We always hear these news stories about the latest brain imaging results shows that this brain area activates when you're in love. Well, that's not exactly what happens. And so we use some tongue-in-cheek references in the book to show how people make those fallacies. These fallacies are not made by just every non-scientist person as well, they are actually made by scientists who work with this data day in and day out. So yes, we like to poke fun at both our field as well as ourselves in the book.

We actually got a chance to meet George at one point as a result of the society, and that's where I checked off about six bucket-list life items at that moment because I have a whole bunch of questionable I've always wanted to ask George Romero, and Brad and I had that opportunity and it was fantastic.

Lynne Malcolm: Does he like the idea that you are using it as a way of teaching about neuroscience?

Tim Verstynen: He thought it was an interesting idea, but take, for example, I had mentioned this a little bit earlier, we were on a panel where we were discussing the difference between fast and slow zombies. And Brad and I came up with this hypothesis that zombies are slow because of damage to the cerebellum, because individuals with damage to the cerebellum have the same kind of movement characteristics as zombies. So we talked about our hypothesis and George looked over and goes, you know, 'I just told my actors, 'You're dead, you're stiff, walk like you're stiff.'' And so it very quickly deflated our theory, and it was like, oh yeah, that would make a lot of sense. So I think he thought it was cute and enjoyed it, and by being part of the Zombie Research Society, obviously he does like the idea that academics are getting into zombies as well.

Lynne Malcolm: So what's the next frontier of zombie neuroscience?

Tim Verstynen: I think Brad and I have fulfilled our obligations of characterising zombies, so that way when the apocalypse happens you are all informed. But we want to keep doing this outreach through popular culture in some way. But I think the zombie problem we have probably solved.

Lynne Malcolm: Well done!

Tim Verstynen, an assistant professor in the department of psychology and at the Centre for the Neural Basis of Cognition at Carnegie Mellon University in the United States.

He's author with Brad Voytek of Do Zombies Dream of Undead Sheep?: A neuroscientific view of the zombie brain.

Find more details on the All in the Mind webpage, where you can also leave comments. Navigate your way there via the ABC RN home page.

Thanks to producer Diane Dean and sound engineer Andrei Shabunov.

I'm Lynne Malcolm, bye till next time.


Tim Verstynen
Assistant Professor,
Department of Psychology,
Carnegie Mellon University


Do zombies dream of undead sheep
Verstynen, T. and Voytek, B.
Princeton Press


Lynne Malcolm
Diane Dean
Sound Engineer
Andrei Shabunov

Comments (3)

Add your comment

  • Jeff :

    16 Apr 2016 12:49:40pm

    The links in red under the videos don't go to YouTube, the just link back to this page.
    Maybe check your links before posting?
    Amusing videos, BTW.

  • Stuart B :

    22 Apr 2016 2:58:27pm

    As someone living with zombism I appreciate the fairness and sensitivity with which you discussed this sensitive subject. Now to shuffle off to the bookstore and buy the book. I expect to devour it in one sitting.

  • Darrell :

    24 Apr 2016 1:02:35pm

    Well.. also from an archetypal psychological point of view James Hillman would want to ask what does "The Zombie" symbolise for us in the modern world.. that is, which to many has become "zombie like" & Soulless.. basically referring to the "death of the poetic imagination" which to the poetic Renaissance mind, referring to the Soul's intimate relationship with "Death".. both literally, & symbolically.. In Hillman's book 'Suicide & the Soul,' he refers to the modern obsession with "facts" & "liberalism" as suicide of the imaginative Soul.. When the heart & the Soul have their home in "the poetic basis of Mind".. Shakespeare etc et al..

    And meanwhile all this with Hillman eternally asking the question, what do our fantasies & "Images" have to say to us about our lives & perhaps about life as a Whole?

    While also taking me back to Hillman's book titled 'Pan & the Nightmare'.. beginning with a chapter on 'The Psyche's Return to Greece'.. asking, us to face our nightmare's to ask the figures or images what they want..

    Psyche’s Return
    to Greece
    Socrates: Beloved Pan & all you other 
    Gods who haunt this place, give me beauty 
    in the inward Soul; & may the outward 
    & inward man-woman be at One. 

    Plato, Phaedrus, 279B

    While also refering to another quote from the start of Melanie Reinhart's book 'Chiron, & the Wounded Healer'.. referring to the lost instinctive or intuitive intelligence beyond the limited walls of the "rational mind"..

    the Roots
    Somewhere beyond the walls
    of our awareness.. the wilderness
    side, the hunter side, the seeking
    side of ourselves is waiting to

    Laurens van der Post