Commentary on the special issue "The Adolescent Brain": How can we run operant paradigms in a preclinical adolescent model? Technical tips and future perspectives

Adolescents rats engage the orbitofrontal-striatal pathway differently than adults during impulsive actions

Adolescence is characterized by increased impulsive and risk-taking behaviors. To better understand the neural networks that subserves impulsivity in adolescents, we used a reward-guided behavioral model that quantifies age differences in impulsive actions in adult and adolescent rats of both sexes. Using chemogenetics, we identified orbitofrontal cortex (OFC) projections to the dorsomedial striatum (DMS) as a critical pathway for age-related execution of impulsive actions. Simultaneous recording of single units and local field potentials in the OFC and DMS during task performance revealed an overall muted response in adolescents during impulsive actions as well as age-specific differences in theta power and OFC-DMS functional connectivity. Collectively, these data reveal that the OFC-DMS pathway is critical for age-differences in reward-guided impulsive actions and provide a network mechanism to enhance our understanding of how adolescent and adult brains coordinate behavioral inhibition.

Sex Differences in Risk Preference and c-Fos Expression in Paraventricular Thalamic Nucleus of Rats During Gambling Task

Different biological requirements between males and females may cause sex differences in decision preference when choosing between taking a risk to get a higher gain or taking a lower but sure gain. Several studies have tested this assumption in rats, however the conclusion remains controversial because the previous real-world like gambling tasks contained a learning component to track a global payoff of probabilistic outcome in addition to risk preference. Therefore, we modified a simple gambling task allowing us to exclude such learning effect, and investigated the sex difference in risk preference of rats and its neural basis. The task required water deprived rats to choose between a risky option which provided four drops of water or no reward at a 50% random chance vs. a sure option which provided predictable amount x (x = 1, 2, 3, 4). The amount and the risk were explicitly instructed so that different choice conditions could be tested trial by trial without re-learning of reward contingency. Although both sexes correctly chose the sure option with the same level of accuracy when the sure option provided the best offer (x = 4), they exhibited different choice performances when two options had the same expected value (x = 2). Males and females both preferred to take risky choices than sure choices (risk seeking), but males were more risk seeking than females. Outcome-history analysis of their choice pattern revealed that females reduced their risk preference after losing risky choices, whereas males did not. Rather, as losses continued, reaction time for subsequent risky choices got shorter in males. Given that significant sex difference features mainly emerged after negative experiences, male and female rats may evaluate an unsuccessful outcome of their decision in different manners. Furthermore, c-Fos expression in the paraventricular nucleus of the thalamus (PV) was higher in the gambling task than for the control task in males while c-fos levels did not differ in females. The present study provides a clear evidence of sex differences in risk preference in rats and suggests that the PV is a candidate region contributing to sex differences in risky decision making.

Internet Addiction in adolescence: Neurobiological, psychosocial and clinical issues

Despite it has not been formally included in DSM-5 as a disorder, 'Internet addiction (IA)' has become a worldwide issue. It can be broadly defined as a non-chemical, behavioral addiction, which involves human-machine interaction. We pinpoint it as an "instrumental" form of social interaction (i.e. mediated by machines), a notion that appears useful for the sake of possible preclinical modeling. The features of Internet use reveals as addictive when this comes at the expense of genuine real-life sociability, with an overlap towards the hikikomori phenomenon (i.e., extreme retreat to one's own room). Due to the specific neuro-developmental plasticity in adolescence, IA poses risks to youths' mental health, and may likely produce negative consequences in everyday life. The thwarted development of adolescents' identity, self-image and adaptive social relationships is discussed: the IA adolescents often suffer loss of control, feelings of anger, symptoms of distress, social withdrawal, and familial conflicts. Further, more severe clinical conditions are also associated to IA, such as dysthymic, bipolar, affective, social-anxiety disorders, as well as major depression. This paper overviews the literature on IA, from neuro-biological, psycho-social and clinical standpoints, taking into account recent debates on diagnostic criteria, nosographic label and assessment tools. Neuroimaging data and neurochemical regulations are illustrated with links to pathogenetic hypotheses, which are amenable to validation through innovative preclinical modeling.