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A new study published in the Journal of Neuroscience looked at how the neural representation in the medical prefrontal cortex reveals selfish motivation in white lies.

“In this study, we specifically aimed to identify distinctive neural signatures of selfish and altruistic motivation for Pareto white lies,” study author Dr. Hackjin Kim told us, “particularly focusing on the distinctive functional roles of the subregions in the medial prefrontal cortex in social valuation based on the model recently proposed by our research team.”

Researchers recently proposed a hierarchical allostatic regulation model of the medial prefrontal cortex function for computing values of social decision. According to this model, the medial prefrontal cortex (MPFC) consists of multiple functionally dissociable subregions that are hierarchically organized. For example, the ventral subregion is more sensitive to internal signals from bodily organs (i.e., internal valuation), the dorsal subregion is more sensitive to external signals from the environment (i.e., external valuation), and the rostral subregion, which is located between the ventral and the dorsal ones, is involved in arbitrating between internal and external valuation.

“According to this model, the ventral and the rostral subregions are involved in fast intuitive/internalized social valuation and strategic/context-dependent social valuation, respectively,” Dr. Kim told us. “These subregions can interact with each other to create, maintain, and update values of decision in various situations. Based on this model, we predicted that individuals’ primary motivation behind Pareto lies could be revealed by examining the activity pattern of the MPFC subregions.”

In a former study, researchers found that the rostromedial prefrontal cortex (rmPFC) computes the value of decision for both self and other. In addition, several follow-up studies from the research team demonstrated that the rmPFC is also involved in impression management, conspicuous ethical consumption, and strategic self-protecting behavior, indicating that this region may play key roles in computing context-dependent strategic value computation.

“Based on these findings and the model described above, we hypothesized that the rmPFC may be involved in detecting and resolving the conflict between self-serving and altruistic motivation,” Dr. Kim told us. “We found the Pareto white lie as a perfect candidate for testing this hypothesis because seemingly identical lying behavior can be caused by either selfish or altruistic motivation, which can be revealed only by the neural activity during the lying.”

To test the hypothesis, researchers adopted a brain-fingerprinting approach, which was originally developed to detect concealed information during criminal investigation. In this approach, a target without an explicit label can be classified based on the degree to which the brain response to the target resembles the two known categories. More specifically, contexts in which dishonesty may benefit both self and others may appear as a selfish opportunity to some as they may benefit from dishonesty, whereas the same context may be viewed by others as an altruistic opportunity to benefit others.

“Using the machine learning pattern classification algorithm, we trained the classifier on the mPFC activity pattern for Self and Other beneficiary conditions to distinguish between neural patterns associated with the opportunities to lie for Self and Other,” Dr. Kim told us. “We then estimated individual measures of selfish motivation in Pareto lies by the degree of neural activity pattern in the mPFC for Pareto lies resembles those for selfish versus altruistic lies.”

As predicted, an increase in selfish motivation for Pareto lies was associated with higher mean-level activity in both ventral and rostral mPFC. Additional analyses revealed that the ventral mPFC showed an increased pattern similarity to selfish lies, and the rostral mPFC showed a decreased pattern similarity to altruistic lies.

“These results suggest that, in Pareto white lies, internal motivation for one's own benefit computed by the vmPFC can be reinforced by activating external motivation computed by the rmPFC,” Dr. Kim told us. “Such shared internal motivation for one’s own benefit may have facilitated lying behavior, which was indirectly confirmed by the finding that higher ventral mPFC pattern similarity predicted faster response time in Pareto lies.”

The rmPFC is also engaged in altruistic motivation but with the opposite pattern, possibly indicating that external motivation for Pareto white lies is clearly distinguished from that for altruistic lies.

“Although most of the findings were consistent with our a priori hypotheses, we were surprised by the null finding in neural signatures of altruistic motivation for Pareto white lies,” Dr. Kim told us. “Unlike selfish motivation, altruistic motivation for Pareto white lies may involve different neural processes such as less degree of neural competition in the prefrontal cortex, which deserves further investigation in future studies.”

Dr. Kim believes that identifying the neural mechanisms underlying altruistic and moral behaviors is expected to contribute to a scientific more rigorous understanding of motivations underlying seemingly complex human social behaviors, which can then contribute to designing new policies more suitable for human nature to prevent social conflicts.

“In addition, this research can also be used to develop a more biologically plausible artificial intelligence algorithm,” Dr. Kim told us, “mimicking human moral behaviors as well as more sophisticated lie detection techniques based on state-of-the-art brain imaging techniques.”