Moral and perceptual conflict processing are implemented by distinct brain activation and functional connectivity patterns

Abstract

While humans resemble other primates in terms of motor and perceptual abilities, our behavior is uniquely characterized by morality—the ability to choose our actions based on specific ethical values. The evolutionary origins and neurobiological basis of moral behavior are debated intensely, with opposing proposals about whether moral decisions rely on domain-general decision-making neural circuitry (neural common currency hypothesis) or on unique neural processes that were shaped by evolutionary pressures associated with life in groups (social brain hypothesis). Here we examine the potential overlap between moral and perceptual decision-making, by combining functional magnetic resonance imaging with computational modeling of behavior in a novel task requiring human participants to make alternating moral and perceptual choices on identical stimuli. At the algorithmic level, we found that moral and perceptual choices were well fit by the same sequential sampling model, which allowed us to quantify and directly compare conflicts between the choice alternatives for both types of decision-making. At the implementational level, moral and perceptual choice conflicts were represented by distinct neural activity patterns; in fact, neural signals in some brain areas (e.g., temporoparietal junction) encoded the strength of the two types of conflict in opposite directions. Our findings suggest that while similar computational decision mechanisms underlie both moral and perceptual choices, their neural implementation is fundamentally different, supporting the social brain hypothesis.