Motivational systems in adolescence: possible implications for age differences in substance abuse and other risk-taking behaviors

Abstract

Adolescence is an evolutionarily conserved developmental phase characterized by hormonal, physiological, neural and behavioral alterations evident widely across mammalian species. For instance, adolescent rats, like their human counterparts, exhibit elevations in peer-directed social interactions, risk-taking/novelty seeking and drug and alcohol use relative to adults, along with notable changes in motivational and reward-related brain regions. After reviewing these topics, the present paper discusses conditioned preference and aversion data showing adolescents to be more sensitive than adults to positive rewarding properties of various drugs and natural stimuli, while less sensitive to the aversive properties of these stimuli. Additional experiments designed to parse specific components of reward-related processing using natural rewards have yielded more mixed findings, with reports of accentuated positive hedonic sensitivity during adolescence contrasting with studies showing less positive hedonic affect and reduced incentive salience at this age. Implications of these findings for adolescent substance abuse will be discussed.

Figure 1

Adolescent (black circles) and adult (white circles) male rats were exposed to an autoshaping procedure in which an 8-sec presentation of an illuminated lever (the conditioned stimulus) was followed by response-independent delivery of a banana pellet. Rats were given 25 lever-pellet pairings each day, for a total of 5 days. The total number of times the lever was pressed was recorded for each session, with the mean (± standard error) number of lever presses for each group shown across the 5 conditioning days.