Diminished brain thickness in teens tied to impulsivity

In adolescents, diminished cortical thickening in brain networks involved in value-based decision making—specifically, the ventromedial prefrontal and orbitofrontal cortices—may be associated with impulsive choices, according to a new study published in The Journal of Neuroscience.

“Moving forward, such neuroanatomical markers of impulsivity may aid in the development of personalized interventions targeted to reduce risk of negative outcomes resulting from impulsivity during adolescence,” wrote lead author Marieta Pehlivanova, PhD, Department of Psychology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.

Adolescence is a vulnerable period and risky behaviors, such as drug use, reckless driving, and unprotected sex, can threaten well-being. Some researchers suggest that risk experienced during adolescence impacts brain development. Specifically, risk may cause differential maturation of the reward processing regions, including the orbitofrontal cortex and ventral striatum, and cognitive control regions, such as the dorsolateral prefrontal cortex.

One commonly used index of impulsive choice is delay discounting (DD), which measures impulsivity. In this study, DD was measured using a task that posed 34 self-paced questions made between a smaller reward delivered sooner versus a bigger reward delivered later. Of note, the researchers didn’t give out tangible rewards; instead, the rewards were hypothetical.

Delay discounting engages areas of the brain known to mature at different rates in adolescents, such as the dorsolateral prefrontal cortex (dlPFC), orbitofrontal cortex, and ventral striatum.

“At present, it remains relatively unknown how individual differences in structural brain development may relate to DD in adolescents,” wrote the authors. “We hypothesized that we would find associations between DD and CT in brain regions associated with reward processing, such as the ventromedial prefrontal cortex (vmPFC), as well as regions subserving cognitive control (eg, dlPFC).”

The researchers based their final analysis on a subsample of 427 participants (average age: 17 years, n=208 men) from the Philadelphia Neurodevelopment Cohort (PNC). All participants in PNC underwent neurocognitive assessment and CT neuroimaging.

The researchers examined associations between DD and cortical thickness on CT within structural covariance networks. They found diminished CT thickness in the vmPFC, orbitofrontal cortex, temporal pole, and temporoparietal junction. These regions play a role in value-based decision making. They suggest diminished cortical thickness is a marker for impulsive choice during this vulnerable period in adolescence.

The researchers also found that structural brain networks better predicted DD than did cognitive and demographic variables.

Of note, associations between DD and cortical thickness did not change with respect to age range or other confounding variables.

One limitation of this study was that, because decreased cortical thickness in regions linked to impulsive choice were independent of age, it’s possible that these outcomes may emerge earlier than in the age ranges examined by the researchers. Future research could examine such changes using a longitudinal design starting in early childhood.

“Moving forward, such brain-based measures could potentially be used as biomarkers to identify youth at particularly high risk for negative outcomes,” conclude the researchers. “Future studies should evaluate associations between DD, brain structure, and psychopathology.”