The lives of sociable spiders

Some spiders are pretty social:

But about 25 arachnid species have swapped the hermit’s hair shirt for a more sociable and cooperative strategy, in which dozens or hundreds of spiders pool their powers to exploit resources that would elude a solo player…In laboratory experiments, the researchers showed that spiders exposed to the same group day after day developed stronger and more distinctive personalities than those that were shifted from one set of spiders to the next. Moreover, the spiders in a stable social setting grew ever less like one another over time.

In other words, far from fostering behavioral conformity, a predictable social life accentuated each spider’s quirks and personal style, rather as the characters in a sitcom — the Goth girl, the huckster, the lovable buffoon — rise ever more to type with every passing laugh-tracked week.

Equally dramatic was the impact of social conditions on the boldness test. Stable spider groups, composed of six spiders that remained together for up to four weeks, showed the greatest variety between individuals, the greatest mix of bold and shy, as well as the highest individual consistency: The pebble-playing times of the boldies grew shorter while those of the timids lengthened. Among shifting spider groups, by contrast, the boldness scores proved far less predictable, as though the spiders didn’t quite know what was expected of them.

I’ve covered some social aspects of spiders before, though have a more complicated social life. The idea that personality evolves through reinforcing already-existing traits has also been explored a little before.

Economic incentives and social behavior

When studying decision-making in neuroscience, experimenters like to have participants be rewarded with money – or units of juice or ‘points’ or suchlike.  Although this may seem like a natural way to measure decisions, we have to step back and ask ourselves whether using this as a basis for reward will affects decision-making in anyway.  Looking around, I found a recent review paper by Bowles and Polania-Reyes that examined how explicit economic incentives change motivation.  Even though it is meant for economists, it has good things to think about for everyone interested in decision-making, motivation, and interpersonal behavior.

Their motivation for this review is clearly set up by a great anecdote.  Before early 2001, Boston firemen were given unlimited paid sick days, trusting them not to abuse it.  In 2001 this policy was replaced with a 15-sick day limit, with penalties for those who went over.  What happened?  Firemen were ten times as likely to call in sick on Christmas and New Years Day, and the total number of sick days claimed more than doubled.  What had been a social privilege instead became an economic transaction.

Rewards are unlikely to be represented in the brain in a purely one-dimensional manner; not everything can be converted equivalently to ‘money’ in some way.  To wit:

Economists know that money is the perfect gift – it replaces the giver’s less well-informed choice of a present by the recipient’s own choice. But when the holidays come around few economists give money to their friends, family and colleagues. This is because we also know that money cannot convey thoughtfulness, concern, whimsy, or any of the other messages that non-monetary gifts sometimes express. A gift, we know, is more than a transfer of resources; it is a signal about the giver and her relationship to the recipient, and money changes the signal.

How we feel about money, reward, and trust is also socially contingent; Bowles and Polania-Reyes report two experiments in societies in Africa, Asia, and Latin America which showed that individuals from more market-integrated societies gave more in the Ultimatum Game.  But it’s not just that they are socially contingent; each offer of resources also sends a social message beyond the purely monetary one.  A low offer can indicate lack of trust, a lack of respect, or a wide range of other things.  The point is that monetary rewards will always have a social effect.  Since monetary offers are in essence social in nature, offers of money for behavior can have side effects on morality; being asked by society to perform an act for money may cause an individual to act more immoral because society has sent the message that morality is unimportant.  And the same offer of money for a behavior can have totally different social meanings depending on the culture:

The fact that fines often work more as messages than as incentives poses a problem for the sophisticated planner because the same intervention may bear radically different messages in different cultures. Bohnet and her co authors implemented a Trust Game in which in one treatment the investor had the option of reducing the payoffs of trustees who betrayed their trust (Bohnet, Herrmann, Al-Ississ, et al. (2010)). Compared to the treatment in which this socalled “revenge” option was not available, when they had the revenge option a substantially larger fraction of Saudi investors trusted their partner, while a substantially smaller fraction of American investors trusted. Making trust more incentive compatible thus had diametrically opposed effects in the two cultures.

Economists like to use revealed preference as a measure of desire or utility.  However, money is not just a reward to individuals, it also contains information and will have side effects on behavior.  This review paper is meant to guide policy makers on how to best provide incentives, with the point that the perceived intent of the incentive is just as important as the incentive itself.  For neuroscience, the point we should take is that we have a lot more to think about when we try to understand decision-making in all its messy glory.

Reference
Samuel Bowles, & Sandra Polania-Reyes (2011). Economic incentives and social preferences: substitutes or complements?  Journal of Economic Literature DOI: 10.1257/jel.50.2.368

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Testosterone: cooperation or competition?

In my last post, I gave an introduction into a couple aspects of testosterone: how it rises and falls, and how it affects decision-making.  I forgot to mention that, neurally, it appears to act substantially through three areas of the brain: the nucleus accumbens, amygdala, and orbitofrontal cortex (OFC).  The nucleus accumbens is a major dopaminergic center, the molecule generally seen as responsible for decision-making and action selection.  Amygdala, as we all know, mediates fear and emotional responses (generally…).  The more interesting area is OFC, which is typically thought to be an area that is involved in self-control.  I couldn’t find many papers that I really wanted to talk about on this aspect of testosterone, so I’ll wait for another day to delve into it.

So let’s look at how testosterone affects social behavior.  In what must have been the Most Fun Study To Participate In Ever, Oxford et al. asked subjects to play Unreal Tournament in teams.  When men are playing the game against other teams, the players that contribute the most show increases in testosterone.  However, when men are forced to play against their own teammates, they have decreased testosterone!  And the subjects who contributed the most to a win showed the largest change.

But if testosterone is increasing during competition against other groups, what affect might it have on social behavior?  Eisenegger et al. used the ultimatum game, where a pair of subjects are given a small amount of money.  One of the subjects then makes an offer of part of the money to the other subject, who can either accept the money or reject it; when the second subject rejects it, neither subject gets any money.  It is well-known that people will generally reject unfair offers.  Following the framework of past studies, female subjects were given either testosterone or placebo and asked to play the game.  They found that subjects who were given testosterone made larger offers than placebo subjects.  Although the authors try to make the claim that this is because being turned down is a ‘status concern’, it could just be because they think that they will make more money that way?  Maybe this is risk-aversion?  I should also note that different study found that subjects given testosterone and asked to be the second subject will also reject more unfair offers.  But the most interesting part about the study is that the subjects who thought that they had received testosterone made much smaller offers – presumably because they already thought they knew what testosterone should do, even though they were wrong!

In a response, van Honk et al. tried using a different game.  He used the ‘public good game’ which is where all players receive 3 moneys, and can contribute some to the public good.  When at least two players contribute to the public good, all players receive 6 moneys.  Note that in this version of the game, with the contribution rate of other players, the expected value is highest when you contribute to the public good.  And subject who have testosterone administered to them give more often to the public good!  So it’s not clear whether they are being more pro-social or just smarter…

The interesting thing about this paper, though is that they also measured the ratio of ring to index finger.  This is a measure of prenatal testosterone exposure, although it doesn’t predict adult levels of testosterone.  Those with a high 2D:4D ratio (ie, those with low maternal testosterone, figure left) are most likely to contribute to the common good, and the less prenatal testosterone, the more of an effect the testosterone given to subjects has.  van Honk et al. suggest that prenatal exposure may change something physically to make subjects more receptive to testosterone, whether it is metabolism or receptor level.  They had found a similar result in a previous study which showed that suspicious individuals didn’t become any more suspicious from testosterone, but the most trusting individuals became much more suspicious when given testosterone (figure right).

The data is a bit hard to interpret, but the general feeling now is that testosterone can act as either a pro-social hormone, or one that makes you more concerned about your social status (egocentrism?).  Although I’d love to give a good clean explanation here, I cannot come up with – and have not yet found – a good unifying framework that unites all the social effects of testosterone .

References

Eisenegger, C., Naef, M., Snozzi, R., Heinrichs, M., & Fehr, E. (2010). Prejudice and truth about the effect of testosterone on human bargaining behaviour Nature, 463 (7279), 356-359 DOI: 10.1038/nature08711

van Honk, J., Montoya, E., Bos, P., van Vugt, M., & Terburg, D. (2012). New evidence on testosterone and cooperation Nature, 485 (7399) DOI: 10.1038/nature11136

Oxford, J., Ponzi, D., & Geary, D. (2010). Hormonal responses differ when playing violent video games against an ingroup and outgroup Evolution and Human Behavior, 31 (3), 201-209 DOI: 10.1016/j.evolhumbehav.2009.07.002

How social status affects your brain

When you get into work in the morning, you might say hi to your coworkers and complain for awhile about your boss.  Then maybe you joke with the janitor, only to flee when you see your boss headed to your desk.  Each of these interactions – as is every interaction between individuals -is deeply embedded in the context of social status.  Social status isn’t just a construct of our world, but a state of our environment that causes profound changes in the way your brain functions.

One way social status affects the brain is through serotonin; it is well known in the scientific literature that changes in serotonin level seems to directly affect perceived social status.  Whether high social status depends on high or low serotonin depends on the species; dominant individuals of species who must fight to retain social status have high serotonin levels, whereas dominant individuals of more cooperative species such as bonobos have low serotonin levels.

Issa et al. looked at social status in crayfish.  Crayfish actually form long-lasting and complex dominance hierarchies where subordinate animals give way to dominants in contests over resources.  Issa et al. took socially isolated animals and let them interact for thirty minutes a day, even though dominance was usually established within the first fifteen minutes.  They then examined the response to these individuals to a surprise touch to the back leg.  Dominant individuals always immediately turned toward the tap, presumably because they were prepared to be aggressive toward some threat.  Submissive individuals, on the other hand, always showed one of two behaviors: they either pushed backwards and then lowered their posture, or they flexed their abdomen, dropped their posture, and then moved backward.  When they recorded from a (specific) neuron that releases serotonin, they found the same kind of stereotyped response from the dominant individuals’ neurons, and the same kind of symmetric response from the subordinates’.  The authors also have a nice model suggesting that the neural circuit itself might be reconfiguring itself by modifying thresholds for firing of excitatory and inhibitory neurons.  It’s a simple result that looks true, though in the field of circuit neuroscience, the easy answer is almost never the right one…

This means that the dominant and subordinate individuals not only have different levels of serotonin, but that their neural circuitry is fundamentally different.  The authors interpret this to mean that a change in status indicates a persistent change is enacted, perhaps by modifying the amount or type of receptors.  The fact that dominance is usually established within fifteen minutes leads one to think that perhaps there is some other underlying difference; however, isolated individuals that weren’t exposed to this dominant-subordinate training acted in roughly the same manner as dominant individuals, with similar neural responses.

For the crayfish, there is probably a trade-off: dominant individuals get more resources, but must also be prepared to fight, perhaps making them more likely to be consumed by predators.  The lessons for humans is probably more complex.  Serotonin is not just linked to social status, but also depression, so it would not be surprising if low social status can literally make us ill.

Reference

Issa, F., Drummond, J., Cattaert, D., & Edwards, D. (2012). Neural Circuit Reconfiguration by Social Status Journal of Neuroscience, 32 (16), 5638-5645 DOI: 10.1523/JNEUROSCI.5668-11.2012

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Why you’ll become an alcoholic unless you get more sex

One very social behavior involves a man and a woman who love each other very much (hint: I’m talking about sex).  Flies who love each other very much obviously also mate, although you may not know that they undergo a courtship ritual first – not just any ol’ fly is getting to home plate.  That’s a behavior I’ll talk more about in a future post.  What I want to talk about here is instead what happens to that unlucky guy who, know matter how hard he tries, isn’t getting any.

A recent paper looked at this very question by taking a bunch of flies, and either having one group that either had a lot of sex or were rejected.  And can I say how awesome this sounds?  Listen to the protocol: one group of male flies experienced 1-hour sessions of sexual rejection three times a day for four days.  Another group experienced six-hour sessions of mating with multiple receptive virgin females for four days.  Let’s just say that you probably couldn’t do this kind of science in people.

The flies were then given the choice between food with alcohol and food without alcohol.  When the flies were sexually satisfied, they went without the alcohol; the flies were rejected needed that extra beer.  It turns out even virgin flies choose the alcohol – though they like it less than the rejected flies – which means that it is the lack of sex that mainly influences how much they need to drink.  If these same flies are allowed to mate?  Then they don’t need the alcohol anymore!

Desire, motivation and addiction in the brain are normally associated with the neural chemical dopamine.  But in this paper they looked at a neural peptide instead.  In humans, the neural peptide Y regulates alcohol consumption, as does all kinds of stress like PTSD and early maternal separation.  The equivalent peptide in fly is neural peptide F (NPF).  When they measured the amount of NPF in these flies, they found that it matched the desire for alcohol: the sexually rejected males had the lowest amount of NPF, the virgins had a little more, and the mated males had the most.  By decreasing the amount of NPF with siRNA or artificially activating it, they were able to control how much the flies wanted the alcohol.

So what is happening in the brain in response to sex?  Sex releases this neuropeptide – NPF in flies, NPY in humans – and the peptide is rewarding!  You love it (no surprise there)!  The peptide probably sets in motion changes in the larger reward system, modifying dopamine transmission over the course of many days.  This reveals the importance of investigating how we interact with our environment and fellow creatures in order to understand how our brain really works.

Reference

Shohat-Ophir, Kaun, Azanchi, Huberlein.  Sexual deprivation increases ethanol intake in Drosophila.  Science (335) 1351-1355.  DOI: 10.1126/science.1215932

See also the perspective.