1 Department of Psychology, Rutgers, The State University of New Jersey, Camden, NJ, 08102, USA. yoona.kang@rutgers.edu.
2 Annenberg School for Communication, University of Pennsylvania, Philadelphia, PA, 19104, USA. yoona.kang@rutgers.edu.
3 Annenberg School for Communication, University of Pennsylvania, Philadelphia, PA, 19104, USA.
4 Department of Psychology, University of Pennsylvania, Philadelphia, PA, 19104, USA.
5 Department of Psychology, Concordia University, Montreal, QC, H4B 1R6, Canada.
6 Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA.
7 Department of Mathematics, Brigham Young University, Provo, UT, 84604, USA.
8 Department of Psychology, Columbia University, New York, NY, 10027, USA.
9 Department of Mathematics, Dartmouth College, Hanover, NH, 03755, USA.
10 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, 19104, USA.
11 Annenberg School for Communication, University of Pennsylvania, Philadelphia, PA, 19104, USA. emily.falk@asc.upenn.edu.
12 Department of Psychology, University of Pennsylvania, Philadelphia, PA, 19104, USA. emily.falk@asc.upenn.edu.
13 Wharton Marketing Department, University of Pennsylvania, Philadelphia, PA, 19104, USA. emily.falk@asc.upenn.edu.
14 Wharton Operations, Information and Decisions Department, University of Pennsylvania, Philadelphia, PA, 19104, USA. emily.falk@asc.upenn.edu.

Evidence on the harms and benefits of social media use is mixed, in part because the effects of social media on well-being depend on a variety of individual difference moderators. Here, we explored potential neural moderators of the link between time spent on social media and subsequent negative affect. We specifically focused on the strength of correlation among brain regions within the frontoparietal system, previously associated with the top-down cognitive control of attention and emotion. Participants (N = 54) underwent a resting state functional magnetic resonance imaging scan. Participants then completed 28 days of ecological momentary assessment and answered questions about social media use and negative affect, twice a day. Participants who spent more than their typical amount of time on social media since the previous time point reported feeling more negative at the present moment. This within-person temporal association between social media use and negative affect was mainly driven by individuals with lower resting state functional connectivity within the frontoparietal system. By contrast, time spent on social media did not predict subsequent affect for individuals with higher frontoparietal functional connectivity. Our results highlight the moderating role of individual functional neural connectivity in the relationship between social media and affect.