Three new studies appearing in Teenage Brains: Think Different?, a special issue of the journal Developmental Neuroscience, offer unprecedented insights into brain mechanisms that may predispose teenage boys to risky behaviors and an unhealthy disregard for disincentives and punishment.
The first study led by Michael Dreyfus and B.J. Casey of the Sackler Institute at Weill Cornell Medical College shows that adolescents, especially males, react to threat rather than withdraw from it, even when instructed to do otherwise. Volunteers were asked not to attend or respond to cues previously associated with an uncertain threat (e.g. a fearful face) while their brain was being imaged in a MR scanner. Adolescents, unlike children or adults, and adolescent males more so than adolescent females, impulsively reacted to these cues. This behavior in teenage males was paralleled by enhanced activity in the limbic brain or the emotional brain, which undergoes significant rewiring and remodeling of connections during adolescence.
The second study led by Jill Grose-Fife of John Jay College of Criminal Justice showed that adolescent males are relatively insensitive to punishment or losses, but hypersensitive to large gains. Brain activity was measured during small or large gains or losses during a gambling task, and the study found that adolescent males showed insensitivity to losses but hypersensitivity to large gains. These findings call into question the effectiveness of punishment as a deterrent for risky or deviant behaviors in adolescents.
A third study led by PhD student Iva Dincheva and Professor Francis Lee of Weill Cornell Medical College identifies brain-derived neurotrophic factor, a molecule known to regulate brain plasticity and learning, as a key to learning to fear dangerous situations. When adult mice are placed into a cage where they receive a mild foot shock, they learn to become afraid of being placed into that cage. However, adolescent mice don't show fear when placed back into that cage. Interestingly, when these same mice are returned to the same cage as adults, the fear response is evident. Dincheva and Lee show that neurotrophic factors are required to develop this unique fear response. When the authors artificially impaired neurotrophic factor signaling, the mice didn't show fear even as adults - they remained fearless both as adolescents and adults. In other words, the healthy respect for fearful stimuli encountered in teenage years, which is common among adults, requires intact neurotrophin signaling in the young brain, when the fearful stimuli are first encountered.