Science Questions

Could bacteria affect criminal behaviour?

Tue, 10th Nov 2015

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Paul asked:

I have just read Dr Claire Asher's article about parasites controlling the mind. If swabs were taken at the houses of criminals, I wonder if we would find a pattern of types of bacteria which might inflence the criminal behaviour, either directly or indirectly. I am thinking dust mite droppings, etc.


So, could people say, “Oh, it wasn’t me. It was my bugs.”? Psychologist Ginny Smith took a stab at answering Paul's question... Crime scene

Ginny - That's a really interesting question. So I think the parasite that he's referring to is toxoplasmosis which is a parasite that's very, very common and it lives out its life cycle in rats, but then it has to be passed into a cat to complete its life cycle. So, what it does is it controls that rat's mind and it makes the rat less scared of cats. In fact, it's even attracted to the smell of cat faeces. So, it goes out into the open, it's more likely to be eaten by a cat and that helps the parasite complete its life cycle. Interestingly, lots of humans are carrying this parasite. Most of us, we don't think it causes any harm. Most people don't have symptoms, but it does stick around in our bodies for a long time after we've had it and they found that people who have toxoplasmosis latent inside them are 2.5 times as likely to get into car accidents. So it seems like it might be having some kind of effect similar to the effect it has on rats on us as well. So, could bacteria have the same sort of effect? Well, we're learning more and more about our microbiome, the microbes that live inside us and how much of an effect that can have on all sorts of things. It could affect sleep, mood, memory. It can cause illnesses, it can cause depression, all sorts of things. So, there's a chance that your microbiome could be having an influence on perhaps your risk taking behaviour, perhaps your mood, perhaps making you more aggressive. I haven't found any studies that have been directly looking at that yet. But I did found an interesting one that looked at anti-social behaviour in prisons including violence, and found that by supplementing the diet with vitamins, minerals, and fatty acids, it improved that kind of behaviour. They didn’t really mention how that improvement might have been coming about but we know that your diet has a huge effect on the bugs that live inside you, on your microbiome. So, it's not too big a jump to say that it could've been the microbiome that mediated that effect, but we just don’t know yet.

Chris - Ginny, you beautifully answered Bhavish's question on Twitter because he said @nakedscientists, “How does the food we consume affect our genes but also our gut brain? in other words meaning, the microbiome." So, you've addressed that one. One point about the toxoplasmosis, everything that does carry it carries it for life and the French have some of the highest rates of toxoplasmosis carriage in the world. In fact, up to 80 per cent and that's probably because they subscribed to cooking things at room temperature a lot of the time, but they also have very poor driving record. And so, some scientists have speculated that the poor driving record and therefore, high insurance premiums in France may be directly corelated with toxoplasmosis.

Ginny - The really interesting point from that is what Kat said. Can we say if your microbiome is having that effect? Is it really you that did the crime? But actually, another interesting study is looking at the opposite way around because of course, our microbiomes are signatures. They are as unique to us as our fingerprints. They've recently found that you actually leave that signature behind you. So, they're starting to look at whether you could use microbiomes to solve a crime by looking at who had been in the area.

Chris - And the whole question of, if you have a 'transpoo-sion', are you potentially at risk of acquiring someone's dodgy behaviour because there was an editorial in the British Medical Journal a couple of weeks ago asking that very question? Wasn’t there, Kat?

Kat - Yeah. I interviewed Tim Spector about that. It was really interesting because I think they gave someone who was thin. She had a 'transpoo-sion', a poo transplant from someone who was larger and put on weight. But it's a bit difficult to say if that's really the case. But we won't go down that road. I think we've talked about poo enough on the show and now, I want to hear some news. I want to hear some news this week from Max. what's caught your eye?



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It is known that toxoplasmosis invades the brain and radically affects the behavior of mice (they display suicidal tendencies, like an attraction to cats).

Humans can sometimes be infected by toxoplasmosis from cat feces, and it is known to cause miscarriage in humans.

More controversially, recent research has suggested that toxoplasmosis can invade the human brain, and produce a range of psychological and behavioral symptoms, including an increased risk of car accidents. evan_au, Sun, 27th Sep 2015

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