Striatal dopamine synthesis capacity reflects smartphone social activity

Ubiquitous smartphones and intensive use of social media have prompted speculation about how smartphone use patterns relate to reward processing mechanisms. Here, we leverage day-to-day logs of natural, unconstrained smartphone behavior and establish a link between the intensity of smartphone social activity, and striatal dopamine synthesis capacity using [18F]-DOPA PET in (N=22) healthy adult humans. Specifically, we find that a higher proportion of social app interactions correlates with lower dopamine synthesis capacity in the bi-lateral putamen. Permutation tests and penalized regressions provide evidence that this link between dopamine synthesis capacity and social versus non-social smartphone taps is specific. These observations provide a key empirical grounding for current speculations about dopamine's role in digital social behavior and highlight the potential of naturalistic smartphone behavior as an index of neuromodulatory function.