Reversing anterior insular cortex neuronal hypoexcitability attenuates compulsive behavior in adolescent rats

From compulsivity to compulsion: the neural basis of compulsive disorders

Compulsive behaviour, an apparently irrational perseveration in often maladaptive acts, is a potential transdiagnostic symptom of several neuropsychiatric disorders, including obsessive-compulsive disorder and addiction, and may reflect the severe manifestation of a dimensional trait termed compulsivity. In this Review, we examine the psychological basis of compulsions and compulsivity and their underlying neural circuitry using evidence from human neuroimaging and animal models. Several main elements of this circuitry are identified, focused on fronto-striatal systems implicated in goal-directed behaviour and habits. These systems include the orbitofrontal, prefrontal, anterior cingulate and insular cortices and their connections with the basal ganglia as well as sensoriomotor and parietal cortices and cerebellum. We also consider the implications for future classification of impulsive-compulsive disorders and their treatment.

Propensity for risky choices despite lower cue reactivity in adolescent rats

Adolescence is a time of heightened risk-taking across species. Salient audiovisual cues associated with rewards are a common feature of gambling environments and have been connected to increased risky decision-making. We have previously shown that, in adult male rats, sign tracking - a behavioral measure of cue reactivity - predicts an individual's propensity for suboptimal risky choices in a rodent gambling task (rGT) with win-paired cues. However, adolescents perform less sign tracking than adult animals, suggesting that they are less cue-reactive than adults in some circumstances. Therefore, we investigated the performance of adolescent male rats on the rGT with win cues and examined its relationship with their sign-tracking behavior. We found that adolescents make more risky choices and fewer optimal choices on the rGT compared with adults, evidence of the validity of the rGT as a model of adolescent gambling behavior. We also confirmed that adolescents perform less sign tracking than adults, and we found that, unlike in adults, adolescents' sign tracking was unrelated to their risk-taking in the rGT. This implies that adolescent risk-taking is less likely than that of adults to be driven by reward-related cues. Finally, we found that adults trained on the rGT as adolescents retained an adolescent-like propensity toward risky choices, suggesting that early exposure to a gambling environment may have a long-lasting impact on risk-taking behavior.

Early-onset smoking theory of compulsivity development: a neurocognitive model for the development of compulsive tobacco smoking

According to the literature, individuals who start tobacco smoking during adolescence are at greater risk of developing severe tobacco addiction and heavier smoking behavior in comparison with individuals who uptake tobacco smoking during subsequent developmental stages. As suggested by animal models, this may be related to the unique neuroadaptive and neurotoxic effects of nicotine on adolescents' fronto-striatal brain regions modulating cognitive control and impulsivity. Previous research has proposed that these neuroadaptive and neurotoxic effects may cause a heightened reward-oriented impulsive behavior that may foster smoking relapses during quit attempts. However, developments in the field of addiction neuroscience have proposed drug addiction to represent a type of compulsive behavior characterized by the persistent use of a particular drug despite evident adverse consequences. One brain region that has received increased attention in recent years and that has been proposed to play a central role in modulating such compulsive drug-seeking and using behavior is the insular cortex. Lesion studies have shown that structural damages in the insular cortex may disrupt smoking behavior, while neuroimaging studies reported lower gray matter volume in the anterior insular cortex of chronic smokers compared with non-smokers, in addition to correlations between gray matter volume in the anterior insular cortex and measures of compulsive cigarette smoking. Based on the findings of our recent study reporting on early-onset smokers (mean age at regular smoking initiation = 13.2 years) displaying lower gray matter and white matter volume in the anterior insular cortex compared to late-onset smokers (mean age at regular smoking initiation = 18.0 years), we propose that the anterior insular cortex may play a central role in mediating the association between smoking uptake during adolescence and smoking heaviness/tobacco addiction during adulthood.