Manipulating moral judgments… in the lab

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Adding to a growing understanding of the underlying brain functions involved in moral decision-making, a team of researchers at the Massachusetts Institute of Technology and Harvard University—including neuroscientist Marc Hauser, author of the 2006 book Moral Minds— found that manipulating activity in a certain brain region influenced study subjects’ moral judgments. The findings, published this week in the Proceedings of the National Academy of Sciences, suggest that the brain region known as the right temporo-parietal junction (TPJ), located behind the right ear on the surface of the brain, may be critical to moral decision-making.

Previous research has found that there is heightened activity in this particular region when people are evaluating others’ motivation for certain actions—assessing the intentions behind a failed murder attempt, for example. Understanding others’ intentions is a critical part of making moral judgments in what morality researchers refer to as “theory of mind.” (For example, did a man let his girlfriend cross an unstable bridge because he didn’t realize it could collapse, or did he knowingly let her go without a warning?) Inferring the intentions behind people’s actions helps us to make moral determinations, and the TPJ is most active during the process of sizing up people’s motivations.

In this most recent research, investigators found that limiting activity in the right TPJ—by exposing the area to a small magnetic field through a process known as transcranial magnetic stimulation—limited study participants’ ability to determine the intentions behind certain behaviors, and influenced their moral judgments as a result. In two experiments study participants were either exposed to magnetic stimulation for 25 minutes prior to making moral decisions, or for a brief instant just asked a moral dilemma was posed. In both cases, the disruption of activity in the right TPJ resulted in altered moral judgment. In the case of the rickety bridge, for example, normally moral judgments are influenced by whether or not the boyfriend knew the bridge was unsafe before his girlfriend crossed it, not simply whether she managed to get across safely. When activity in the right TPJ was limited, however, participants were far more likely to base moral judgments solely on outcome. That is, failed attempts to harm another person were viewed as morally acceptable—i.e., the boyfriend’s intentions didn’t matter, solely whether his girlfriend made it across safely.

The findings indicate that the right temporo-parietal junction is critical to moral decision-making in so much as it allows us to infer what motivates individual actions, not solely what results from those actions. This study was led by Rebecca Saxe, an assistant professor of brain and cognitive sciences at MIT. A next step in the research, led by study author Liane Young, is to determine how the right TPJ influences moral decision making when outcomes are based on luck, not intention: how moral judgment differs for a drunk driver who makes it home safely, compared with one who gets into an accident and injures someone, for example.