In order to create a society that is both free and just, it is essential to evaluate the collective and societal "good" of various public policies. However, it is well known that such indicators cannot be effectively constructed without a way to compare individuals' "happiness" across different people (Arrow's Impossibility Theorem; Arrow, 1963). In recent years, there has been a growing emphasis on life-satisfaction, beyond material wealth as represented by Gross Domestic Product (GDP). In 2022, the United Nations High-Level Advisory Board produced a report on the "Beyond GDP" initiative, in which well-being and agency, as framed in Amartya Sen’s Capability Approach (Sen 1999 Development as Freedom), were identified as key outcome elements.
Our research aims to create innovative technology capable of measuring individuals’ subjective well-being—which has traditionally been difficult to assess objectively—through brain indicators (brain activity), making it possible to compare happiness across individuals. In addition to developing brain indicators related to hedonic happiness, which arises from rewards such as food or money, we will also focus on indicators associated with eudaimonic happiness—derived from the agency (freedom of choice). By aggregating these interpersonally comparable brain indicators of happiness at the societal level, we aim to contribute to the realization of equity based on social choice theory. Through the successful achievement of this project’s goals, brain indicators (brain activity) reflecting individuals’ subjective experiences of happiness can be applied to real-world contexts—such as evaluating mobility policies in smart cities—thereby contributing to the development of social technologies that enhance well-being at the collective and societal levels.

(1) Development of technology to make "happiness" interpersonally comparable through brain indicators (brain activity)

• Using functional magnetic resonance imaging (fMRI) data from a large and diverse sample of several thousand individuals, we demonstrated that subjective "happiness" derived from rewards such as money can be made interpersonally comparable through brain indicators (brain activity). When comparing brain activity related to the desire for money and the pleasure of receiving it across individuals with different socioeconomic statuses (SES), we found that economically disadvantaged individuals exhibited greater brain responses to monetary rewards—indicating higher pleasure—while simultaneously showing lower desire for money. Moreover, we found that brain indicators of subjective "happiness" derived from monetary rewards can be represented as the inner product of a weight vector and a brain activity vector across widespread brain regions, including the prefrontal cortex and basal ganglia. Furthermore, using a behavioral economics model (prospect theory), we confirmed through fMRI that the utility (i.e., subjective value) of monetary rewards can be compared across individuals using brain activity. In addition, magnetoencephalography (MEG) revealed that brain activity patterns—particularly in the frontal lobe and across extensive brain regions—vary depending on utility, with millisecond-scale temporal resolution. These findings suggest the possibility of aggregating individuals’ subjective "happiness" in real time at the societal level using neural indicators. They also challenge a foundational assumption in traditional cost-benefit analysis used in public policy evaluation—namely, that "the value of one yen is equal for everyone." This research paves the way for the societal implementation of policy evaluation systems grounded in brain-based indicators.

(2) Development of technology to measure brain activity related to rich happiness

• Using MEG (magnetoencephalography), we identified the neural dynamics underlying the sense of "choosing and controlling one's own life"—a factor widely recognized as essential to happiness and life satisfaction—through comparative analysis between reinforcement learning models and brain activity. Employing a free-choice task, which represents one of the simplest forms of agency emphasized in the Capability Approach, we found that brain activity was significantly greater during free-choice conditions compared to forced-choice conditions—a phenomenon known as the “free-choice premium.” These findings suggest that it is possible to measure the happiness derived from having opportunities for free choice through brain activity.
• Using single-neuron recordings in humans, we revealed that the ability to form high-level, abstract representations—which enables generalization by leveraging regularities in the world—relies on the abstract and orthogonal encoding by populations of hippocampal neurons (Courellis et al., 2024, Nature). These findings offer important insights into how rich happiness, as experienced in the real world, is represented in the brain.

If we succeed in quantifying the "happiness" of diverse individuals through brain indicators and aggregating it at the societal level, it is expected to become a powerful well-being metric that could complement GDP, as envisioned by the OECD and the United Nations. Going forward, we will conduct neuroscience research under more naturalistic conditions to scientifically identify what constitutes a "rich environment" and "freedom of action"—key elements of happiness in contemporary society. By recreating these enriched environments using technologies such as virtual reality and precisely controlling them, we aim to enhance brain-measurement accuracy through the use of various brain imaging techniques, thereby ensuring scientific validity and rigor in our development efforts.
(MATSUMORI Kaosu: Hitotsubashi University, MATSUMOTO Madoka: Kyoto University, Ralph Adolphs: Caltech)