The literature is equivocal regarding the role of internalizing problems in the etiology of adolescent substance use. In this study, we examined the association of internalizing and externalizing behavior problems and their co-occurrence with early adolescent substance use to help clarify whether internalizing problems operate as a risk or protective factor. A large community sample (N=387; mean age at the first assessment 12 years old; 83 % White/non-Hispanic) was assessed annually for 3 years. Externalizing problem behavior in the absence of internalizing problems showed the strongest prospective association with alcohol, cigarette, and marijuana use. A weaker, albeit statistically significant prospective positive association was found between co-occurring internalizing and externalizing behavior problems and substance use. Internalizing problems in the absence of externalizing problems protected adolescents against cigarette and marijuana use. Clarifying the role of internalizing problems in the etiology of adolescent substance use can inform the development of early intervention and prevention efforts. Our results highlight the importance of further considering the co-occurrence of internalizing and externalizing behavior problems in developmental pathways to substance use.

Movement representations in the motor cortex can reorganize to support motor skill learning during young adulthood. However, little is known about how motor representations change during aging or whether their change is influenced by continued practice of a skill after it is learned. We used intracortical microstimulation to characterize the organization of the forelimb motor cortex in young and aged C57/BL6 mice after short (2-4 weeks) or long (8 weeks) durations of training on a skilled reaching task or control procedures. In young mice, a short duration of reach training increased the area of proximal forelimb movement representations at the expense of distal representations. Following a longer training duration, ratios of proximal to distal movements returned to baseline, even with ongoing practice and skill maintenance. However, lingering changes were evident in thresholds for eliciting distal forelimb movements, which declined over the longer training period. In aged mice, movement representations and movement thresholds failed to change after either duration of training. Furthermore, there was an age-related loss of digit representations and performance decrements on other sensorimotor tests. Nevertheless, in quantitative measures of reaching success, aged mice learned and performed the skilled reaching task at least as well as younger mice. These results indicate that experience-driven topographical reorganization of motor cortex varies with age, as well as time, and is partially dissociable from behavioral performance. They also support an enduring capacity to learn new manual skills during aging, even as more youthful forms of cortical plasticity and sensorimotor function are lost.

The present study supported the validity of a model with both a general PD impairment dimension and separate individual difference dimensions; however, it also indicated that currently prominent models, which assume general PD impairments and personality traits are non-overlapping, may be misspecified.

Externalizing problem behavior is a robust predictor of early adolescent substance use (SU); however findings regarding internalizing problems have been mixed, suggesting that there may be important moderators of the relationship between internalizing problems and SU. The present study used a community sample (mean age was 12.1 at the first assessment, 55% female, 83% White) to test a longitudinal latent variable interaction structural equation model to examine whether externalizing problems moderated the relationship between internalizing problems and SU. Peer delinquency was tested as a mediator in the model and prior levels of the mediator and outcome were controlled at each wave to establish temporal precedence. Results suggested that (1) internalizing problems were protective against associating with deviant peers, but only at high levels of externalizing symptomatology, (2) higher levels of peer delinquency were associated with increases in SU, and (3) peer delinquency mediated the effect of the problem behavior interaction on SU. Our findings suggest that the impact of internalizing problems on peer delinquency and SU needs to be considered in the context of externalizing problems. Moreover, developmental models involving internalizing symptoms should consider that internalizing symptoms are generally protective against substance use in early adolescence.

Prior work has suggested a paradoxical positive relationship between the risk behavior alcohol use and the health behavior exercise, particularly in young adults. Though seldom tested, different theoretical perspectives exist on the mechanisms that may explain the positive relationship. The aims of this study were to test theorized mechanisms of association, including common causes shared by both behaviors (e.g., personality, motives, affective), compensatory processes such as exercising to compensate for calories from alcohol consumption, and methodological confounds (e.g., between vs. within subject effects) in a college sample (N = 132; 56.3% male; 76% Caucasian; M = 19.15, SD = 0.99) using a cross-sectional design and time line follow back methods. A positive, between-subjects association between alcohol and exercise was found and explained by exercising to compensate for calories of alcohol consumption, enhancement motives, and physical activity enjoyment. However, we also observed a significant and negative within-subjects association between the two constructs, suggesting that, on a given day, individuals who exercise more tended to drink less. Furthermore, individuals who exercised more during the week tended to have declines in weekend drinking over time. Results suggest a complex relationship between exercise and alcohol use among young adults, and highlight the importance of distinguishing between and within subject processes, as well as the temporal ordering of the two behaviors. Implications are discussed in regard to theory, prevention, and intervention.