Reconciling the Findings
Have we found, then, the brain center for jurisprudence? Probably not: the brain regions identified in this new study, in particular right DLPFC, have previously been highlighted in a number of other studies addressing related but slightly different questions. Unifying patterns do exist, however. We therefore first describe some related studies, and then outline a possible reconciliation between the different findings.
What does rDLPFC do when it isn’t busy assigning responsibility for crimes? One answer comes from a study by Alan Sanfey and colleagues in 2003: these authors found activation in rDLPFC when subjects decided whether to accept or reject a low offer in a two-person economic game called Ultimatum Game. In addition, Daria Knoch and her colleagues in 2006 found that when rDLPFC was deactivated with a technique called repetitive transcranial magnetic stimulation (TMS), participants became less able to reject low offers in this game, although they still judged these offers as very unfair. A different line of work by Joshua Greene and colleagues in 2004 suggests that rDLPFC may be involved in moral reasoning. They presented participants with moral dilemmas such as the decision whether or not to kill one’s own crying child to keep it raising the attention of enemy soldiers and thereby endangering the whole group. The rDLPFC region was activated when subjects acted in the interest of greater overall welfare, against their emotional impulses. Finally, rDLPFC was also highlighted by another study involving social decision-making by Manfred Spitzer and colleagues in 2007: these authors asked participants how much of their wealth they wanted to share with another player. This amount wasn’t very much, usually—unless participants were threatened with punishment. Under the punishment threat, participants transferred more money, and rDLPFC was more active. Moreover, the more subjects changed their behavior under the punishment threat relative to the situation without a threat, the more rDLPFC was activated, suggesting that rDLPFC played a key role in adapting behavior when facing the sanctioning threat.
The Big Picture
How does the new study fit together with the previous ones, and to what extent is a unifying interpretation of the role of rDLPFC across all these studies possible? The findings described above are all consistent with a role for rDLPFC in inhibiting what psychologists call “prepotent responses,” such as knee-jerk reactions. Rejecting a low Ultimatum Game offer means losing money and thus requires overriding the impulse to accept the money. Making utilitarian rather than emotion-driven moral decisions, and resisting the impulse to make low transfers to one’s partner require the suppression of the impulses to save one’s baby, in the one case, and to keep the money, in the other. The activation of rDLPFC in these studies is consistent with the view that rDLPFC is involved in overriding such responses. In addition, the TMS study mentioned above even suggests a key causal role of rDLPFC for overriding prepotent impulses because when rTMS inhibits the recruitment of rDLPFC, subjects are less able to resist the temptation to accept positive, yet unfair, money offers.
Is the new study by Buckholtz and colleagues consistent with this view of the role of rDLPFC? The crucial new element of this study is the fact that participants were instructed to determine “appropriate” judgments of punishment from a third-person perspective. Thus, participants acted like criminal judges; the fact that their punishment decisions correlated strongly with the prison sentences they deemed appropriate for the crimes in question attests to the fact that they saw themselves in this role. Inasmuch as judges are expected to act impartially and objectively, this task, too, requires the suppression of prepotent responses to the crimes described, to produce “just” and impartial punishments. Reading stories about severe crimes may well cause arousing emotional responses that may be associated with a strong desire to punish. Indeed, Buckholtz and colleagues report that activation in the amygdala correlates with punishment judgments, consistent with the role of this brain region in the representation of arousing emotional events. However, the demands of impartiality often require overriding these impulses to produce a reasonable judgment. The higher activation of rDLPFC in the condition where John is responsible for his crime, and when participants decide if and how much to punish him, is therefore consistent with a role for rDLPFC in the suppression of prepotent emotional reactions.