New Paper on Oxytocin and Generosity

In Plos One:

• Zak, P. J., Stanton, A. A., & Ahmadi, S. (2007). Oxytocin Increases Generosity in Humans. . PLoS ONE, 2(11), e1128.
  

see this previous post for a presentation of the research.

Oxytocin and Sociality

Oxytocin is really the sociality hormone. It is involved in recognition (Popik et al., 1992) and postcoital bonding (Waldherr & Neumann, 2007). It improves mindreading in autistic (Hollander et al., 2006) and non-autistic humans (Domes et al., 2007b). It increases trust (Kosfeld et al., 2005; Zak et al., 2005) and generosity (Stanton et al., 2007). It was generally thought that its modus operandi is a modulation of amygdala (associated with fear) (Kirsch et al., 2005), but a new paper by (Domes et al., 2007a) suggests that it attenuates amygdala responses tout court.

References

• Domes, G., Heinrichs, M., Glascher, J., Buchel, C., Braus, D. F., & Herpertz, S. C. (2007a). Oxytocin Attenuates Amygdala Responses to Emotional Faces Regardless of Valence. Biological Psychiatry, 62(10), 1187-1190.
• Domes, G., Heinrichs, M., Michel, A., Berger, C., & Herpertz, S. C. (2007b). Oxytocin Improves "Mind-Reading" In Humans. Biological Psychiatry, 61(6), 731-733.
• Hollander, E., Bartz, J., Chaplin, W., Phillips, A., Sumner, J., Soorya, L., Anagnostou, E., & Wasserman, S. (2006). Oxytocin Increases Retention of Social Cognition in Autism. Biol Psychiatry.
• Kirsch, P., Esslinger, C., Chen, Q., Mier, D., Lis, S., Siddhanti, S., Gruppe, H., Mattay, V. S., Gallhofer, B., & Meyer-Lindenberg, A. (2005). Oxytocin Modulates Neural Circuitry for Social Cognition and Fear in Humans. J Neurosci, 25(49), 11489-11493.
• Kosfeld, M., Heinrichs, M., Zak, P. J., Fischbacher, U., & Fehr, E. (2005). Oxytocin Increases Trust in Humans. Nature, 435(7042), 673-676.
• Popik, P., Vetulani, J., & van Ree, J. M. (1992). Low Doses of Oxytocin Facilitate Social Recognition in Rats. Psychopharmacology (Berl), 106(1), 71-74.
• Stanton, A. A., Ahmadi, S., & Zak, P. J. (2007). Oxytocin Increases Generosity. Paper presented at the Economic Science Association 2007 World Meeting.
• Waldherr, M., & Neumann, I. D. (2007). Centrally Released Oxytocin Mediates Mating-Induced Anxiolysis in Male Rats. Proceedings of the National Academy of Sciences, 104(42), 16681-16684.
• Zak, P. J., Kurzban, R., & Matzner, W. T. (2005). Oxytocin Is Associated with Human Trustworthiness. Hormones and Behavior, 48(5), 522-527.

[PNAS] Why Sex is Good, and The Evolutionary Psychology of Animate Perception

in this week PNAS:

A glimpse at the evolutionary psychology of animal perception, by New, Cosmides and Tooby (famous evolutionary psychologists):

Visual attention mechanisms are known to select information to process based on current goals, personal relevance, and lower-level features. Here we present evidence that human visual attention also includes a high-level category-specialized system that monitors animals in an ongoing manner. Exposed to alternations between complex natural scenes and duplicates with a single change (a change-detection paradigm), subjects are substantially faster and more accurate at detecting changes in animals relative to changes in all tested categories of inanimate objects, even vehicles, which they have been trained for years to monitor for sudden life-or-death changes in trajectory. This animate monitoring bias could not be accounted for by differences in lower-level visual characteristics, how interesting the target objects were, experience, or expertise, implicating mechanisms that evolved to direct attention differentially to objects by virtue of their membership in ancestrally important categories, regardless of their current utility.

• New, J., Cosmides, L., & Tooby, J. (2007). Category-specific attention for animals reflects ancestral priorities, not expertise. Proceedings of the National Academy of Sciences, 104(42), 16598-16603.
  

And the reason why sex makes people feeling good: it's all oxytocyn! Waldherr and Neumann showed that "sexual activity and mating with a receptive female reduce the level of anxiety and increase risk-taking behavior in male rats for several hours" (!) because "oxytocin is released within the brain of male rats during mating with a receptive female"

• Waldherr, M., & Neumann, I. D. (2007). Centrally released oxytocin mediates mating-induced anxiolysis in male rats. Proceedings of the National Academy of Sciences, 104(42), 16681-16684.

More than Trust: Oxytocin Increases Generosity

It was known since a couple of years that oxytocin (OT) increases trust (Kosfeld, et al., 2005): in the Trust game, players transfered more money once they inhale OT. Now recent research also suggest that it increases generosity. In a paper presented at the ESA (Economic Science Association, an empirically-oriented economics society) meeting, Stanton, Ahmadi, and Zak, (from the Center for Neuroeconomics studies) showed that Ultimatum players in the OT group offered more money (21% more) than in the placebo group--$4.86 (OT) vs. $4.03 (placebo).
They defined generosity as "an offer that exceeds the average of the MinAccept" (p.9), i.e., the minimum acceptable offer by the "responder" in the Ultimatum. In this case, offers over $2.97 were categorized as generous. Again, OT subjects displayed more generosity: the OT group offered $1.86 (80% more) over the minimum acceptable offer, while placebo subjects offered $1.03.

Interestingly, OT subjects did not turn into pure altruist: they make offers (mean $3.77) in the Dictator game similar to placebo subjects (mean $3.58, no significant difference). Thus the motive is neither direct nor indirect reciprocity (Ultimatum were blinded one-shot so there is no tit-for-tat or reputation involved here). It is not pure altruism, according to Stanton et al., (or "strong reciprocity"--see this post on the distinction between types of reciprocity) because the threat of the MinAccept compels players to make fair offers. They conclude that generosity in enhanced because OT affects empathy. Subjects simulate the perspective of the other player in the Ultimatum, but not in the Dictator. Hence, generosity "runs" on empathy: in empathizing context (Ultimatum) subjects are more generous, but in non-empathizing context they don't--in the dictator, it is not necessary to know the opponent's strategy in order to compute the optimal move, since her actions has no impact on the proposer's behavior. It would be interesting to see if there is a different OT effect in basic vs. reenactive empathy (sensorimotor vs. deliberative empathy; see this post).

Interested readers should also read Neural Substrates of Decision-Making in Economic Games, by one of the author of the study (Stanton): in her PhD Thesis, she desribes many neurpeconomic experiences.

[Anecdote: I once asked people of the ESA why they call their society like that: all presented papers were experimental, so I thought that the name should reflect the empirical nature of the conference. They replied judiscioulsy : "Because we think that it's how economics should be done"...]

References

• Kosfeld, M., Heinrichs, M., Zak, P. J., Fischbacher, U., & Fehr, E. (2005). Oxytocin increases trust in humans. Nature, 435(7042), 673-676.
• Stanton, A. A. (2007): Neural Substrates of Decision-Making in Economic Games. Published in: Journal of Dissertation Issue 1.Volume 1 (2007): pp. 1-63.
• Stanton, A. A., Ahmadi, S., & Zak, P. J. (2007). Oxytocin Increases Generosity. Paper presented at the Economic Science Association 2007 World Meeting.