Orbitofrontal gray matter deficits as marker of Internet gaming disorder: converging evidence from a cross- sectional and prospective longitudinal design Feng Zhou 1 **, Christian Montag 1,2 ** , Rayna Sariyska 2 , Bernd Lachmann 2 , Martin Reuter 3,4 , Bernd Weber 4,5,6 , Peter Trautner 5 , Keith M. Kendrick 1 , Sebastian Markett 3,4 & Benjamin Becker 1 Key Laboratory for NeuroInformation, Center for Information in Medicine, School of Life Science and Technology, University of Electronic Science and Technology of China, China 1 , Institute of Psychology and Education, Ulm University, Germany 2 , Department of Psychology, University of Bonn, Germany 3 , Center for Economics and Neuroscience, University of Bonn, Germany 4 , Department for NeuroCognition, Life & Brain Center, Germany 5 and Department of Epileptology, University Hospital of Bonn, Germany 6 ABSTRACT Internet gaming disorder represents a growing health issue. Core symptoms include unsuccessful attempts to control the addictive patterns of behavior and continued use despite negative consequences indicating a loss of regulatory con- trol. Previous studies revealed brain structural deficits in prefrontal regions subserving regulatory control in individuals with excessive Internet use. However, because of the cross-sectional nature of these studies, it remains unknown whether the observed brain structural deficits preceded the onset of excessive Internet use. Against this background, the present study combined a cross-sectional and longitudinal design to determine the consequences of excessive online video gaming. Forty-one subjects with a history of excessive Internet gaming and 78 gaming-naive subjects were enrolled in the present study. To determine effects of Internet gamingon brain structure, gaming-naive subjects were randomly assigned to 6 weeks of daily Internet gaming (training group) or a non-gaming condition (training control group). At study inclusion, excessive Internet gamers demonstrated lower right orbitofrontal gray matter volume compared with Internet gaming-naive subjects. Within the Internet gamers, a lower gray matter volume in this region was associated with higher online video gamingaddiction severity. Longitudinal analysis revealed initial evidence that left orbitofrontal gray matter volume decreased during the training period in the training group as well as in the group of excessive gamers. Together, the present findings suggest an important role of the orbitofrontal cortex in the development of Internet addiction with a direct association between excessive engagement in online gaming and structural deficits in this brain region. Keywords brain structure, Internet addiction/Internet gaming disorder, orbitofrontal cortex, prospective design. Correspondence to: Christian Montag; Benjamin Becker: Key Laboratory for NeuroInformation, Center for Information in Medicine, University of Elec- tronic Science and Technologyof China, No.2006, Xiyuan Ave, West Hi-Tech Zone, 611731 Chengdu, China; Christian Montag: Institute of Psychology and Education, Ulm University, Helmholtzstr. 8, 89069 Ulm, Germany. E-mail: christian.montag@uni-ulm.de; ben_becker@gmx.de The work was carried out at: Institute of Psychology and Education, Ulm University, Ulm, Germany; Department of Psychology, University of Bonn, Bonn, Germany. ** shared first authorship INTRODUCTION During the last decade, the availability of high-speed Internet has grown on a global scale. While the techno- logical infrastructure has afforded tremendous oppor- tunities, these have come together with the cost of potential negative consequences in terms of excessive or even addictive patterns of Internet use, which can interfere with aspects of daily life, such as academic performance, health, and social activities (Kuss 2013). Although there is still no consensus about the gold standard for the assessment of addictive behavior in this context, the available epidemiological data suggest a rapidly emerging public health issue with growing ORIGINAL ARTICLE doi:10.1111/adb.12570 © 2017 Society for the Study of Addiction Addiction Biology