R&D Group 4

The brain is a very powerful tool for understanding the mechanisms by which people feels their values and subjectivities. However, it is not easy to clarify the detailed mechanisms that give rise to these subjectivities in the human brain due to the limitation to measure human brain activity. Using macaque monkeys, which are the closest experimental animal to humans, we measure neuronal activity that cannot be measured by non-invasive functional brain imaging in humans, and verify the validity of the neural activity in monkeys and its inter-individual comparison. A technique called decoding is used to reproduce the subjectivity of the individual from the measured neuronal activity, and is compared and examined in comparison with the findings obtained in humans. By actively promoting this interspecies comparison between humans and monkeys, we will build a scientific framework for objectively evaluating the diversity of human subjectivity and find the biologic evidence for evaluating diverse values.

Rewards are anything that satisfies us by obtaining or consuming it. It is not only the basis for adaptive behavior by changing the frequency of its occurrence, but also the core of our happiness by associating with positive emotions such as pleasure. Rewards are not determined solely by the objective characteristics of the external stimulus, but are subjective in that they are highly dependent on the animal's internal state (including humans' value systems). This research project aims to clarify the neural representation of the subjective value of rewards that is processed in a hierarchical manner. To this end, we use macaque monkeys, which are closely related to humans, to simultaneously measure and analyze the activity of many neurons in multiple brain regions, using methods such as devaluation and neural circuit manipulation. The findings from this study will be used to inform other human research projects in our group to compare the neural representations of subjective value and utility of rewards. We will also use our findings to examine the similarities and differences in reward value representations among species by comparing with the rodent study (Group 5).