How Does the Brain Map Our Increasingly Complex Social World?

Post by Flora Moujaes

What's the science?

When navigating the world around us it is imperative we keep track of our increasingly complex social network: who our family, friends, and co-workers are, and how they relate to each other. Developing a map of our social environment is useful as it allows us to make inferences in novel situations or based on sparse information. We know from previous research that when we encounter a new physical environment, such as a new city, we first sample the environment, building up small and separate representations. Then, as we get to know the physical environment better, we integrate these representations into a coherent internal map. So is the same process used to represent abstract relationships, such as social networks? This week in Neuron, Park and colleagues use fMRI to show that the brain builds maps of social networks the same way it builds maps of physical space.

How did they do it?

To investigate how the human brain constructs maps of social hierarchies, 27 participants were trained on a task where individuals ranked in two social hierarchies: popularity and competence. The training involved the participants being given relational information about the two dimensions, on different days. For example, the participant may be presented with two individuals, Alice and Bob, and informed that Alice is more popular than Bob. The true social hierarchy could thus be mapped as a two dimensional grid defined by the two hierarchies: popularity and competence. 

To explore whether the human brain represents social hierarchies as a one dimensional or multidimensional map, and what brain regions are involved in the representation, the training period was followed by an fMRI experiment. This experiment examined whether participants represent social hierarchies in a single dimension (e.g. they have separate maps for competency and popularity) or in two dimensions (e.g. competency and popularity are represented in the same map). To do this participants were required to make inferences about the relative competency and popularity of novel pairs of individuals. Neural activity was examined in various regions of the brain including the hippocampus and entorhinal cortex, which organize both spatial and non-spatial relational information into a reference map, and the orbitofrontal cortex, which is theorized to represent a goal or the current state in a task structure to guide goal-directed decision making. 

What did they find?

The researchers found that the brain spontaneously represents individuals’ status in social hierarchies in a map-like manner in 2-D space, as participants were able to generalize to both social hierarchies (popularity and competence) when presented with novel pairs. They also found that distances between people in the 2-D grid were related to neural activity, as the pattern similarity between faces represented in the hippocampus, entorhinal cortex, and the medial orbitofrontal cortex was related to the distance between faces in the social network grid.  This result is particularly striking, as the grid itself was never shown to participants, demonstrating that participants instinctively built up this grid-style map of social hierarchy from relational information they received about pairs of participants.

What's the impact?

Overall this study suggests that the brain utilizes the same neural system for representing our physical space and our social network. It shows that by building a social network map, participants are able to make accurate inferences about novel situations. Further, these results support the theory that the hippocampus and entorhinal cortex play a key role in constructing a global map from local experiences, whether physical or social.

Park et al. Map making: Constructing, combining, and inferring on abstract cognitive maps Neuron (2020). Access the original scientific publication here.