Excessive smartphone use has been repeatedly related to adverse effects on mental health and psychological well‐being in young adults. The continued investigation of the neurobiological mechanism underlying excessive smartphone use—sometimes also referred to as “smartphone addiction”(SPA)—is considered a top priority in system neuroscience research. Despite progress in the past years, cortical morphology associated with SPA is still poorly understood. Here, we used structural magnetic resonance imaging (MRI) at 3 T to investigate two cortical surface markers of distinct neurodevelopmental origin such as the complexity of cortical folding (CCF) and cortical thickness (CTh) in individuals with excessive smartphone use (n = 19) compared to individuals not fulfilling SPA criteria (n‐SPA; n = 22). SPA was assessed using the Smartphone Addiction Inventory (SPAI). CCF and CTh were investigated using the Computational Anatomy Toolbox (CAT12). SPA individuals showed lower CCF in the right superior frontal gyrus as well as in the right caudal (cACC) and rostral anterior cingulate cortex (rACC) compared to n‐SPA individuals (TFCE, uncorrected at p < 0.001). Following a dimensional approach, across the entire sample, CCF of the right cACC was significantly associated with SPAI total score, as well as with distinct SPAI subdimensions, particularly time spent with the device, compulsivity, and sleep interference in all participants (n = 41; p < 0.05, FDR‐corrected). Collectively, these findings suggest that SPA is associated with aberrant structural maturation of regions important for cognitive control and emotional regulation.

<b><i>Background:</i></b> Excessive smartphone use (ESU), that is, a pattern of smartphone use that shows specific features of addictive behavior, has increasingly attracted societal and scientific interest in the past years. On the neurobiological level, ESU has recently been related to structural and functional variation in reward and salience processing networks, as shown by, for example, aberrant patterns of neural activity elicited by specific smartphone cues. <b><i>Objectives:</i></b> Expanding on these findings, using cross-modal correlations of magnetic resonance imaging (MRI)-based measures with nuclear imaging-derived estimates, we aimed at identifying neurochemical pathways that are related to ESU. <b><i>Methods:</i></b> Cross-modal correlations between functional MRI data derived from a cue-reactivity task administered in persons with and without ESU and specific PET/SPECT receptor probability maps. <b><i>Results:</i></b> The endogenous mu-opioid receptor (MOR) system was found to be significantly (FDR-corrected) correlated with fMRI data, and z-transformed correlation coefficients showed an association (albeit nonsignificant after FDR-correction) between MOR and the Smartphone Addiction Inventory “withdrawal” dimension. <b><i>Conclusions:</i></b> We could identify the MOR system as a neurochemical pathway associated with ESU. The MOR system is closely linked to the reward system, which has been recognized as a key player in addictive disorders. Together with its potential link to withdrawal, the MOR system hints toward a biologically highly relevant marker, which should be taken into consideration in the ongoing scientific discussion on technology-related addictive behaviors.

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