Supplementary Material for: Neurochemical Correlates of Cue Reactivity in Individuals with Excessive Smartphone Use

<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.