Specifically, more than half of adolescents have tried at least one substance by age 18, with many using at least one substance in a “harmful way”, such as binge use. Due to the inherently illicit behaviors that must be engaged in to access and utilize most substances, many youth use substances in ways that increase the likelihood of encountering other forms of harm . In terms of health relevance, large-scale data reflect that health sequelae for substance use for adolescents have become much more severe throughout the past three decades. Not only does morbidity and mortality increase 200-300% during this developmental period , but a recent JAMA review indicates that alcohol use increased morbidity from 5,800 deaths in 1980 to 9,400 deaths in 2014, with years of life lost doubling . Further, substance-related consequences have skyrocketed from 3,300 deaths in 1980 to 33,100 deaths in 2014, with years of life lost up by a factor of nine .Viner and colleagues utilize a metric that quantifies impact of adolescent exposure, referred to as adolescent attributable fraction . This represents the relative impact on mortality that would have occurred in the absence of exposure to the risk . In the example of tobacco, this team found that 80% of individuals commence tobacco use during adolescence, contributing to 72% of smoking during the adult years, with a pronounced link particularly for those who initiated smoking before age 16 . Additionally, a recent Lancet review highlighted that the ages of 15-19 are particularly precarious for adolescents throughout the globe,vertical grow with accidents and injuries as the top cause of death in this age group, and substance use itself a leading cause of disability . Despite several decades of efforts by experts to identify the best avenues to prevent and reduce adolescent substance use, progress continues to be limited.
Given that adolescents have goals, cognitions, and social contexts that are distinct from adults, one avenue that may improve treatment outcomes for this age group is considering substance use via a neurodevelopmental lens . Despite the rise of scientific interest in the neurodevelopmental period of adolescence , exemplified by recent large-scale research initiatives , throughout history contributions of this salient developmental period on health and neural drivers of behavior have largely been overlooked . This is relevant because adolescence is, at this moment, being recognized as a highly unique neurodevelopmental period that can impact lifelong health and well being – the chrysalis before adulthood. While much of the literature tends to focus on adolescents’ newly piqued penchant for risk behaviors, fewer clinical and research efforts have been dedicated to the highly adaptive aspects of the adolescent period . Data are now showing that the adolescent brain is, in many ways, pre-programmed for resilience , with the adolescent brain purposefully transitioning from an over proliferation of neurons, characteristic of childhood, to greater specificity and focus of brain networks, demonstrated by increases in strength and purpose . In lay terms, the adolescent brain can be seen as the development of a system of functional highways established within the brain during this developmental stretch. Ultimately, across theoretical perspectives, biology and environment dynamically interact throughout this time to generate an enhanced set of developmental tasks during this window; the outgrowth of which sets the foundation for later adaptive network connectivity, structure/function, and resultant behavior and cognition during adulthood. Gonadarche, the maturation of the gonads, follows adrenarche and is characterized by a surge of hormones and rapid physical growth, contributing to sexual dimorphism in the body, face and voice . Gonardarche begins in the brain, with hypothalamus release of gonadotrophin-releasing hormone , in turn activating the resting hypothalamic-pituitary-gonadal axis, and pituitary to produce folliclestimulating hormone and luteinizing hormone . FSH and LH generate estrogen and testosterone , instrumental in movement toward sexual dimorphism in the body and brain .
One particularly robust finding, relevant to the adolescent treatment context, is that pubertal maturation, particularly increased testosterone, promotes structural and functional development of the striatum . This is salient, as hormonally-mediated striatal development has been implicated as predictive of risk-taking and substance use during adolescence , above and beyond chronological age. This suggests that variability in gonadal hormones may play a crucial role in organizing striatal development and consequential reward-seeking behavior during adolescence; factors relevant in the adolescent addiction treatment context. While such striatal changes have been examined in the context of negative risk-taking, there is reason to believe that striatal changes also serve a vital role in positive risk-taking, including pursuit of goals and movement into more mature social and cognitive challenges . While the hormonal cascade has been established, how each element contributes to the nature of cognitive development and its intersection with adolescent mental health, including substance use and its treatment, has been under-examined . Here we highlight the central and interactive roles of DHEA and gonadal hormones in neurocognitive development, and indicate their potential role and impact within the adolescent addiction treatment context. Surge of cognitive skills. Another hallmark of adolescence is the steep improvement in cognitive abilities that allow individuals to set and accomplish high-level goals . In addition to the widely recognized role of cognitive control, adolescents show an elegant network of development across an array of cognitive skills during this period. Examples of emergent cognitive skills highly relevant to the treatment context include the inception of abstract reasoning, higher-order reasoning, working memory, self-monitoring, and cognitive flexibility . Of note, this array of cognitive skills matures across a range of timelines throughout adolescence. For example, cognitive flexibility is firmly online by early adolescence, whereas working memory shows strongest effects by late adolescence . Developmental neuroscientists propose that the heterogeneous patterns of behavior observed throughout adolescence are sub-served by the comparably heterogeneous patterns of brain development; this has direct implications for clinical treatment with adolescents.
A rich collection of functional neuroimaging studies in healthy adults compared with lesion patients reveal the centrality of prefrontal and parietal cortices in cognitive control and related cognitive capacities . Structural prefrontal and parietal cortical development is typified by cortical thinning in gray matter, along with linear increases in white matter. Marked regional variability is observed; medial and ventral prefrontal cortex develop notably sooner than lateral and dorsal PFC . Further, these patterns do not linearly associate with emerging cognitive skills. For example, cross-sectional studies of working memory and inhibitory control have, somewhat counter intuitively, shown both increases and decreases in activation of prefrontal and parietal cortex with age, depending on task demands and the precise adolescent age tested. This mirrors the adolescent substance use neuroimaging literature, which has shown the same pattern of counter intuitive increases and decreases in activation . One possibility is that age predicts stronger activation in a smaller,indoor growers more specialized subset of prefrontal and parietal regions, and less reliance upon more diffuse, and less task-relevant regions . Indeed, a growing number of longitudinal studies support “task-positive” activation increases, and in tandem, less task irrelevant activation, throughout adolescence . Of relevance to the treatment context, these disparate patterns of developmental timing may help explain why developing adolescent cognitive skills like working memory, which is supported by dlPFC , along with abstract thinking and reasoning, which rely upon the most rostral portions of dlPFC , emerge a bit later in the cognitive skill cascade. A challenge that stymies succinct characterization of adolescent cognitive development – and likely adolescent substance use treatment as well – is that the same adolescents often show markedly different cognitive skills when placed in different socio-emotional contexts. Relative to adults, adolescent performance is more strongly impacted by affectively salient stimuli and by socioemotional contexts . This sensitivity to socioemotional contexts is mirrored by the relatively greater responsivity of subcortical structures as compared with lateral prefrontal regions during this age period; relevant to the treatment context, these networks serve a crucial role in identifying and behaviorally responding to salient cues .
Importantly, turning up the socioemotional dial also impacts functional coupling in nascent prefrontal parietal and prefrontal-subcortical networks . These adolescent-specific differences in circuit-level communication may be crucial for understanding how and why adolescents identify emotions, particularly when emotions run hot . Similarly, adolescents differ significantly from adults in their emerging skills in engaging cognitive strategies, including reappraisal and emotional distancing, to regulate emotions . A long history of behavioral research has shown that very young children can utilize cognitive regulatory strategies if provided the appropriate scaffolding, but not necessarily when left to their own devices . Relevant to the treatment context, one’s ability to effectively engage cognitive strategies in the area of self-regulation improves linearly from childhood to adolescence, with performance plateauing at around age 17 . The precise age at which adolescents achieve adult-like performance differs for social and nonsocial stimuli , as well as for appetitive and aversive stimuli . Adolescents show protracted development, particularly in the context of salient, negative emotions , and in turn, adolescence is typified by a period of greater experienced negative affect and elevated amygdala response relative to adults . Compared to adolescents, adults show reduced concurrent and sustained amygdala responses to aversive stimuli, and these age-related reductions in amygdala response are mediated by the enhanced role of ventrolateral prefrontal cortex . However, the interaction between vlPFC and amygdala responses requires relatively mature prefrontal-amygdala coupling, suggesting that neurobiological development serves as a relevant potential rate-limiting step in adolescents’ ability to navigate certain types of strong emotions, and engage planful behavior in the context of deep negative feelings . Another central hallmark of adolescent cognitive development is the emergence of abstract reasoning . Of relevance to the treatment context, abstract reasoning enables an adolescent to generate and systematically evaluate hypotheses and engage in relational reasoning , which involves the simultaneous consideration of interrelated dimensions and situations necessary to arrive at a conclusion . Children can solve 0- and 1- relational level problems easily, but only adolescents with sufficient frontal lobe maturation have the capacity to solve 2-relational level problems, wherein two dimensions of variation are simultaneously considered . As behavioral treatment often requires this type of simultaneous processing, the development of this cognitive skill may impact adolescents’ capacity to engage and successfully participate in treatment. Together, the findings above suggest that adolescence is characterized by an array of novel cognitive skills highly relevant to the treatment context, including the emergent capacity to reason abstractly, to experience and react to negative emotions, and in turn, to develop and engage in purposeful and planful behavior. Many developing cognitive processes hinge upon the capacity for meta-cognition, including the capacity to self-reflect sufficiently in order to effectively self-monitor. This may explain why social and cognitive processes appear to co-develop behaviorally and neurally . Relative to children, in some of these dimensions, adolescents are more akin to adults in arenas of self-processing , subserved by the ventromedial prefrontal cortex and the ventral striatum . However, highly relevant to the adolescent treatment context, the vmPFC is uniquely sensitive to evaluating the self-relevance of social information during adolescence , while the VS is central to “what other people think about you”, a characteristic cognitive feature heightened during adolescence . While a heightened sense of self is normative during adolescence, the novel experience of self-reflection and self-monitoring has some unpleasant implications. Adolescents’ growing ability to consider what others think about them can be accompanied by natural elevations in attendant negative affect, including fears about social assessment and self-consciousness, both of which peak during adolescence . The enhanced feelings of others’ scrutiny can be activated even during minimally evaluative circumstances – such as simply telling a study participant that a peer is watching them– and has been linked to adolescent-specific increases in medial prefrontal cortex recruitment and mPFC-VS connectivity . Greater self-focus also has a darker side. It can lead to rumination, negative affect, and depression , and can contribute to adolescents’ sense that they need to engage in behaviors to improve their social standing and affect, including substance use . Together, relevant for the adolescent addiction treatment context, these data suggest that adolescent-emergence of self-focus is supported by functional changes in regions involved in self-cognition, and to a lesser extent – regions involved in cognitive and affective processing – and that these normative changes likely contribute to the characteristic pronounced self-focus experienced by most adolescents. Adolescents’ changing social landscape.