Social media use is extremely prevalent among adolescents, leading to continued public interest in its effects on social interaction. Understanding the neural underpinnings of social media use will allow researchers to better understand these effects; but the literature on social media and the brain is, at present, remarkably limited. This dissertation examined a unique feature of digital interaction- “Quantifiable Social Endorsement” - and demonstrated that this indicator of peer opinion significantly influences both neural and behavioral responses to content posted online.
In Study 1, adolescents underwent an fMRI scan while using a tool that mimics Instagram, a popular photo-sharing social media platform. Participants viewed photos that had been ostensibly “Liked” by peers. In reality, the number of Likes was experimentally manipulated such that half of the photos appeared with many Likes (‘popular’) and half with few Likes (‘unpopular’). Included among these photos were images submitted by the participants from their own Instagram accounts and images depicting risky behaviors (e.g., drinking alcohol, smoking). Participants demonstrated significantly different behavioral and neural responses as a function of photo popularity. Participants were more likely to Like photographs if they were popular than unpopular, and popular photos elicited significantly greater activity in neural regions implicated in reward processing, social cognition, and visual attention. Behavioral effects were significantly stronger for participants’ own photographs than for photographs ostensibly supplied by peers, and participants showed significantly greater activity in the nucleus accumbens - a hub of the brain’s reward circuitry - for the popular > unpopular contrast when viewing their own photographs compared to others’ photographs.
Study 2 replicated and extended the findings of Study 1 in an expanded sample that additionally included 27 college students. Like the high-school students, college students also were significantly more likely to Like popular than unpopular photographs, and popular photographs elicited significantly greater activity in brain regions involved in social cognition, visual attention, and reward. When high-school students, but not college students, viewed risky (vs. non-risky) photographs, activation in the cognitive control network decreased. For high-school students, nucleus accumbens response to social reward (i.e., receiving many Likes on one’s own photographs) increased with age.
The findings reported in this dissertation suggest that Quantifiable Social Endorsement is a means by which peer socialization and influence occurs in online environments, including to behaviors like drinking and drug use, which represent a significant public health concern in adolescence. Furthermore, social media provide a unique opportunity to examine the neural correlates of social interaction and peer influence in an ecologically valid manner.