Research press release


Nature Neuroscience

Brain adaptations to dishonesty beget more dishonesty

自分の利益になる不正直な行動を繰り返すと不正直に対する脳の感受性が低下することを報告する論文が、今週のオンライン版に掲載される。今回、管理された実験条件下で不正直の増大を誘導して、測定する研究が行われ、正直からの少しの逸脱が繰り返されるうちに逸脱が雪だるま式に大きくなり、かなりの程度の不正直になってしまう“slippery slope(転落への坂道)”が生物学的に説明されている。

今回、Neil Garrett、Tali Sharotの研究チームが行った実験には80人の成人(18~65歳)が参加し、第1被験者に1ペンス銅貨入りのガラス瓶の画像を見せ、銅貨の数を見積もらせ、その数を第2被験者に伝えさせた。Garrettたちは、 (1)第2被験者が不利益を受けて第1被験者が利益を得る、(2) 第1被験者も第2被験者も利益を得る、(3) 第1被験者が不利益を受けて第2被験者が利益を得る、(4) 第1被験者だけが利益を得て、第2被験者は影響を受けない、(5) 第2被験者だけが利益を得て、第1被験者は影響を受けないというようにガラス瓶の中身に関して不正直になることが誰の利益になるのかという観点から条件を変えながら実験を行った。



Repeated acts of self-serving dishonest behaviour diminish the brain’s sensitivity to dishonesty, reports a paper published online this week in Nature Neuroscience. By eliciting and measuring dishonesty escalation in a controlled laboratory setting, the study provides a biological explanation for a ‘slippery slope’ by which minor deviations from the truth over time can snowball into substantial acts of dishonesty.

Neil Garrett, Tali Sharot and colleagues asked 58 adults (ages 18 to 65) to advise a second person about the amount of money contained in a glass jar of pennies. The authors varied whether dishonesty about the jar’s contents would benefit the participant at the expense of their partner, benefit both parties, benefit the partner at the participant’s expense, benefit only the participant without affecting the partner, or benefit the partner without affecting the participant.

Dishonesty escalated over several trials to a greater degree for the two conditions that benefited the participant (either at the expense of or also benefitting the partner), compared to the condition that benefited the partner at the expense of the participant. Furthermore, the measured level of dishonesty and the degree to which dishonesty escalated were greater when dishonesty benefitted the participant alone, compared to when it benefitted the partner alone, suggesting that these findings were due to self-interest.

A subset of participants completed a version of the experiment while their brain activity was measured by functional magnetic resonance imaging (fMRI). Among these participants, the authors found that the amygdala - a brain region sensitive to emotion-eliciting events - in both brain hemispheres showed a progressively reduced response to self-serving, but not self-harming, dishonesty over time. The reduction in the amygdala’s response to self-serving dishonesty during a given trial could be used to predict the amount that a participant’s self-serving dishonesty escalated in the subsequent trial. None of these findings could be attributed to other brain regions that are also associated with different aspects of deception, which hints at the amygdala’s privileged role in self-serving dishonesty.

doi: 10.1038/nn.4426

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