The Brain Represents Others as a Summation of Their Mental States

Post by Flora Moujaes

What's the science?

To be successful in life it helps to take people’s individual dispositions into account. For example, a good teacher will tailor their teaching strategy to the temperament of the student, encouraging shy students to participant more while challenging the assumptions of overconfident students. However, we still don’t have a clear picture of how people tailor their actions to the idiosyncrasies of specific individuals. Traditionally, it has been assumed that people may do this by representing others using traits: the unchanging characteristics that define someone, such as trustworthiness or intelligence. More recently, it has been suggested that people represent others using summed states: feelings people experience on a moment-to-moment basis, such as happiness or shame. There are three main reasons that representing others using states may be advantageous (1) states are easier to observe than traits, as they can be seen in the moment rather than having to get to know someone over a long period of time, (2) states, even if unrelated to a person’s general disposition, are an independently useful for predicting behaviour, and (3) by summing someone’s mental states over time, one can infer long-term characteristics or traits.

This week in Nature Communications, Thornton and colleagues demonstrate in an fMRI study that we represent other people as the sum of their moment-to-moment states, as our neural representations of other people are composed of combinations of representations of the mental states those people are perceived to frequently experience.

How did they do it?

To explore the hypothesis that the brain represents others according to a sum of their states, the authors began by establishing the pattern of brain activity associated with 60 different celebrities, from Shakespeare to Snoop Dog, based on the states people associated with each celebrity. To do this they first conducted an fMRI experiment to establish what patterns of activity are elicited when the brain thinks about each mental state (e.g. patience). They then conducted an experiment to determine which mental states were associated with each celebrity (e.g. is Snoop Dog patient?). Finally, they combined the data from both studies to come up with a pattern of brain activity for each celebrity based on the set of states associated with them.


They then tested whether the pattern of brain activity they created for each celebrity based on the states associated with them, reflected the brain activity seen when people thought about the celebrities. In order to do this, they conducted an additional fMRI experiment where they asked people questions about each celebrity (e.g., how much would Snoop Dog like to learn karate?) to get them to think about the celebrity. They then correlated the artificial (based on the states associated with them) and actual patterns of brain activity elicited by thinking about these famous people.

What did they find?

Testing the Summed State Account: They found evidence that people did represent others as a sum of their states, as there was a correlation between the artificial patterns of brain activity created for each celebrity based on the states associated with them, and the actual brain activity of each participant when thinking about the celebrity. Summed State vs. Trait Accounts: They also compared whether participants’ neural representations of celebrities were better explained by considering the states or traits associated with a celebrity. They found that the summed states account consistently outperformed the trait alternative in explaining person representation.

For more details see Thornton’s summary on Twitter.

What's the impact?

This is the first study to show that when you think about a person, your brain may represent them as the sum of the mental states you think that they frequently experience. This suggests that people tailor their actions to the unique characteristics of individuals by observing differences in their momentary thoughts and feelings. These findings also help us understand the relationship between how we might think about people's momentary thoughts and feelings to infer their long-term traits. Thus, the trait–state divide may be narrower than commonly thought. Overall, the summed state hypothesis provides a compelling model of how the mind and brain may learn about, represent, and predict other people.


Thornton et al. The brain represents people as the mental states they habitually experience. Nature Communications (2019). Access the original scientific publication here.