Prosocial behaviors are behaviors that advantage others and include helping, cooperating, volunteering, comforting, and sharing. The bird pictured below sharing his catch with his friend or mate is an example of a prosocial behavior.

In humans, prosocial behaviors tend to be directed more toward people we like than those we do not like. In the picture below, one could imagine that these birds are not friends and it may be unlikely that the bird gripping the other bird’s beak would share a tasty morsel with the other.

Prosocial behaviors, such as sharing butterflies or other foods, strengthen relationships whereas selfish behaviors weaken relationships. How exactly do liking and disliking people impact prosocial behavior? And how is brain activity linked to making decisions about actions toward people we like and do not like?

These are the main questions asked by Elisabeth Schreuders, Eduard Klapwijk, Geert-Jan Will, and Berna Güroğlu in the award winning article published in the Psychonomic Society’s journal Cognitive, Affective, & Behavioral Neuroscience. To answer these questions, the researchers gathered information about their undergraduate participants’ peers. Participants reported who were the classmates they liked, did not know well, felt neutral toward, or disliked. The researchers then used the natural tendency to share things with people we like but not with people we dislike in a dictator game while each participant was in a fMRI scanner.

The main predictions were:

1. more prosocial behaviors would be directed at friends than other peers, and
2. specific brain regions (shown to be active during interactions with friends) would be active differentially for prosocial and selfish decisions-making toward friends vs. disliked peers.

Here are the specifics:

Undergraduate students rated their classmates and named their classmates who they considered to be friends and their classmates who they least liked. From these responses, the researchers knew the names of the liked, disliked, unfamiliar, and neutral peers of 27 students recruited for the experiment.

While in the scanner, participants took part in different dictator games where they would distribute virtual coins to peers. In the dictator game, there are two players: the first player, known as “the proposer,” determines an allocation of some endowment (typically an amount of money) between themselves and the other player, known as the “responder.” The responder is entirely passive and simply receives whatever portion of the endowment the proposer is willing to give away. Accordingly, participants in the study by Schreuders and colleagues had the options of either giving the coins away or splitting them equally, which are the prosocial options, or keeping the coins or splitting them unequally (keeping more), which are the selfish options.

The figure below shows what participants saw on each trial:

The left panel shows the three names of the participant’s liked, neutral, familiar, or disliked peers (referred to as “others” in the next panels) and one of whom was to be given coins (or not). The participant is in red and the others in blue. The middle panel shows the two options (a prosocial or selfish option) from which the participant chose. The right panel shows the choice made (the option with the red box around it). So, if you were the participant on this trial, you dislike Rick, Wendy, and Sasha and you only gave them one coin when you could have given them two coins.

As predicted, and as shown in the figure below, more prosocial choices were made toward friends (the liked peers) than the other groups (the disliked, neutral or unfamiliar peers), and fewest prosocial were made toward disliked peers than the other groups.

For prosocial choices (i.e., giving more coins), there was greater associated activity for friends compared to disliked peers in the temporoparietal junction (TPJ) and the inferior temporal lobule (pTPJ-IPL) and left putamen (see the figure below). These are regions that previous research has linked with perspective-taking.

For selfish choices (i.e., keeping more coins), there was greater activity in the left superior temporal sulcus (STS)/middle temporal gyrus (see the figure below). These are regions that have been linked with social cognition in previous research.

Holding the choice constant – prosocial or selfish, there were differences in activity in these regions when deciding the coin distribution for a liked versus a disliked peer.

Breaking this down further, Schreuders and colleagues found that fewer prosocial choices to liked peers were associated with greater supplemental motor area (SMA) and anterior insula activity (see the figure below). The SMA and the insula has been linked to a variety of cognitions, including error detection.

Overall these results are in line with the researchers’ two main predictions. First, more prosocial behaviors were directed at friends than other peers, especially disliked peers.

Second, specific brain regions were differentially activated during prosocial and selfish choices, and during choices made to friends versus disliked peers. When selfish choices were made toward disliked peers, there was greater STS activation. Schreuders and colleagues proposed,

“the STS is involved in mentalizing processes, which might be important for recognizing the type of social setting or dynamic in social settings.”

When selfish choices were made toward friends, regions were activated that also respond when social norms are violated (i.e., SMA and anterior insula). Schreuders and colleagues proposed,

“a possible mechanism that could be underlying the neural response in our participants is that they evaluate their behavior based on their norms when interacting with friends…”

This study was the first to investigate these questions using participants’ real peers, which increases the ecological validity compared to previous studies of this kind. Thus, these findings provide another step toward understanding the roles that different brain regions play in social cognition, and how it is influenced by real relationships.

In the future, or in an upcoming Black Mirror episode, one could imagine targeting these specific areas to stimulate an increase in prosocial or selfish behaviors. Probably the most important endeavor, if you wish to create a utopian future, will be to increase prosocial choices to disliked peers. If you wish to create a dystopian future, however, stimulation could be aimed at other areas.

Psychonomics article focused on in this post:

Schreuders, E., Klapwijk, E. T., Will, G-J., & Güroğlu, B. (2018). Friend versus foe: Neural correlates of prosocial decisions for liked and disliked peers. Cognitive, Affective, & Behavioral Neuroscience, 18, 127-142. DOI:  10.3758/s13415-017-0557-1.