Humans typically discount future gains more than losses. This phenomenon is referred to as the "sign effect" in experimental and behavioral economics. Although recent studies have reported associations between the sign effect and important social problems, such as obesity and incurring multiple debts, the biological basis for this phenomenon remains poorly understood. Here, we hypothesized that enhanced loss-related neural processing in magnitude and/or delay representation are causes of the sign effect. We examined participants performing intertemporal choice tasks involving future gains or losses and compared the brain activity of those who exhibited the sign effect and those who did not. When predicting future losses, significant differences were apparent between the two participant groups in terms of striatal activity representing delay length and in insular activity representing sensitivity to magnitude. Furthermore, participants with the sign effect exhibited a greater insular response to the magnitude of loss than to that of gain, and also a greater striatal response to the delay of loss than to that of gain. These findings may provide a new biological perspective for the development of novel treatments and preventive measures for social problems associated with the sign effect.

We propose a new avenue for studying income comparisons effects, namely hypothetical discrete choice experiments in which respondents are presented with alternative combinations of hypothetical monthly income amounts, both for themselves and certain reference persons. With this experimental method we can avoid the problems associated with researcher-imposed reference persons' incomes that are found in most of the happiness studies testing comparison effects. This approach * We thank the associate editor and the two anonymous referees for their constructive and detailed advice that has substantially improved the paper. We also appreciate helpful comments from Andrew

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