Altruism is a perplexing human trait. It is a form of behavior wherein one individual assists another without an expectation of reward and sometimes even in the face of causing oneself harm. Altruism might be considered one of those traits that distinguishes human beings from animals as it appears to be almost unique to the species. In the animal kingdom, such selfless behavior is limited to the assistance of family members and behavior that may appear altruistic in some pack animals is usually performed for the purpose of benefiting both parties.

Within the realm of game theory, trust games are a useful method of studying altruism and reciprocity in human beings. When employed in conjunction with neuroimaging these games can provide some insight as to the causes behind this kind of behavior. The Dictator Game, for instance, is a game where one of the players has to divide a sum of money as he chooses between himself and a partner. The second player is a passive recipient of the first’s generosity and is required to accept whatever division is proposed. An individual who offers his partner any proportion of the sum would thus be regarded as altruistic and the amount offered would act as a measure of the magnitude of his altruism. This game stems from the more complex Ultimatum Game wherein the two players are in a similar situation, but in this case the second has the option of accepting or rejecting the offer made by the first. If the offer is accepted, the money is divided as decreed. If the offer is rejected both parties receive nothing.

If we were to believe that humans behave the way they do to serve their own self-interest then we would expect the first player to not offer any money in the Dictator Game, and for the second player to accept any offer in the Ultimatum Game. However, this is not always the case and more often than not, human beings seem to be willing to take the risk of placing their trust in another, presumably for the purpose of establishing and maintaining a long term mutually beneficial relationship. Thus the player who provides his partner with a part of the sum of money in the Dictator Game might be doing so with the innate expectation of reciprocation.

The part of the brain that tends to be associated with the performance of this kind of trusting behavior is the ventromedial prefrontal cortex (VMPFC). A study by Krajbich and his colleagues showed how individuals with damage to this part of the brain tend to display less trusting behaviors than a control group. Krabjich’s study together with a more qualitative analysis by Koenigs and Tranel are both consistent in demonstrating how the VMPFC might also be responsible for the affect of guilt where patients with VMPFC damage displayed lower levels of guilt and empathy.

It is interesting to observe how such physiological observations tie in with cognitively-oriented explanations for behavior. One of these explanations theorizes that reciprocal altruism in human beings might be the consequence of a tendency to avoid feelings of guilt. People might engage in altruistic behavior not only because they expect reciprocity on the part of the other person but also because they seek to minimize the guilt that they predict they will experience if they do not. This ties in neatly with a theory of the VMPFC as altruism’s home base. Not only are VMPFC patients likely to be less trusting, less empathetic and less prone to feelings of guilt, but a fully functioning VMPFC operates under a reward mechanism which causes it to light up when performing an altruistic act. Moll and colleagues, in an experiment that compared VMPFC activity in the case of making a charitable donation to activity when the subject was the recipient of a monetary award, found that this part of the brain was noticeably more active when the subject was the giver rather than the recipient of the reward.

Taking psychological and physiological findings together it is not difficult to conclude that altruism, reciprocity and an inclination towards justice and fairness appear to be traits unique to human beings. Cooperative behavior has been observed in some primates but these species, like people, have a larger prefrontal cortex relative to their physical size. Furthermore, such behaviors do not appear in these species quite to the extent that they can be observed in people. These observations, made by Rilling and Sanfey in the Annual Review of Psychology, hold important implications for social psychology. The use of neuroimaging methods (functional MRI in the case above) to discern the physiological bases of behavior not only assists in understanding and verifying cognitive theories of social decision making but also allows for more effective research into the treatment of social disorders.

References:

Koenigs, M., & Tranel, D. (2007). Irrational Economic Decision-Making after Ventromedial Prefrontal Damage: Evidence from the Ultimatum Game Journal of Neuroscience, 27 (4), 951-956 DOI: 10.1523/JNEUROSCI.4606-06.2007

Krajbich, I., Adolphs, R., Tranel, D., Denburg, N., & Camerer, C. (2009). Economic Games Quantify Diminished Sense of Guilt in Patients with Damage to the Prefrontal Cortex Journal of Neuroscience, 29 (7), 2188-2192 DOI: 10.1523/JNEUROSCI.5086-08.2009

Moll J, Krueger F, Zahn R, Pardini M, de Oliveira-Souza R, & Grafman J (2006). Human fronto-mesolimbic networks guide decisions about charitable donation. Proceedings of the National Academy of Sciences of the United States of America, 103 (42), 15623-8 PMID: 17030808

Rilling JK, & Sanfey AG (2011). The neuroscience of social decision-making. Annual review of psychology, 62, 23-48 PMID: 20822437