Neuro-Gifting

‘Tis the season…for a lot of things. No matter what holiday you celebrate, December tends to be a month to get together with family, give each other gifts, and if you’re still feeling generous, give money to charity. The end of this month also tends to involve the consumption of a great deal of alcohol…stay tuned for a NeuWrite post on that topic next week.

Why do we give gifts? In terms of natural selection, individuals should only perform actions that directly benefit their own chances of survival and reproduction. On the surface, giving away something for free seems like the opposite of advantageous; yet such altruism is incredibly common in human society (for a good review of human altruism see: Fehr & Fischbacher 2003) and is present to a limited degree in some animal species, particularly bonobos (Tan & Hare 2013). The study of why and how humans exhibit altruism involves a healthy blend of social psychology and neuroscience – not to mention evolution. How do we decide who to give gifts to and whether to give them at all?

Giving leads to receiving

There are certainly several self-interest incentives for individuals to give, such as tax exemptions for charitable donations. Alternatively, when you give a gift to someone during the holidays, you generally will also receive a gift from that person – or else you may stop giving them gifts. This situation is a form of direct reciprocity, the idea that by helping or giving to another person, you increase your chances of receiving help from that person in the future (Fehr & Fischbacher 2003). Bonobos, among our closest living primate cousins, readily participate in direct reciprocity: when given the choice to share food with another bonobo or to keep it all to themselves, they almost always share (Tan & Hare 2013). Surprisingly, when they have the choice between sharing with a groupmate and sharing with a stranger, these primates tend to share with the stranger! One theory to explain this behavior is that sharing with strangers is a good way to make new bonobo friends.

These bonobos appear to be friends. Perhaps their friendship began with a food exchange?

A more complex incentive for giving revolves around what other people think of us. Indirect reciprocity is the idea that being observed by others while performing an altruistic act may improve your reputation, making the observers or people that have heard about your generosity more likely to do you a favor or otherwise help you in the future. This has been demonstrated in psychological studies: when participants are split into donor and recipient groups, the donor builds a reputation based on their decisions on whether to give money to the recipients. When these roles switch, participants with better reputations are more likely to receive donations (Fehr & Fischbacher 2003). Furthermore, when people believe they are being observed, they are more likely to perform prosocial behaviors such as donating to charity (Bereczkei et al. 2007).

However, autistic individuals appear to be insensitive to how their actions could affect their social reputation. Izuma et al. (2011) found that the amount of money that high-functioning adults with autism donated to charity (in a lab setting) was not affected by the presence of an observer, in contrast to the control group, which donated more money in the presence of an observer. Importantly, autistic individuals were not simply oblivious to the observer: in the same study, a separate test of social facilitation demonstrated that the presence of an observer improved the performance of both autistic and control groups on a sustained attention task. This study suggests that autism involves a specific neural deficit in the area of the brain that modulates altruism according to its potential impact on reputation.

Because (almost) everyone else is doing it

Direct and indirect reciprocity do not fully explain the extent of human altruism. For that, social psychologists have formulated the idea of strong reciprocity, which involves both rewarding altruistic behavior and punishing behavior that disobeys social norms, even when the cost to the rewarder or punisher is unfair (Fehr et al. 2002). The ultimatum game provides a good example of altruistic punishment. In the game, there are two participants: a proposer and a recipient. The proposer is given a set amount of money, and decides whether and how much to offer to the recipient. The recipient can accept the offer, receiving the money, or reject the offer, in which case neither the proposer nor the recipient gets anything. A recipient wishing to maximize her payout should accept every offer, but in fact most recipients reject offers of 25% or less of the proposer’s money (Fehr & Fischbacher 2003). This demonstrates the tendency of people to punish behavior they perceive to be unfair, even at some cost to themselves.

This guy offered less than 25% of his share.

He offered less than 25% of his share.

A model of human evolution based on strong reciprocity (Gintis 2000) predicts that in situations where humans faced extinction threats, groups with more strong reciprocators – who perform individually costly behaviors that benefit the whole group – were more likely to survive, even when a few group members were purely selfish. In addition, altruistic punishment may be key to maintaining cooperation over long periods of time, since even purely selfish individuals will be discouraged from cheating, ensuring some stable level of cooperation from everyone in the group (Fehr & Fischbacher 2003). This may explain why some individuals punish at extra cost to themselves: during our evolution, the groups with more strong reciprocators survived to reproduce.

In neuroscience terms, there is evidence that the evolution of social reciprocity played a role in shaping our brains (de Quervain 2004). In an economic exchange task, 2 subjects were given 10 money units each, and subject A decided whether to give B money, after which B decided whether to give A money. Following the exchange, A had the option to punish B for being unfair. Using positron emission tomography (PET), de Quervain et al. scanned the brain of subjects in group A while they decided whether and how much to punish B, and found that punishment activated the dorsal striatum, associated with reward centers in the brain. This suggests that the brain evolved to feel good about altruistic punishment, which was likely very important for enforcing social norms in the early evolution of humans and could explain why most criminal justice systems are based on punishment.

This is your brain on generosity

Let’s get back to giving. To date no study has recorded from people’s brains while they experience the joy of giving a gift to a close friend or family member. However, a few have recorded neural activity while subjects decide how much money to give to various charities, a situation that is much easier to reproduce in the lab. In one experiment, Moll et al. (2006) gave participants $128, then put them in an fMRI scanner and asked them to decide whether to donate a portion of their $128 to real charities. At the end of the experiment, each participant took home the amount of money they had left after donating. A person who only cared about their monetary self-interest should donate nothing in order to keep all the money, but of course, many of the subjects donated significant money—an average of 40% of the $128.

Your brain on generosity, probably.

Your brain on generosity, probably.

Brain scans showed that several areas in the mesolimbic reward system (ventral tegmental area, dorsal striatum, and ventral striatum) were activated by decisions leading to both pure monetary reward and charitable donation. However, the subgenual area, involved in social attachment and affiliative reward, was activated significantly more by donation than monetary reward, suggesting that while the rewarding feeling we get from giving may be very similar to the feeling of receiving, there is an important social component to the reward we feel from giving. Other areas were activated by decisions of whether or not to donate: the lateral orbitofrontal cortex was associated with subjects’ decisions against donating, while the anterior prefrontal cortex was activated by donations in which participants were particularly altruistic (i.e. lost a lot of money). Is this an altruism decision circuit in the brain? It’s hard to say for sure, but the fact that specific brain areas are activated in this way suggests that altruism played an important role in human brain evolution.

So is it better to give than receive?

Maybe…the above study suggests that more regions are activated by giving than receiving, but whether one actually feels better than the other is hard to say. Perhaps the more important question in light of evolution is why do we like giving so much? Evidence points to cooperation and altruism being integral to our survival as a species, even if it did not necessarily benefit every altruistic individual. The proclivity of another highly social primate species, bonobos, to share with strangers supports the view that this type of behavior promotes the survival of groups. In addition, the existence of specialized brain areas for processing altruism and their connections to reward centers suggest that these pressures on the survival of groups of humans significantly influenced the evolution of our brains. And while altruism is not uniquely human, the extent to which we cooperate with and give to complete strangers is unmatched in the animal kingdom – even bonobos do not share with strangers if there is no potential for social gain (Tan & Hare 2013). So while you’re enjoying giving gifts to your family and friends this holiday season, consider the reason why it feels good to give: the interaction between cultural evolution and human brain evolution.

References

Bereczkei, T., Birkas, B. & Kerekes, Z. Public charity offer as a proximate factor of evolved reputation-building strategy: an experimental analysis of a real-life situation. Evol. Hum. Behav. 28, 277–284 (2007).

de Quervain, D. J.-F., Fischbacher, U., Treyer, V., Schellhammer, M., Schnyder, U., Buck, A., & Fehr, E. The neural basis of altruistic punishment. Science 305, 1254–8 (2004).

Fehr, E., Fischbacher, U. & Gächter, S. Strong reciprocity, human cooperation, and the enforcement of social norms. Hum. Nat. 13, 1–25 (2002).

Fehr, E. & Fischbacher, U. The nature of human altruism. Nature 425, 785–91 (2003).

Gintis, H. Strong reciprocity and human sociality. J. Theor. Biol. 206, 169–79 (2000).

Izuma, K., Matsumoto, K., Camerer, C. F. & Adolphs, R. Insensitivity to social reputation in autism. (2011).

Moll, J. et al. Human fronto-mesolimbic networks guide decisions about charitable donation. Proc. Natl. Acad. Sci. U. S. A. 103, 15623–8 (2006).

Tan, J. & Hare, B. Bonobos share with strangers. PLoS One 8, e51922 (2013).

Advertisements