The brain represents situations and mental states as sums of their action affordances

Human behavior depends on both internal and external factors. Internally, people’s mental states motivate and govern their behavior. Externally, one’s situation constrains which actions are appropriate or possible. To predict others’ behavior, one must understand the influences of mental states and situations on actions. We hypothesized that the brain achieves this goal by representing situations and states in terms of associated actions. To test this, we used functional neuroimaging to estimate neural activity patterns associated with situations, mental states, and actions. We computed sums of the action patterns, weighted by how often each action occurs in each situation and state. We found that these summed action patterns reconstructed the corresponding situation and state patterns. These results suggest that the brain represents situations and mental states as sums of their action affordances. Summed action representations thus offer a biological mechanism by which people can predict actions given internal and external factors.