This is the first structural brain imaging study of cortical thickness in adolescents with internet addiction. Consistent with our hypothesis, the results indicated a reduced thickness of OFC in the internet addiction group compared to healthy controls. This finding is in accord with the results of former neuroimaging studies of internet addiction [9–14], and supports the theoretical model of addiction disorders, which emphasizes the involvement of the OFC.
The current finding on internet addiction supports the results of former studies on substance addiction, including ours , that have argued that the right OFC plays an important role in the biological mechanism of addiction disorders more broadly. The result of this study is not only in line with numerous other findings in the literature implicating the role of the OFC in addiction [4–6], but also with those indicating that this brain region in the right hemisphere might be particularly important .
In this study, only the lateral and not the medial OFC was shown to be significantly different in adolescents with internet addiction. The reason for this finding is not clear, but there have been multiple studies reporting different functions between the lateral and medial OFC, especially in reward-associated decision-making . For example, the medial OFC has been found to be preferentially activated in choices involving immediate rewards, whereas the lateral OFC has been implicated in choices concerning delayed rewards or suppression of previously rewarded responses [23, 24]. It is noteworthy that pars orbitalis, which is laterally adjacent to the lateral OFC, also showed significant cortical thinning in adolescents with internet addiction. This finding supports that the cortical thinning is particularly located in the lateral part of the OFC, without or less involving medial OFC. Further work is warranted on potentially different lateral and medial OFC functions.
Lateral OFC has also been implicated in cognitive flexibility deficits and in the genesis of pathological habits . In this regard, Chamberlain and colleagues (2008) demonstrated that the lateral OFC can be central to neurobiological models of obsessive-compulsive disorder (OCD) . Behavioral addictions are often considered to share similar features with other known disorders including OCD , involving specific difficulties in refraining from a certain behavior that causes serious personal consequences. Rotge and colleagues (2008, 2010), based on their previous meta-analyses [27, 28], investigated overlapping brain regions between the anatomical and functional brain maps that showed significant gray matter density change and activity during symptom provocation, respectively, in patients with OCD: the authors found that the only overlapping brain region was the lateral OFC. Recently, Zhou and colleagues (2012) have shown impaired mental flexibility along with poor response inhibition in young adults with internet addiction . The implications of reduced cortical thickness in lateral OFC, in relation to its role in internet addiction as well as other conditions with similar neurobehavioral features, are subject to future studies.
The present study has some important limitations. Above all, a different age distribution between the groups was a critical limitation of this study. However, previous reports on normal brain development have shown that cortical thickness peaks at approximately 8–9 years of age and then global cortical thinning begins afterward . Of note is that all the participants in our study were over this age. Therefore, in adolescents, younger individuals tend to have thicker cortex; our finding of thinner right OFC in the younger internet addiction group thus suggests that the age difference in groups was unlikely to have affected the results. Second, we did not measure the duration of internet addiction. Third, the study participants in the internet addiction group were excessive online gamers, and therefore, the current findings may entail limited generalizability to other subtypes of internet addiction .
In summary, the results of the present study indicate preliminary findings of reduced thickness of the right OFC in adolescents with internet addiction. The findings are further suggestive of a shared neurobiological mechanism between internet addiction and other addictive disorders.