people and their relationships with each other? The human brain has mechanisms to support the ability to keep track not only of all of the different people in our lives, but also of the complicated relationships between those people. Scientists have begun to look at how the ways that we use our brains are related to features of our social worlds, like the number of friends that we have and whether we play an influential role in our social groups.
How do scientists study the relationships between people's social worlds and the ways that they use their brains? For many years, neuroscientists (that is, scientists who study the brain) have studied people's brains without considering the social environment in which people live. Meanwhile, other scientists-including mathematicians, statisticians, and sociologists-have developed many tools to study networks. There are many different types of networks. Some examples are networks of roads between locations in a city, flights between airports, power lines between houses, and the World Wide Web. However, people are particularly attuned to one specific type of network: our social networks. Most typically, a social network is a
A network in which, typically, each node represents a person and each edge represents some type of connection (such as a friendship) between two people. collection of people who know each other and the relationships between those people [ , ]. Recently, scientists have begun to combine the study of brains with the study of social networks to help us understand how our brains support our ability to socialize and connect with other people.
Scientists can study a social network in many ways. Suppose that a researcher seeks to characterize the social network of students at your school based on friendships. To do this, the researcher can study which students are friends with each other. In network-science terms, the students are called nodes and each friendship between two students We can also use the information in a social network to calculate how close people in the network are to each other. This is an abstract type of distance. Suppose that we pick two random students, Felicity and Marco, in a school's social network. We can calculate the distance between Felicity and Marco using the information about who their friends are. If Felicity and Marco are friends with each other, there is a distance of between them. If they are not friends with each other, but Felicity is friends with Amy who is friends with Marco, then Marco and Felicity are "friends of friends," so there is a distance of between them (see Figure ).
How can we relate the rich information in a social network to how the people in that network use their brains? One way that scientists have begun to study this question is by collecting and examining brain data from people in the same social network. Scientists often collect brain data using a technique called functional magnetic resonance imaging (fMRI). A magnetic resonance imaging (MRI) scanner uses powerful
The set of roles that an individual plays in a social network. These roles can relate to various things, including who their friends are, whether or not they have many friends, or whether or not they "bridge" people who otherwise might not be connected to each other. Scientists often use surveys to collect information about people's social networks. For example, scientists can ask people to list their friends, and they can then use the responses to their questions to characterize those people's social networks. Scientists can also obtain information about how people's brains respond to the world by measuring their brain activity using fMRI. Scientists can then combine the information from brain scans with information about people's social networks to study how our brains and social worlds interact with each other. (Image credit: Flaticon.com) information about other people's social-network positions when we see people who we know (see Figure ) [ ]. Why would our brains automatically do this? One reason may be that keeping track of other people's social-network positions can help us navigate our social worlds. For example, perhaps you only want to share a secret with your closest friends. Additionally, it could be risky to tell a secret to the most popular student at school because this person is connected to a lot of other people.
Scientists have discovered that people in certain social-network positions use their brains differently in specific situations. For example, recent research has revealed that the brains of people with a large degree (that is, popular people) track the degrees of other people especially closely [ ]. In other words, popular people may pay particularly close attention to the popularity of their peers. Scientists have also studied whether or not people with large brokerage use their brains differently. In one study, researchers found that the brains of people with large brokerage were particularly sensitive to determining when other people's opinions were different from theirs [ ]. These people had especially elevated activity in brain areas that are involved in thinking about what other people are thinking about. This is a very important function for people with large brokerage because they provide social bridges to connect groups of people who may have different beliefs or opinions.
Scientists have also compared how the brains of people in the same social network process the world around them. In one study, researchers examined a social network of business-school students [ ]. Some of these students participated in an fMRI investigation in which they watched a bunch of movie clips. Students who were closer together in the social network (for example, students who were friends) had more similar brain activity, and students who were farther apart had less similar brain activity. Friends had especially similar brain activity in brain regions that are involved in processing emotions and interpreting movies. This study suggests that people who are closer to each other in their social network may think in similar ways when they watch movies and perhaps also when they experience other things. When you see a friend, your brain automatically keeps track of their social-network characteristics. For example, Felicity's brain calculates Marco's degree. Because Marco is connected to two people, Marco's degree is . When Felicity sees Marco, her brain calculates the distance between them in their social network. Marco is a friend of a friend of Felicity, so the distance between them is . (Image credit: Adobe Stock File # )
Consider the similarities between you and your friends. Do you and your friends laugh at the same jokes or feel similar emotions when you watch movies? This may reflect similarities in how you and your friends think about the world around you.
Even though scientists have found that people in different social-network positions have brains that operate differently, they
have not yet discovered if differences in the brain lead to people occupying particular social-network positions or if occupying particular social-network positions causes changes in the brain [ ]. This is hard to resolve in humans. For instance, it would be very difficult to randomly assign many friends to one person and no friends to some other person. Even if it were possible to randomly assign people to different social-network positions, it would be unethical to do so. . doi: . /frym. .
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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