-Araya Inc. Neurotechnology R&D Unit Research Team Leader
-National Institute for Physiological Sciences Section of Brain Function Information Associate Professor
The Chikazoe group hopes to actively carry out joint research with companies, universities, etc.
The group is also looking for postdoctoral researchers and interns. Please feel free to reach out using the inquiry form below.
Research Plan Overview
Since economic and moral judgments are evolutionarily new functions of the brain, the neural bases responsible for them are thought to have diverted from brain regions that previously performed other functions. The group conducts a series of fMRI experiments under the hypothesis that the neural basis of affective value judgment has been diverted to economic and moral judgment functions.
Past experiment results in behavioral economics have shown an imbalance in human sensitivity towards gains and losses; that is, individuals tend to be more loss averse. Taking inspiration from these findings, the group particularly focuses on presenting stimuli that simultaneously cause affects of pleasure and displeasure (ambivalent stimuli) in eating, economic, and moral judgment tasks.
By measuring people's brain activity while performing these tasks, the study aims to identify brain regions associated with a stimulus’ pleasure, displeasure, and integrated value information, and reveal the role of affect in economic and moral decision-making. While previous research has focused on discovering representations of economic and ethical concepts within the brain, this study attempts to explain economic and ethical phenomena using the biological idea of homeostasis.
The academic context and core academic question of this study
As Adam Smith notes in The Wealth of Nations, classical economics assumes an economically rational individual, the Homo economicus, who seeks to maximize self-interest or utility. Experiment results in behavioral economics, which combines economics and psychology, have shown instead that an individual’s economic behavior deviates significantly from economic rationality (Ariely, 2008), yet the underlying mechanisms that cause this are unclear. Since monetary economic activity is unique to humans and has emerged very recently in the species' history, the neural basis of economic behavior can be considered as a result of exaptation, in which evolutionarily older systems are diverted to newer, different purposes. This study aims to verify the hypothesis that the occasionally irrational economic judgments of an individual are caused because of the exaptation of neural bases. Furthermore, the study assumes that there is a neural basis that integrates both positive and negative stimuli, in addition to the neural bases that separately process the two. Based on this assumption, it employs fMRI to identify the neural bases of the following affective values: pleasure, displeasure, and integrated value information.
According to prospect theory, the central theory of behavioral economics, individuals perceive the significance of gains and losses differently and tend to be more loss averse. For instance, past experiments have shown that most people avoid entering a gamble that could double $100 if they have $100 of savings but are more enthusiastic in the gamble if they have $100 of debt (Kahneman and Tversky, 1979). Such results suggest that the information processing of gains and losses are performed by separate brain systems, and that they are not integrated in a way that follows economic rationality.
Under the hypothesis that economic decision-making is processed by an affective system linked to homeostasis, this study attempts to explain the irrationality of people’s economic behavior as shown by behavioral economics from evolutionary and psychological perspectives. Regarding food consumption, a process directly related to homeostasis, stimuli such as high-calorie foods and those that help maintain internal homeostasis evoke pleasure, while stimuli that are potentially toxic, such as bitter foods, evoke displeasure (Nissim et al., 2017). A slight taste of bitterness combined with strong sweetness is not perceived the same way as weak sweetness but rather as a mixture of high caloric substances and potential toxicity. The decision-making process of whether to swallow such a food can be complex, considering its nutritional status and the metabolic capacity of its toxic component; however, in practice, it can be reduced to a simple decision between pleasure and displeasure. If such systems have been diverted to economic decision-making, it is understandable that individuals cannot calculate quantitative differences between economic gains and losses, and risk-averse behavior is a rational response unless the individual is in a state of homeostatic danger (e.g., starvation). In order to understand the irrationality of human economic behavior, it is therefore essential to investigate how stimuli containing a mixture of pleasure and displeasure are processed in the brain; yet, few studies have managed to directly address this issue. This study focuses on the brain’s information processing mechanism of pleasure, displeasure, and integrated value of stimuli, and reveals how it conducts the integrative processing of value information in the areas of food consumption, economy, and morality.
This study’s purpose, in addition to its academic originality and creativity
This study employs fMRI to identify the common neural bases for decision-making processes of food consumption, economics, and morality, and examines the role of affect in economic and moral decision-making. This study has the following features:
1) Providing feedback from neuroscience to economics and ethics
Conventional neuroeconomic research has focused on finding representations of economic concepts (e.g., money) in the brain; that is, attempting to introduce economic ideas into neuroscience. This study takes the opposite approach: it employs neuroscientific and biological concepts, namely homeostasis, to explain phenomena in economics and ethics. This approach makes it possible to develop economic systems and ethical norms that are “natural” for human beings.
2) Accumulating knowledge on the multidimensional expression of affective values
By modeling pleasure and displeasure as independent two-dimensional variables rather than the opposing poles of a unidimensional spectrum, Chikazoe et al. experimentally showed that their information is combined in the orbitofrontal cortex (Chikazoe et al., 2014, Nature Neuroscience). With a proven track record in research involving the two-dimensional representation of affective values, the group has the credentials to lead research in this field.
33) Universal values observed in various sensory modalities and abstract dimensions (economics and morality)
When individuals make value-based selections of their own actions, they are presumably able to conduct flexible decision-making because their brain represents value information beyond what is provided by sensory modalities. Based on this perspective, the group is constructing a system to present stimuli with affective value through various sensory modalities (e.g., sight, taste, hearing, and touch), while also searching for brain representations of universal values that do not depend on sensory modalities. This study explores the universality of the brain representations of affective values, starting with taste and expanding into more abstract dimensions of study such as economic and moral values.
Considering this study’s position and role in the research area, what, how, and to what extent it aims to clarify and contribute to the progress of the research area
This study plays a central role in the research area “affective informatics”. Based on the hypothesis that affective values — i.e., pleasant and unpleasant affects — are diverted to economic judgments between gains and losses, the study will uncover the mechanisms behind irrational economic behavior by reconsidering affective values from the perspective of homeostasis. Furthermore, it will show that affective values play a significant role in moral judgment and other functions that have arisen from complex evolutionary processes. Specifically, the study conducts three types of fMRI experiments with collaborator Jimura of Keio University to reveal how positive and negative values (pleasure and displeasure, respectively) are processed by different pathways in the brain and what neural bases are involved in their integration.
[Experiment 1] Investigating the integrated calculation process of ambivalent values in taste
Taste stimuli with ambivalent value can be created by mixing sweet- and bitter-tasting stimuli in various proportions. From the perspective of homeostasis, sweet taste holds a positive value because it contains high calories, while bitter taste indicates toxic components such as plant alkaloids (the experiment will use a non-toxic stimulus, catechin, and subjects will be informed in advance about its safety). This experiment aims to show that the integrated value of stimuli cannot be measured simply by the difference between pleasure and displeasure, as well as identifying the brain regions associated with the three factors of pleasure, displeasure, and integrated value through fMRI. Subjects are given solutions that contain sweet and bitter tastes in various proportions (ratio of sweet to bitter = 100:0, 99:1, 95:5, 90:10, 70:30, 50:50, with concentration also varying between 100%, 30%, and 10%), to which they will decide whether to swallow or not. They are also asked to provide feedback on how pleasant or unpleasant the stimulus was in each trial. Subjects are expected to swallow solutions that do not contain a bitter taste regardless of the solution’s concentration, while refusing to swallow mixed solutions depending on how strong the bitter taste is. The experiment further aims to show that the frequency of subjects swallowing does not correlate with the difference between the stimuli’s pleasure and displeasure, in addition to employing fMRI to identify the brain regions that are associated with pleasure, displeasure, and integrated value (inferred from frequency of swallowing).
[Experiment 2] Investigating how the ambivalence of rewards in gambling is processed
This experiment tests the hypothesis that individuals cannot measure economic gains and losses on the same scale because their information is processed by different brain circuits. The homo economicus makes decisions based solely on the difference between gains and losses. However, as mentioned above, if gains and losses are not measured on a single axis but on two qualitatively different axes, the brain most likely has regions that can perceive the independent magnitudes of gains and losses, in addition to the difference between them, when placed in a situation that involves gains and losses simultaneously.
[Experiment 3] Investigating the role of ambivalent value judgment systems in moral decision-making
This experiment tests the hypothesis that complex moral judgments also depend on affective value judgment systems. A moral dilemma, when considered as a thought experiment, can be redefined as an individual making an ambivalent value judgment when confronted by an ethical issue. The trolley problem is a prime example, asking whether the respondent would save five lives at the expense of one or vice versa. Previous studies on the problem have revealed that respondents’ decisions can change depending on the superficial expressions used to explain the problem, even though they are essentially judging the same situation (Hauser et al., 2007). Although there is an ongoing debate on how evolutionarily old the neural basis for moral judgments is, non-human primates also show a certain sensitivity to fairness which suggests at least a precursory conception of morality (Brosnan, 2013). Therefore, the sense of morality may have originated from an evolutionarily older structure in the brain, which may serve as indirect evidence for the idea that moral judgment processes are diverted from affective valuation systems, similar to how economic judgments originate from the external adaptation of such systems.
The expected result is that decision-making in complex issues such as moral judgments are influenced by, or in extreme cases replaced by, judgments between pleasure and displeasure. This is demonstrated at the neural basis level through fMRI. Furthermore, having considered the role of affect in moral decision-making, the group cooperates with Kodama, an ethics researcher at Kyoto University, to reinterpret utilitarianism as homeostasis within groups and aim to construct a normative theory that resolves the contradictions between affect-based and reason-based judgments (Chikazoe et al., 2014, Nature Neuroscience).
This study extends the aforementioned two-dimensional model to construct a model of affective value that consists of three dimensions: pleasure, displeasure, and integrated information. Many neuroeconomic studies have attempted to find regions in human and Japanese macaque brains that are responsible for representing economic concepts (Padoa-Schioppa and Assad 2006; Rangel 2008). However, there have been no attempts to modify economic or ethical concepts to be suitable for studying the mechanisms of the biological brain. Through intradisciplinary (economics: Watanabe and Kayaba) and interdisciplinary (ethics: Kodama) joint research, this study aims to apply findings from affective research to academic disciplines in the humanities, in addition to providing a starting point for the reconstruction of economics and ethics as fields that integrates affect with reason.
J. Chikazoe, S Konishi, T Asari, K Jimura, *Y. Miyashita, ‘Activation of right inferior frontal gyrus during response inhibition across response modalities’, Journal of cognitive neuroscience 19 (1), 69-80. (2007), IF: 3.029, CI: 280
*J. Chikazoe, K. Jimura, T. Asari, K. Yamashita, H. Morimoto, S. Hirose, Y. Miyashita, and S. Konishi, 'Functional Dissociation in Right Inferior Frontal Cortex During Performance of Go/No-Go Task', Cereb Cortex, 19, 146-52.(2009a) IF: 5.437, CI: 225
*J. Chikazoe, K. Jimura, S. Hirose, K. Yamashita, Y. Miyashita, and S. Konishi, 'Preparation to Inhibit a Response
Complements Response Inhibition During Performance of a Stop-Signal Task', J Neurosci, 29, 15870-7. (2009b) IF:6.074, CI: 267
*J. Chikazoe, 'Localizing Performance of Go/No-Go Tasks to Prefrontal Cortical Subregions', Curr Opin Psychiatry,23, 267-72. (2010) IF: 4.483, CI: 156
*J. Chikazoe, D. H. Lee, N. Kriegeskorte, and *A. K. Anderson, 'Population Coding of Affect across Stimuli, Modalities and Individuals', Nature Neuroscience, 17, 1114-22. (2014) IF:17.194, CI: 137
*J. Chikazoe, D. H. Lee, N. Kriegeskorte, and *A. K. Anderson, ‘Distinct representations of basic taste qualities in human gustatory cortex’, Nature communications, 10 (1), 1048. (2019) IF: 11.878, CI: 3 Jimura K, Locke HS, Braver TS (2010) Prefrontal cortex mediation of cognitive enhancement in rewarding motivational contexts. Proc Natl Acad Sci USA 107:8871-8876.
Tsumura K, Aoki R, Takeda M, Nakahara K, Jimura K (2021) Cross-hemispheric complementary prefrontal mechanisms during task switching under perceptual uncertainty. J Neurosci. (in press) (doi: 10.1523/JNEUROSCI.2096-20.2021)
Tanaka D, Aoki R, Suzuki S, Takeda M, Nakahara K, Jimura K (2020) Self-controlled choice arises from dynamic prefrontal signals that enable future anticipation. J Neurosci 40:9736-9750.
H. Itai, A. Inoue, S. Kodama, 'Rethinking Nudge: Libertarian Paternalism and Classical Utilitarianism', The Tocqueville Review/La Revue Tocqueville 37(1) 81 – 98 (2016)
S. Kodama, 'On Herbert Spencer's Evolutionary Ethics' The Journal of philosophical studies 603 39 - 58 12 (2018)
S. Kodama, "Practice and Ethics: For Thinking about Contemporary Issues", Keiso Books (2020)
S. Kodama, "An Introduction to Utilitarianism: Ethics for Beginners", Chikuma Books (2012)