Pocket Science – a psychopath's reward, and the mystery of the shark-bitten fossil poo

By Ed Yong | March 15, 2010 8:30 am

Not Exactly Pocket Science is a set of shorter write-ups on new stories with links to more detailed takes by the world’s best journalists and bloggers. It is meant to complement the usual fare of detailed pieces that are typical for this blog.

The rewarding side of being a psychopath

Nucleus_accumbens_psychopat.jpgWhat goes on in the brains of psychopaths? They can seem outwardly normal and even charming, but tthese people typically show a lack of empathy, immoral behaviour and an impulsive streak. Joshua Buckholtz found that the last of these traits – impulsivity – may stem from a hyperactive reward system in the brain and unusually high levels of the signalling chemical dopamine.

When given small doses of amphetamines, people who come out as more impulsive on tests of psychopathy also released more dopamine in a part of their brain called the nucleus accumbens. This region plays many roles in feelings of reward, pleasure and addiction. This link between it and the impulsive side of psychopathy remained even after adjusting for other personality traits. Even the prospect of winning money, as opposed to a physical drug, triggered a hyperactive response from the nucleus accumbens.

When a psychopath imagines a future reward, the explosion of dopamine in their brain provides them with incredible motivation to get that reward. This extra motivation could underlie the increased drug use and the impulsive streaks that accompany the condition. It could even explain some of the antisocial behaviour – dopamine’s most familiar as a chemical linked to feelings of reward and pleasure but studies in mice suggest that its presence in the nucleus accumbens is vital for aggression.

Previous research in this area has focused on the emotionally cold side of psychopathy, which may stem from problems in other parts of the brain like the amygdala, involved in emotions, and the ventromedial prefrontal cortex (vmPFC), involved in fear and risk. The impulsive side of the disorder has typically been overlooked but it predicts many of the problems associated with psychopathy, including drug abuse and violent criminal behaviour.

Reference: Nature Neuroscience http://dx.doi.org/10.1038/nn.2510

Image by Gregory R.Samanez-Larkin and Joshua W. Buckholtz

Why did the shark bite the poo?

Coprolite.jpgThe specimen on the right is a most unusual one. It’s a coprolite, a piece of fossilised dung. That’s not unique in itself; such specimens are often found and they tell us a lot about what extinct animals ate. But this one has a line of grooves running down its middle. They were made by a shark.

Stephen Godfrey and Joshua Smith found two such specimens in Maryland’s Chesapeake Bay. The identity of the coprolites’ maker is a mystery, but its chemical composition suggests that they were excreted by a meat-eating vertebrate. The identity of the biter is clearer. The duo poured liquid rubber into the grooves to make a model cast of the teeth that made them. These model teeth made it clear that the biter was a shark and the duo even managed to narrow its identity down to one of two species -a tiger shark, or Physogaleus, a close extinct relative.

Why would a shark bite a piece of dung? Tiger sharks are notorious for their ability to eat just about anything, but obviously, neither piece of dung was actually swallowed. No known shark eats poo for a living. The shark may have had an exploratory bite and didn’t like what they tasted. But Godfrey and Smith’s favourite explanation is that the bites were the result of collateral damage – the shark attacked an animal and during its assault, it happened to bite through the bowels. These specimens are the enduring remains of a battle between two predators, as suggested by this wonderful drawing in the paper by T Schierer of the Calvert Marine Museum.

Shark-vs-crocodile.jpg

Reference: Godfrey, S., & Smith, J. (2010). Shark-bitten vertebrate coprolites from the Miocene of Maryland Naturwissenschaften DOI: 10.1007/s00114-010-0659-x

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Comments (4)

  1. human

    some thoughts from a young student without any substantial biology/english communcation/psychology experience:
    the more I think about psychopaths/sociopaths the more it seems they act evolutionarily ideally – in the sense of living efficiently and survival based. Their lack of empathy can also be described as intensely logic/rational based actions, where their emotions don’t get in the way of accomplishing tasks. Does this not remind you of how animals act? So what’s the difference between humans and animals?
    I think we can all agree that most humans are not very smart, but can we agree that all (not assuming random exceptions) humans are capable of the same thing? Maybe we are all capable of being psychopaths depending on how much logic was introduced to us at an early age (or maybe the opposite: a completely irrational, illogical, hypocritical influence could cause a human to develop the so called psychopathic tendency).
    Maybe it’s not that psychopaths don’t have “feelings” or “human emotions.” Maybe we are trying to explain something in a language that implies too specific emotional details, which the psychopaths themselves learn so it makes it almost impossible for them to communicate on a level of mutual understanding with biased researchers.

  2. jane

    If anything, the opposite is true – all lines of evidence, from behavior to brain structure and function, indicate that animals have the same emotions we do and engage in plenty of emotion-driven behavior. (Which is good – emotions often encourage us to behave in ways that ensure our survival or that of our descendants.) By contrast, compared to humans, most animals are not very good at abstract, or “logic/rational” thinking.

  3. Hope

    It depends on the animal. A shark, for example, will survive and reproduce by focusing only on itself, but more social animals like honeybees need to cooperate in order to survive and produce offspring. We’re primates – kinda social. If we had all behaved like psychopaths we would never have evolved into humans (maybe something else, but not us). Psychopaths might do well in our society as individuals, mostly because they can rely on the rest of to behave a certain way (want to show trust, be helpful, expect the same), but if we all started behaving that way today, I doubt we would survive much longer. Our niche requires cooperation.

  4. Briana

    Why did the shark bite the poo?
    To get to the other serloin.

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