The Enforcer

Ugh...

Brain's 'social enforcer' centers identified

Researchers have identified brain structures that process the threat of punishment for violating social norms. They said that their findings suggest a neural basis for treating children, adolescents, and even immature adults differently in the criminal justice system, since the neural circuitry for processing the threat of such punishment is not as developed in younger individuals as it is in adults. The researchers also said that their identification of the brain’s “social norm compliance” structures also opens the way to exploring whether psychopaths have deficiencies in these structures’ circuitry.

Manfred Spitzer, Ernst Fehr, and colleagues published their findings in the October 4, 2007 issue of the journal Neuron, published by Cell Press.

“In this study, we sought to uncover the neural circuits involved in forced norm compliance,” wrote the researchers. “This question touches the very foundations of human sociality because the establishment of large-scale cooperation through social norms is a unique feature of the human species. Norm compliance among humans is either based on people’s voluntary compliance with standards of behavior that are viewed as normatively legitimate or on the enforcement of compliance through punishment. Although much compliance is voluntary, there can be little doubt that social order would quickly break down in the absence of punishment threats because a minority of noncompliers can trigger a process that leads to widespread noncompliance due to the conditional nature of many people’s compliance.

“To our knowledge, this is the first study [NOTE: it feels like the first time] that examines the brain processes involved in humans’ behavioral response to the threat of punishment for social norm violations,” wrote the researchers.

You know, I've been wondering about the brain's "social norm compliance structures" since, oh, September 13, 1848 (the date of Phineas Gage's infamous encounter with a tamping iron that exploded through his head). The accident resulted in bilateral damage to his prefrontal cortex and major changes in his personality. ¹ From Wikipedia:

According to Gage's doctor, Dr. J.M. Harlow, whereas previously he had been hard-working, responsible, and popular with the men in his charge, his personality seemed to have been radically altered after the accident. His doctor reported that:

"Gage was fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating, devising many plans of future operations, which are no sooner arranged than they are abandoned in turn for others appearing more feasible. A child in his intellectual capacity and manifestations, he has the animal passions of a strong man. Previous to his injury, although untrained in the schools, he possessed a well-balanced mind, and was looked upon by those who knew him as a shrewd, smart businessman, very energetic and persistent in executing all his plans of operation. In this regard his mind was radically changed, so decidedly that his friends and acquaintances said he was 'no longer Gage." (Harlow, 1868)

You can read more about the Phineas Gage story here and here (and of course, in Damasio et al., 1994). He even has a fan club.

OK, back to the new and novel study of Spitzer et al. (2007). From the abstract, here is a quick summary of their neuroimaging results:

Individuals’ increase in norm compliance when punishment is possible exhibits a strong positive correlation with activations in the lateral orbitofrontal cortex and right dorsolateral prefrontal cortex. Moreover, lateral orbitofrontal cortex activity is strongly correlated with Machiavellian personality characteristics. These findings indicate a neural network involved in social norm compliance that might constitute an important basis for human sociality.

So what were the social norms, and what was the "forced compliance"?? A gun to the head? A police station right around the corner? No, the social norm was financial fairness, and the threat was financial punishment. Their fMRI study used tasks popular in neuroeconomics (Sanfey et al., 2006): the dictator game (the no punishment condition) and the ultimatum game (the threat of punishment condition). More specifically,

Two players, A (in the scanner) and B, interacted anonymously with each other. Each knew that he was facing a human player. Player A received an endowment of 100 money units (MUs), which he could distribute freely between himself and player B. In the control [no punishment] condition, which resembles a dictator game, B was a passive recipient of A’s monetary transfer. In contrast, B could punish A in the punishment condition after having been informed of the latter’s decision. Each player received an additional endowment of 25 MUs in both conditions, for reasons of fairness and to make punishment possible. In the punishment condition, B could spend all or part of this amount to reduce A’s earnings; every MU B invested into punishment led to a reduction of A’s earnings by 5 MUs. ... Thus, the punishment condition resembles an ultimatum game, with the exception that player B has a larger set of available punishment actions.

Quite a few neuroimaging experiments have scanned subjects during the performance of those types of tasks (reviewed in Sanfey et al., 2006), ² so what's different about the current paper? [besides its wild extrapolations to when the Vandals invaded and looted Rome, when the police went on strike in Liverpool and Montreal, and when ATM robberies in New York increased on September 11, 2001.]

...although important work examining the neural bases of economic choice, social cognition, moral judgment, social cooperation, and social punishment exists [NOTE: 16 references deleted for readability], the brain systems involved in forced norm compliance still remain unknown. In particular, the previous literature on social punishment examines the neural circuitry involved in the decision to punish whereas our work focuses on the neural circuitry involved in the processing and the response to punishment threats that are associated with norm violations.

So, what was predicted, and what were the results?

We therefore conjectured that during the decision phase, lateral prefrontal areas such as the dorsolateral prefrontal cortex (DLPFC), or the ventrolateral prefrontal cortex (VLPFC), which have been shown to be reliably involved in cognitive control and the inhibition of prepotent responses, will be more strongly activated in the punishment condition.
. . .

In the punishment condition player A also has to evaluate the sanctioning threat. Several studies suggest lateral orbitofrontal cortex (OFC) involvement in the evaluation of punishing stimuli that may lead to behavioral changes. These findings
led to the conjecture that the OFC might be more strongly activated in the punishment condition.

Previous transcranial magnetic stimulation (TMS) studies have shown that when the normal functioning of right DLPFC is transiently disrupted, participants accept a higher proportion of unfair offers (van't Wout et al., 2005; Knoch et al., 2006), so in general we know this region is important for decision-making in these types of tasks. In my view, what's most interesting is a brain region that was not activated (and not even mentioned by name in the entire paper): the anterior cingulate cortex, which has been associated with those same cognitive control functions described above. Why? We'll never know. Instead, as predicted, bilateral DLPFC, VLPFC, and OFC showed larger hemodynamic responses in the punishment condition than in the no punishment condition. Additionally, activitions in the right DLPFC and the Machiavellian lateral OFC were positively correlated with social norm compliance [the insula was also Machiavellian]. How were Machiavellian tendencies assessed, you ask? Before scanning, participants completed the Machiavelli questionnaire [not that this might have influenced their behavior in the study, oh no].

Interestingly, a brand new paper in Science (Jensen et al., 2007) demonstrated that chimpanzees (Pan troglodytes) behave rationally (i.e., according to models of rational economic decision making) in the ultimatum game: they do not reject unfair offers to punish the bad player. Unlike humans.

And what about Gage?


from Fig. 5 of Damasio et al. (1994): the white blobs indicate the estimated trajectory of the metal bar. The areas spared by the iron are highlighted in color: Broca, yellow; motor, red; somatosensory, blue; Wernicke, green.

Although he didn't play the ultimatum game (to our knowledge), other ultimatum game players with damage to the ventromedial prefrontal cortex (part of the OFC) are more likely to reject unfair offers than controls (Koenigs & Tranel, 2007). We don't know yet whether they would be more inclined to give skimpy offers despite the threat of punishment (i.e., when in the "player A" position), but one might imagine this would be the case (Fellows, 2007)...


Footnotes

¹ But see this criticism of the popular story.

² See also The Trust Game and Men are Torturers, Women are Nurturers...


References

Damasio H, Grabowski T, Frank R, Galaburda AM, Damasio AR. (1994). The return of Phineas Gage: clues about the brain from the skull of a famous patient. Science 264: 1102-5.

Fellows LK. (2007). Advances in understanding ventromedial prefrontal function: the accountant joins the executive. Neurology 68:991-5

Harlow, JM. (1868). Recovery from a Passage of an Iron Bar through the Head. Publications of the Massachusetts Medical Society 2: 327-347.

Jensen K, Call J, Tomasello M. (2007). Chimpanzees are rational maximizers in an ultimatum game. Science 318:107-9.

Knoch D, Pascual-Leone A, Meyer K, Treyer V, Fehr E. (2006). Diminishing reciprocal fairness by disrupting the right prefrontal cortex. Science 314:829-32.

Koenigs M, Tranel D. (2007). Irrational economic decision-making after ventromedial prefrontal damage: evidence from the Ultimatum Game. J Neurosci. 24:951-6.

Sanfey AG, Loewenstein G, McClure SM, Cohen JD. (2006). Neuroeconomics: cross-currents in research on decision-making. Trends Cog Sci. 10:108-16.

van't Wout M, Kahn RS, Sanfey AG, Aleman A. (2005). Repetitive transcranial magnetic stimulation over the right dorsolateral prefrontal cortex affects strategic decision-making. Neuroreport 16:1849-52.

Spitzer M, Fischbacher U, Herrnberger B, Grön G, Fehr E. (2007). The Neural Signature of Social Norm Compliance. Neuron 56: 185-196.

All known human societies establish social order by punishing violators of social norms. However, little is known about how the brain processes the punishment threat associated with norm violations. We use fMRI to study the neural circuitry behind social norm compliance by comparing a treatment in which norm violations can be punished with a control treatment in which punishment is impossible. Individuals' increase in norm compliance when punishment is possible exhibits a strong positive correlation with activations in the lateral orbitofrontal cortex and right dorsolateral prefrontal cortex. Moreover, lateral orbitofrontal cortex activity is strongly correlated with Machiavellian personality characteristics. These findings indicate a neural network involved in social norm compliance that might constitute an important basis for human sociality. Different activations of this network reveal individual differences in the behavioral response to the punishment threat and might thus provide a deeper understanding of the neurobiological sources of pathologies such as antisocial personality disorder.