By: Jessica San Luis
When speaking of the exigencies faced by incarcerated individuals, the lived experiences of
adolescents within the carceral system are of particular concern. More than 87% of
juveniles involved in the criminal justice system have suffered some form of childhood
trauma, whether that is physical, emotional or psychological violence or abuse; substance
abuse or addiction issues; poverty and food instability; or caregiver incarceration. These
young people are trapped in between functioning as adults and growing as children, and
because of this are both deeply vulnerable and utterly rehabilitatable. And while states
must weigh community safety against alternatives to incarceration, when the subjects are
children, the litmus test for basic humanity must be reevaluated.
Over two decades of developmental neuroscience research have shown that the human
brain—especially the frontal lobe and prefrontal cortex—continues to develop well into the
mid-twenties. This has significantly shaped modern legal and psychological understanding
of adolescent behavior. Individuals under 25 lack fully mature neural systems responsible
for judgment, impulse control, future planning, and risk assessment, which reduces their
moral and criminal culpability compared to fully developed adults.
The prefrontal cortex governs executive functions such as decision-making, inhibition of
impulses, and long-term reasoning. Multiple neuroimaging studies demonstrate that this
region is among the last to reach full structural maturity. Giedd et al. (1999) first
established through longitudinal MRI scans that frontal lobe development continues into
the third decade of life. Subsequent work by Sowell et al. (2001, 2003) and Casey, Jones &
Hare (2008) confirmed that key neural pathways—including white matter tracts associated
with self-regulation—undergo substantial myelination and synaptic pruning until
approximately age 25.
In contrast, systems responsible for emotional reactivity and reward-seeking, including the
amygdala and nucleus accumbens, mature earlier and often display heightened sensitivity
during adolescence and young adulthood (Steinberg, 2008; Galván et al., 2006). This
creates what researchers call the “dual systems” model: a mismatch between a highly active
reward system and an underdeveloped regulatory system. As a result, individuals under 25
show increased impulsivity, heightened susceptibility to peer pressure, reduced capacity to
consider future consequences, and more emotionally driven decision-making.
These developmental characteristics have direct implications for criminal law. Fundamental
principles of culpability rely on an individual’s capacity for reasoned judgment, impulse
control, and foresight. But because young people generally lack fully mature neurological
systems, their decision-making is less stable, more context-dependent, and more externally
influenced than that of adults. As Laurence Steinberg (2009) notes, traits such as
impulsivity and risk-taking are “developmentally normative” and typically diminish as the
brain matures, underscoring youth’s greater capacity for change.
Similarly, the United States Supreme Court has repeatedly relied on this scientific
consensus as a bright line rule for review of cases involving juvenile defendants. In Roper v.
Simmons, 543 U.S. 551 (2005), the Supreme Court summarily rejected capital punishment
in juvenile cases, citing adolescents’ reduced maturity, vulnerability to external pressures,
and developing character. In Graham v. Florida, 560 U.S. 48 (2010), the Court issued a
prohibition on life without parole (LWOP) for non-homicide offenses where the defendant
was a juvenile at the time of commission, again relying heavily on neuroscience of
immaturity. And finally, in Miller v. Alabama, 567 U.S. 460 (2012), the Court universally
rejected the practice of mandatory life sentences without parole for juvenile defendants,
emphasizing that neurological differences make youth less culpable and more capable of
reform. In fact, in a subsequent ruling, the Court in Montgomery v. Louisiana, 577 U.S. 190
(2016), reaffirmed Miller, noting that that adolescents are constitutionally less deserving of
the harshest punishments due to their underdeveloped brains.
Although these cases focus on individuals under 18, established neurological research
shows that the same developmental principles extend through – and possibly beyond – age 25 Emerging adults share similar immaturity in executive function and impulse control,
suggesting that their culpability is similarly diminished and that sentencing should reflect
their ongoing development and capacity for change. For emerging adults, like the majority
of those currently funneling through the ineluctable justice machine, who lack basic
education, family resources and are significantly emotionally and psychologically
vulnerable because of chronic and generational trauma, the developmental delays and
dysfunction are even more pronounced. This is the most vulnerable demographic within
the justice ecosystem, specifically because these children are teetering on the complicated
precipice between adolescence and adulthood: ironically both uniquely susceptible to
dysfunctional behaviors and amenable to rehabilitation. And while the courts and
individual states have embarked upon a slow roll towards substantive juvenile justice
reform, the 32,000 currently incarcerated adolescents, time is quite literally running out.
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