Newswise — The brain responds to rewarding stimuli by increasing the release of a neurotransmitter called dopamine. When we feel motivated, it is because our brain anticipates this dopamine reward.

The transition from early to mid-adolescence is associated with increased reward sensitivity and reward-seeking behavior, a consequence of normal brain development. This heightened sensitivity or prioritization of reward can be thought of as reflecting a greater motivation to obtain rewards. A new study, published in Alcoholism: Clinical and Experimental Research, has addressed whether drinking alcohol in early adolescence might impact the brain’s reward systems, by examining associations between alcohol initiation and subsequent changes in reward motivation while accounting for baseline scores. Differences between boys and girls were also evaluated.

Researchers from the universities of George Mason (Fairfax, VA), Yale (New Haven, CT), and Pennsylvania State (University Park, PA) analyzed data from around two hundred adolescents, recruited when aged 11-14 years and followed up for 3 years (to age 14-17. None had started using alcohol at the study outset, and all completed a yearly survey to report on alcohol use during follow-up. Reward motivation was measured at baseline and after 3 years using two methods. The first, a self-report survey, assessed levels of drive, fun-seeking, and reward-responsiveness. For the second, a task to measure bias towards immediate reward, participants chose between a smaller, immediate monetary reward (fluctuating between 0 and $10 across numerous trials) and a $10 delayed reward to be provided after 0, 2, 30, 180, or 365 days. The point at which the participant considered the immediate and delayed rewards as equally as attractive was calculated.

By year 3, 30% of participants had started to use alcohol. Using statistical modelling, the researchers showed that alcohol initiation during this period of early adolescence was associated with greater levels of self-reported reward motivation at 3 years, as assessed by the fun-seeking (but not the drive or reward-responsiveness) measure, which may capture key aspects of impulsivity. On the task-based measure, alcohol initiation predicted a higher bias at year 3 towards immediate reward, but only in boys.

This study is the first to show changes in reward motivation over time following adolescent alcohol initiation. The researchers propose that alcohol may be associated with changes in adolescent brain structure or function involved in evaluating reward. However, it is possible that alcohol initiation does not itself impact the brain, but reflects other processes, in that individuals who are temperamentally driven to experience increases in reward motivation from early to mid-adolescence might also be more likely to initiate alcohol use during this time. The findings might explain the sensitivity of the adolescent brain to alcohol’s effects during development and, as neurological reward processes are central to addiction, could help untangle the relationship between early alcohol use and later alcohol abuse.

Does alcohol initiation in early to middle adolescence predict changes in reward motivation? Evidence of sex differences. K.L. Mauro, S.F. Goncalves, R. Sinha, E. Ansell, T.M. Chaplin (pages xxx)