Abstract Exaggerated reactivity to drug-cues and emotional dysregulations represent key symptoms of early stages of substance use disorders. The diagnostic criteria for (Internet) Gaming Disorder strongly resemble symptoms for substance-related addictions. However, previous cross-sections studies revealed inconsistent results with respect to neural cue reactivity and emotional dysregulations in these populations. To this end the present fMRI study applied a combined cross-sectional and prospective longitudinal design in excessive online gamers (n=37) and gaming-naïve controls (n=67). To separate gaming-associated changes from predisposing factors, gaming-naive subjects were randomly assigned to 6 weeks of daily Internet gaming or a non-gaming condition. At baseline and after the training subjects underwent an fMRI paradigm presenting gaming-related cues and non-gaming related emotional stimuli. Cross-sectional comparisons revealed gaming-cue specific enhanced valence attribution and neural reactivity in a parietal network, including the posterior cingulate/precuneus in excessive gamers as compared to gaming naïve-controls. Prospective analysis revealed that six weeks of gaming elevated valence ratings as well as neural cue-reactivity in a similar parietal network, specifically the posterior cingulate/precuneus in previously gaming-naïve controls. Together, the prospective longitudinal design did not reveal supporting evidence for altered emotional processing of non-gaming associated stimuli in excessive gamers while convergent evidence for increased emotional and neural reactivity to gaming-associated stimuli was observed. Findings suggest that exaggerated neural reactivity in posterior parietal regions engaged in self-referential processing already occur during early stages of regular gaming probably promoting continued engagement in gaming behavior.