Public Health Implications of Raising the Minimum Age of Legal Access to Tobacco Products (2015)

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The Developmental and Environmental Context of Adolescent and Young Adult Tobacco Use

Tobacco use is the result of a complex and dynamic interplay of multiple converging developmental, social, and environmental factors. Many of these factors are developmentally related, with adolescence and young adulthood as a key period of vulnerability to tobacco use and the progression to nicotine dependence (Jamner et al., 2003).

The development of adult decision-making skills and abilities is a continuous process that begins in early adolescence and continues into and through young adulthood, with no firm age periods for when specific developmental milestones occur. Furthermore, there are individual variations, with spurts of change and disjuncture resulting from social and environmental factors that influence the normative developmental process. These social influences are particularly salient in later adolescence and young adulthood.

Although previously considered a relatively short transition period, the late teens through the early 20s (ages approximately 18 to 26) is now considered a distinct period of life known as young adulthood (IOM and NRC, 2014). The newfound focus on this developmental period is due in part to prolonged education, delayed marriage, and delayed parenthood—events that historically marked adulthood, adult roles, and adult responsibility (Settersten and Ray, 2010)—and in part to studies showing that the brain continues to develop until the mid-20s (Giedd, 2008; Luna et al., 2004). Individuals in young adulthood face developmental and life changes that may make them particularly susceptible to drug use for several reasons: a desire to explore their identity, a response to the instability and disruption associated with life changes, or because of a tendency to focus on the pos-

sible positive consequences of drug use rather than negative consequences. Additionally, this is a time period when experimentation with risky behavior is most tolerated (IOM and NRC, 2014).

The unique psychosocial maturation of the adolescent and young adult developmental period, coupled with various environmental and social influences, results in a milieu that increases the desire for engaging in health-risk behaviors, including tobacco use. Furthermore, brain function and heightened sensitivity to nicotine characteristic of this period of development provides the biological context underlying the psychosocial and environmental influences related to adolescents’ and young adults’ decisions to start and continue to use tobacco.

The chapter begins with a review of the complex and layered cognitive, psychosocial, and biological aspects of adolescent and young adult development, with a focus on factors most likely to explain the heightened likelihood of tobacco initiation, continued use, and dependence. The chapter then ties these factors into the decision-making capabilities of adolescents and young adults. The chapter concludes with a discussion of the environmental context of tobacco use, including salient residential, school, and work changes and the role of tobacco marketing on adolescent and young adult tobacco use.

COGNITIVE, PSYCHOSOCIAL, AND BIOLOGICAL DEVELOPMENT IN ADOLESCENTS AND YOUNG ADULTS

Adolescence and young adulthood is a period of change with respect to cognitive, psychosocial, neurobiological, and physical development. These changes often result in increased vulnerabilities to using tobacco. These factors are reviewed next.

Cognitive Development

During adolescence, thinking becomes less concrete and more abstract, giving adolescents the ability to consider many components necessary for competent decision making at one time, consider potential positive and negative outcomes associated with each decision, and plan for the future. Studies have shown that by the time adolescents reach age 16, their general cognitive abilities, such as the ability to understand consequences—including the risks and benefits of their decisions—to process information, and to reason, are essentially identical to those of adults (Albert and Steinberg, 2011; Halpern-Felsher and Cauffman, 2001; Steinberg et al., 2009a). For example, in a study of 935 individuals ranging from age 10 to 30, Steinberg and colleagues (2009a) found no significant differences in cognitive skills between older adolescents (as young as ages 15–16) and adults.

Although there are individual differences and within-age-group variation, most adolescents reach a level of cognitive maturity comparable to adults by age 16. Despite the fact that cognitive maturity is reached by mid-adolescence, other aspects of psychosocial maturity, such as peer influence, sensation seeking, reward seeking, and impulse control, are still developing (as discussed later in this chapter). These different developmental systems explain in part why adolescents and young adults may have the cognitive ability to make safe and healthy decisions, yet are more prone than adults to make risky decisions. As shown below, even though adolescents have the ability to think abstractly and judge risks, they do not always adequately employ these abilities. Instead, adolescents are often seeking rewards and pleasures and therefore may decide to use tobacco despite knowing and understanding both the short-term and long-term risks.

Perceptions of Risks and Benefits

A hallmark of cognitive development is the ability to identify and understand consequences associated with a particular behavior. Perceptions of social, physical, and health risks associated with any given behavior as well as the perceived benefits, including both social and physical benefits, are key components of any competent decision. Research has shown that such perceptions actually predict the onset of behavior (Song et al., 2009b).

Adolescents, young adults, and adults are generally similar in their ability to identify and consider positive and negative consequences of their decisions. In some cases, adolescents actually perceive greater risks than do adults (e.g., Millstein and Halpern-Felsher, 2002). Several studies have shown that adolescents and young adults consider risks, benefits, and the value of behavior-related outcomes just prior to deciding on a particular behavior and that adolescents and young adults are keenly aware of risks (e.g., Halpern-Felsher and Cauffman, 2001; Lewis, 1981; Michels et al., 2005). In a review article, Albert and Steinberg (2011) concluded that there are few differences between the evaluations that adolescents (with ages varying depending on the study sample) and adults make of the risks inherent in various risky behaviors and few differences in their perceptions of the seriousness of these consequences (see also Kuther, 2003). Despite adolescents’ general understanding—and often overestimation—of risks, the perceptions of risks are only one part of the equation that adolescents and young adults use to make decisions. Adolescents naturally consider the importance of the social and physical benefits that they perceive they will gain from any given behavior (Song et al., 2009b). Furthermore, adolescents’ emotional immaturity and psychosocial factors influencing their behavior, such as impulsivity and peer pressure, often override the cognitive understanding of a risk.

Perceptions of Tobacco-Related Risks and Benefits Associated with Tobacco Use

Many studies have examined risk and benefit perceptions related to tobacco use. In general, studies show that people who smoke perceive less harm and greater benefits from cigarettes than do nonsmokers (Chassin et al., 2000; Fischhoff et al., 2010; Halpern-Felsher et al., 2004; Morrell et al., 2010; Soldz and Cui, 2002; Song et al., 2009b). Compared to nonsmokers, those who have smoked believe that they are less likely to experience long-term risks, such as lung cancer, heart attack, addiction, and death, and less likely to experience short-term consequences, such as smelling bad or having trouble breathing (Halpern-Felsher et al., 2004; Morrell et al., 2010; Song et al., 2009a). Smokers also believe that they are more likely to experience pleasure, feel relaxed, and “look cool” from smoking when compared to nonsmokers (Halpern-Felsher et al., 2004; Morrell et al., 2010; Song et al., 2009b). A prospective study of adolescents 14 to 16 years old demonstrated that perceptions of low long- and short-term risk and greater benefits predict the onset of tobacco use (Song et al., 2009b).

A much smaller body of work has examined whether perceptions of risks and benefits vary by type, brand, or packaging of the tobacco product. Historically, this research has focused on light and ultra-light cigarettes, with studies showing that most adults and adolescents incorrectly perceive that light cigarettes deliver less tar and nicotine, produce milder sensations, result in less health risk, and can make cessation easier (Etter et al., 2003; Gilpin et al., 2002; Kozlowski et al., 1998; Kropp and Halpern-Felsher, 2004; Shiffman et al., 2001; Tindle et al., 2006). More recent research has shown that consumers perceive that menthol-flavored cigarettes are less harmful than non-menthol-flavored cigarettes (Anderson, 2011; Klausner, 2011). Similarly, perceptions of the harms associated with snus (Choi et al., 2012; Øverland et al., 2008), smokeless tobacco (Callery et al., 2011), and cigars (Nyman et al., 2002) are lower compared to the perceived harms of cigarettes, and people perceive differences in risk based on type and color of product packaging (Bansal-Travers et al., 2011).

Psychosocial Development

In addition to developing the ability to consider the possible consequences of actions, including the likelihood and value of each consequence, adolescents and young adults are also maturing with respect to their psychosocial abilities. Psychosocial components relevant to tobacco decision making include social and peer comparison, sensation seeking and impulsivity, peer affiliation, susceptibility to peer pressure, the ability to understand and plan for the future, and perceived social norms.

While individuals vary even within the same age range, generally speaking most adolescents are on par with adults by age 16 with respect to thinking about the future (e.g., Albert and Steinberg, 2011; Halpern-Felsher and Cauffman, 2001; Steinberg et al., 2009b). However, other critical aspects of psychosocial development, such as those associated with peer pressure, sensation seeking, reward seeking, and impulse control, are much less developed during adolescence than during adulthood (Halpern-Felsher and Cauffman, 2001; Steinberg, 2008; Steinberg et al., 2008, 2009a; Zuckerman, 1979). “Dynamic accounts of factors that predict adolescent decisions” take into consideration the social, emotional, and self-regulatory factors that help explain why adolescents can make decisions just as rationally as adults, but often do not (Albert and Steinberg, 2011, p. 211). These areas of immaturity help explain why adolescents and young adults are more susceptible than older adults to initiating tobacco use.

Future Perspective Taking

Future perspective taking includes the ability to project into the future, to consider possible positive and negative outcomes associated with choices, and to plan for the future (Steinberg et al., 2009b), and is a hallmark of decision-making competence. Without an adequate understanding of future consequences and without the ability to have the future be part of present planning, it is more difficult to make decisions about behavior, including whether or not to use tobacco. It is not enough to have a working understanding of the possible risks and benefits that might come from using tobacco; it is equally important to be able to apply that information to making decisions about behaviors that could have an effect in the future. Steinberg and colleagues (2009b) found that the ability to plan for the future and to anticipate future consequences continues to develop through the mid-20s (see also Halpern-Felsher and Cauffman, 2001).

Sensation Seeking and Impulsivity

Sensation seeking refers to the drive to seek out experiences that are new, different, exciting, and highly stimulating as well as the willingness to take risks in order to have these experiences (Steinberg, 2008; Zuckerman, 1979). Higher sensation seeking is associated with drug use in early and middle adolescence (e.g., ages 12–16) (Kosten et al., 1994; Teichman et al., 1989) and with pubertal development; early maturers tend to rate higher on sensation-seeking scales and also on drug-seeking behavior (Martin et al., 2001; Steinberg, 2008). While sensation seeking follows a developmental trajectory, it is also viewed as a stable trait that is associated with risky behavior (Zuckerman, 2007).

Impulsivity refers to a tendency to make decisions in a quick fashion, without much thought or information. Impulsivity steadily declines from age 10 on (Steinberg et al., 2008). Becoming competent to make decisions requires that adolescents be able to control their desires and resist impulsive actions. Recent studies have highlighted the complex relationship among impulsivity, peer pressure, and delinquent behavior. Vitulano and colleagues (2010) have found that individuals with low impulsivity are actually more vulnerable to delinquent peer influences than those with high impulsivity. Thus, adolescents find themselves in a bit of a quagmire in that those with high impulsivity are likely to engage in risky behavior and those with low impulsivity are particularly sensitive to peer pressure that may also lead them to engage in risky behavior.

While impulsivity and sensation seeking are related, they are distinct features of decision making. Impulsive behavior may lead to experiences that are neither stimulating nor rewarding, and individuals may make the decision to engage in sensation-seeking behavior in a deliberate and non-impulsive manner (Steinberg et al., 2008). Additionally, while impulsive behavior decreases in a linear fashion from age 10 on, sensation-seeking patterns of development follow a curvilinear pattern in which sensation seeking increases between childhood and early adolescence and then either declines or remains stable in late adolescence and adulthood (Steinberg et al., 2008). For example, Steinberg and colleagues found that while 16- to 17-year-olds and 18- to 21-year-olds exhibit more impulse control than 10- to 15-year-olds, they exhibit significantly less impulse control than 22- to 25-year-olds and 26- to 30-year-olds.

Thus, adolescence and young adulthood is a time of low impulse control coupled with high rates of sensation seeking, which results in a greater likelihood that individuals in these development periods will engage in risky behavior. The coupling of low impulse control and high sensation seeking is especially harmful in more emotionally charged situations, in which adolescents are seeking rewards and pleasure yet do not have the ability to control these desires. Hence, adolescents are more likely to seek rewards such as those associated with tobacco use than they will be later in life, once the connections between their rewards pathways and impulse control are more in sync, which occurs in their mid-20s (Steinberg, 2013).

Social Norms

Social norms refer to common codes of behavior for a social group. The construct is used in a number of disciplines and theories of health behavior, including the Theory of Planned Behavior (Ajzen, 1985), Social Cognitive Theory (Bandura, 2001), and the Theory of Normative Social Behavior (Rimal and Real, 2005). Social norms are often classified as either descrip-

tive norms, which are perceptions of how people actually behave (which are often operationalized as perceived prevalence rates), and injunctive norms, which are perceptions of how people should behave (and are often operationalized by asking who would approve or disapprove of you engaging in a behavior) (Cialdini et al., 1990; Kallgren et al., 2000).

Both injunctive and descriptive norms are associated with smoking behaviors among adolescents and young adults. Alexander and colleagues (2001) analyzed data from the National Longitudinal Study of Adolescent Health and found that among 7th through 12th graders, adolescents in peer groups where 50 percent or more members smoked, or whose best friends smoked, were two times more likely to also smoke than those in peer groups in which fewer than half of the members smoked. Additionally, popular students who went to schools with higher smoking rates were more likely to smoke than non-popular students, while popular students in schools with low smoking rates were less likely to smoke. Etcheverry and Agnew (2008) found that among college students, friends, and romantic partners, smoking and injunctive norms were predictive of smoking behavior.

Peer Affiliation and Susceptibility to Peer Pressure

The ability to make rational decisions is mediated by a number of factors and, for adolescents, social factors in particular play a very large role in behavioral decision making. The transition to adolescence is marked by a decrease in time spent with parents and an increase in time spent either alone or with peers (Steinberg and Morris, 2001). This is a time period in which the opinions and actions of peers become increasingly important in influencing behavior (Crone and Dahl, 2012). Observational studies show that adolescents who engage in delinquent behavior are more likely to do so in groups (as opposed to adults, who are more likely to engage in delinquent behavior alone) (Albert et al., 2013; IOM and NRC, 2011; Zimring, 2000). Experimental studies have also shown that adolescents are more likely to make riskier decisions when they are told that they are being observed by peers than when they believe they are working alone (Albert et al., 2013). Compared with adults, adolescents exhibit exaggerated responses to positive social cues, and this reaction is coupled with more impulsive responses to stimuli (Albert et al., 2013; Gardner and Steinberg, 2005).

Generally, susceptibility to peer pressure that is undesirable or that goes against an individual’s goals decreases steadily from age 14 to 18 (Steinberg and Monahan, 2007). In order to make competent decisions, individuals must have the ability to resist undue pressure from others. That being said, studies also show that peers remain powerful influences and reinforcers of behavior even in late adolescence and young adulthood. For example, Duncan and colleagues found that males entering college with a history of

binge drinking were more likely to binge drink if they were paired with roommates who also binge drank in high school than they were if they were paired with a roommate who did not binge drink (Duncan et al., 2005). Furthermore, an experimental study assessing the differences in how peers influence risky behavior in adolescents (ages 13–16), young adults (ages 18–22) and adults (ages 24 and older) found that all three age groups made safe decisions when alone. However, in the presence of peers, both adolescents and young adults made risky decisions, with adolescents making riskier decisions than young adults, while adults, on average, made the safest decisions (Gardner and Steinberg, 2005).

Importance of Experience

Behavioral decisions and the perceptions of related outcomes are influenced by the extent to which a person has knowledge of and experience with the behavior or behavior-linked outcomes (Albert and Steinberg, 2011; IOM and NRC, 2004). Knowledge varies not only across ages but also within age groups. Adolescents and, to a lesser extent, young adults experience greater motivation to seek external rewards compared to adults, which results in this age group being more likely to exhibit approach behaviors (i.e., those driven by positive or desirable events or outcomes) than avoidance behaviors (i.e., those driven by negative or undesirable events or outcomes) (Elliot, 1999). Risk taking and sensation seeking can be viewed as part of this drive to experience potential rewards; thus, adolescence is a period in which individuals are particularly likely to initiate behaviors such as smoking (Lydon et al., 2014). This is particularly troubling because individuals who initiate smoking during adolescence are more likely to have a pleasurable first experience than individuals who initiate smoking in adulthood. Furthermore, studies show that pleasurable initial experiences are associated with rapid progression to regular smoking as well as continued smoking (DiFranza et al., 2007; Sartor et al., 2010).

In addition to the impact of having (or not having) direct personal experiences with particular consequences of behaviors, research has also investigated the effect of vicarious experiences, or knowledge about behaviors and related positive and negative outcomes experienced by others (Morrell et al., 2010). Applied to tobacco, adolescents and young adults rarely have knowledge of peers who have experienced tobacco-related disease, which lowers their perceptions of the likelihood of negative outcomes occurring after using tobacco (Morrell et al., 2010). When adolescents and young adults have had experience with tobacco-related illness, it is often in those much senior to them. Given their immature sense of the future and their ease at discounting the idea that what happens to others may also apply

to themselves, adolescents often do not apply the experiences of others to themselves (Morrell et al., 2010).

Additional Psychosocial Aspects of Young Adulthood

Later adolescence through young adulthood is a time of great demographic change and instability, including changes involving place of residence, employment, school attendance, and family formation, all of which play a substantial role in influencing tobacco use. Around age 18, most young people have moved away from home, and young adults continue to change residences more than any other age group (Arnett, 2000). In 2012, among adults ages 18 to 31, 23 percent were married and living in their own residence, 27 percent lived independently with others (i.e., cohabitating, living with a roommate or as a boarder, or in single parenthood), and fewer than 10 percent were living on their own (Fry, 2014). Young adults are also experiencing changes in their employment status, as they obtain various part-time or full-time jobs to earn money for school and living expenses, move, change colleges, and so on. Although employment rates among young adults have declined considerably over the past few decades, this decline has been largely offset by increases in educational attainment (IOM and NRC, 2014). Indeed, young adults are significantly more educated now compared with previous generations, with twice as many adults ages 18 to 31 having attained some education beyond high school in 2012 than in 1968 (Fry, 2014). However, while 85 percent of young adults enroll in college within 1 year of their 18th birthday, a majority of these young adults have not completed their degrees before age 25 (IOM and NRC, 2014). Young adults who do complete college often continue their education in graduate or professional school (Arnett, 2000). Finally, in terms of family formation, by age 25 nearly half of all young adults report having cohabitated with a romantic partner, roughly one-third have become a parent, and more than a quarter have married, with nearly two-thirds of young adults having engaged in at least one of these family formation transitions (IOM and NRC, 2014). These demographic changes and instabilities are likely to play a role in young adults’ initiation with tobacco.

Young adulthood is also an intense time of personal change and growth, which occur as the young adult is less subject to parental and societal restrictions, while simultaneously not being bound by the restrictions and responsibilities that typically characterize adulthood. Given that delay in assuming adult roles and responsibilities, the young adult period is ripe for exploration and experimentation. Young adult exploration is not so much to prepare for adult roles, but for the sake of exploration itself; it is a time of exploration prior to settling into adult roles and responsibilities. This is a time with very little expectation for marriage, parenthood, or permanent

employment, coupled with few, if any, parental restrictions, which creates a near-perfect atmosphere for identity development (Arnett, 2000, 2004). Furthermore, as young adults explore new living situations, including being away from parental restrictions and opportunities for cohabitation, and also affiliate more with peers who use tobacco, it stands to reason that opportunities for greater substance use will emerge.

Self-reflection is an important characteristic of young adult identity exploration, and three areas of self-reflection that often occur during young adulthood may affect decisions regarding tobacco use. The first is the extent to which young adults feel as if they have reached adulthood. In addition to demographic shifts, studies show that a large number of young adults do not consider themselves to have achieved adult status, as defined by financial independence and family formation; they can be characterized as still being in the “age of feeling in-between” (Arnett, 2004; Nelson and Barry, 2005). Second, given the vast amount of exploration desired by young adults and the limited restrictions and accountability that results from work or family obligations, young adults are likely to feel less accountable and therefore less vulnerable to risks during this “age of possibilities” (Arnett, 2004). Finally, young adults’ perceptions of the extent to which their peers are using tobacco, as well as whether tobacco use is viewed as acceptable, are likely to influence patterns of tobacco use (Simons-Morton et al., 2001).

A number of important findings can be drawn from the above review:

Biological Development of Adolescents and Young Adults

Physical Development

Physical development, including the development of secondary sexual characteristics, is one of the most important and noticeable hallmarks of adolescence. The emergence of these newly developed physical features

occurs on average between the ages of 10 and 15 for both girls and boys (Susman et al., 2010), leading adolescents to begin to have more of an adult-like appearance, which then often results in their own and others’ beliefs that they can and should adopt more adult roles. However, as noted below, looking like an adult does not equate to having the cognitive, social, or emotional readiness to make adult-like decisions.

Physically maturing either earlier (the lowest 10 to 15 percent of the adolescent population) or later (the highest 10 to 15 percent of the adolescent population) is associated with an individual’s likelihood of engaging in risky behavior, including tobacco use (Cance et al., 2013; Mendle and Ferrero, 2012; Mendle et al., 2007). For males, being either an early or late maturer can have negative outcomes on psychosocial adjustment (Mendle and Ferrero, 2012) and can lead to increased substance use (Cance et al., 2013). For females, being an earlier physical maturer can result in adjustment problems and, most relevant to tobacco use, to problems with body image that can lead to eating disorders (Mendle et al., 2007). Studies have shown that girls, primarily white girls, sometimes initiate tobacco use in order to lose weight (HHS, 2012). By contrast, for females, having a later physical maturation can be protective against risky behaviors and adjustment issues, including tobacco use, as compared with males, who have more adjustment difficulty if they mature late (Crockett and Petersen, 1987; Mendle and Ferrero, 2012; Mendle et al., 2007; Siegel et al., 1999).

Neurobiological Development

Physical maturation, including brain development, occurs throughout the adolescent and young adult years. Neuroscience research provides insights that show how brain maturation affects the social and emotional development of adolescents and young adults and helps explain why they are more susceptible to using tobacco than are adults.

The majority of the recent research on adolescent and young adult brain development has found that both structural and functional changes occur during adolescence, continuing into young adulthood (e.g., Giedd, 2008; Luna et al., 2004). There are four lobes in the brain: the parietal lobe, occipital lobe, temporal lobe, and frontal lobe. The frontal lobe, the largest part of the brain, contains the prefrontal cortex, which is located in the front of the brain, behind the forehead. The prefrontal cortex is responsible for executive functioning, including cognition, thought, imagination, abstract thinking, planning, and impulse control. Brain development begins at the back and progresses to the front of the brain, with the prefrontal cortex being one of the last areas to mature (Gogtay et al., 2004; Sowell et al., 1999).

The prefrontal regions of the brain, which regulate executive function-

ing and oversee critical abilities for decision making, show gradual changes in structure and function during adolescence (Casey et al., 2000) and are not fully developed until later in young adulthood (Steinberg, 2007). As a result, self-regulatory and self-control skills are not yet fully developed. In contrast, the neural network responsible for social and emotional development matures earlier, closer to the onset of puberty, and may well drive much of adolescent decision making (Steinberg, 2007). This imbalance between impulsive and reflective neural systems is normal in adolescents (Steinberg, 2007).

Throughout childhood and early adolescence, the brain undergoes synaptic overproduction, in which connections between neurons proliferate in the brain. Since this leads to more neural connections than can survive, the brain then undergoes a selective synaptic “pruning” process in adolescence into young adulthood, in which unused synapses are selectively eliminated. The synapses that survive this pruning process become more efficient and adept at transmitting information between neurons. For the prefrontal regions of the brain, which is responsible for individuals’ ability to think, this pruning process results in greater cognitive abilities (Casey et al., 2008; Giedd, 2008; IOM and NRC, 2011; Johnson et al., 2009; Weinberger et al., 2005).

At around the same time, a process of myelination occurs, whereby the amount of white matter—the part of the brain that modulates the signals between nerves—increases in the prefrontal cortex. In this myelination process, nerve fibers become coated or sheathed in myelin, a white fatty substance. Myelin accelerates the velocity at which signals travel along nerves, making nerve-to-nerve communication faster and more efficient. This process continues until young adulthood and results in more efficient neural connections, which in turn results in improvements in higher-order cognitive functioning, planning, understanding of positive and negative consequences, and decision making.

During adolescence and through young adulthood, there is also an increase in the number of dopamine transmitters in the brain. These receptors connect to the limbic system, which is the part of the brain most responsible for emotions, rewards, and punishment. This increase in dopamine receptors during this period results in an increased desire for rewards and increased sensation seeking in order to feed these desires for reward (Counotte et al., 2011).

Finally, during adolescence and into young adulthood, more and more efficient connections develop between the prefrontal cortex and the limbic system. With greater connectivity, there is more likelihood of self-regulation and impulse control. During adolescence, there is less communication among the various centers of the brain and, hence, less likelihood to control impulses associated with rewards (Steinberg, 2013).

These processes of neurodevelopment have been shown to continue through the mid-20s, with large individual differences in the rate and amount of brain maturation over time. As such, the portions of the brain believed to be most responsible for decision making, impulse control, peer susceptibility, and other aspects of psychosocial maturity are not fully developed until young adulthood, with males developing more slowly than females (Casey et al., 2008; Giedd, 2008; Luna et al., 2004).

Research on the brain helps explain why adolescents and young adults are more likely to act impulsively and to make emotionally based decisions. This pattern is due in part to the fact that the amygdala—a part of the limbic system—rather than the prefrontal cortex is used in many decision tasks during adolescence and young adulthood (Smith et al., 2013; Steinberg, 2007). Brain imaging research shows that the prefrontal cortex, which controls self-regulation, impulse control, and sensation seeking, is less mature and less effectively used in adolescents than in adults (Casey et al., 2008; Luna et al., 2010; Smith et al., 2013). Of particular importance is that the limbic and paralimbic areas of the brain (amygdala, orbitofrontal cortex, medial prefrontal cortex, superior temporal sulcus, and ventral striatum) are developing during adolescence. Given that the areas of the brain particularly responsible for processing social and emotional information and reward pathways develop earlier, it stands to reason that adolescents are particularly focused on engaging in activities for which they receive rewards and acceptance from their peers and others (Smith et al., 2013). This reward seeking and focus on peer acceptance is responsible in part for greater risk taking during adolescence. Using functional magnetic resonance imaging (fMRI), Chein and colleagues (2011) examined activity within the brains of adolescents (14 to 18 years old), young adults (19 to 22 years old) and adults (24 to 29 years old) to determine which parts of the brain are more active when an individual is making simple driving decisions that are observed by peers. The researchers found that, compared to adults, adolescents used those areas of the brain most responsible for cognitive control less. Furthermore, there was more activation in the reward areas of the brain among adolescents than among adults.

As adolescents age into young adulthood, the part of the brain used to make decisions and understand information changes, with gradual improvements and shifts to the brain areas more responsible for higher-level cognitive control. Furthermore, the ability to process information and to do so without or with limited influence from others and with little emotional influences is not fully developed until the mid-20s (Giedd, 2008; Luna et al., 2004).

Implications of Tobacco Use for the Neurobiology of the Adolescent and Young Adult Brain

The developing adolescent brain is vulnerable to tobacco use not only because of its biological immaturity but also because some of the brain areas that are critical to the emergence of nicotine dependence may not be fully developed until late adolescence or young adulthood. The ongoing changes in both brain structure and function are likely to heighten an adolescent’s vulnerability to tobacco use. The neurobiological stages and changes characteristic of adolescence, as described above, may translate directly into challenges adolescents will have in competently planning and executing the complex array of coping skills that are needed to resist prompts to use tobacco. Although most logical reasoning abilities are developed by age 16 (Steinberg et al., 2009a), the fact that some psychosocial capacities of adolescents are still immature, including delay of gratification, impulse control, emotional regulation, and the ability to resist social influences, may undermine the plans and efforts needed to resist tobacco use in the presence of cues to use. Steinberg (2007) suggests that when adolescents are emotionally aroused, their cognitive control mechanisms are further compromised.

Casey and Jones (2010) outlined how the imbalance in adolescents’ developing neurobiological systems makes them particularly susceptible to the motivational properties of substances. Smoking-specific models of adolescent smoking initiation and brain development (Lydon et al., 2014) show that the adolescent developmental period is particularly critical with regards to smoking initiation. Nicotine exposure also affects the adolescent brain differently than the adult brain. Individuals exposed to nicotine during adolescence are more likely to experience the symptoms of a protracted abstinence syndrome than are individuals exposed to nicotine only in adulthood; thus, adolescents who use tobacco products are more at risk for continuation and relapse than individuals who started to use tobacco products in adulthood (Lydon et al., 2014).

In addition to the imbalance in the maturational stages of different brain regions, the adolescent brain may be especially primed to be receptive to the rewarding effects of nicotine. Adolescent brain development is characterized by a dynamic combination of changes, including increased innervations of fibers with modulatory neurotransmitters, synaptic pruning, increased myelination of higher-order associative areas (notably the prefrontal cortex), and adaptations of various receptor levels (Counotte et al., 2011). The levels of different receptor types follow a pattern of peaking in adolescence and then declining to adult levels; thus, adolescent brains may be especially sensitive to the effects of nicotine. Some of the receptor level changes that occur during adolescence include those that play important roles in modulating the circuitry of the prefrontal cortex and in mediating

nicotine reward signals (e.g., glutamate receptors, dopamine, and nicotinic acetylcholine receptors). Adolescents also have greater brain reactivity to rewards in general than do young adults, which may also be related to novelty seeking such as tobacco use (Chein et al., 2011).

Most of the evidence about the vulnerability of the adolescent brain to nicotine comes from animal studies because of the ethical challenges of conducting this type of research in humans. Substantial evidence from these animal studies suggests that the adolescent brain has heightened sensitivity to the reinforcing effects of nicotine compared to the adult brain (Jamner et al., 2003; Slotkin, 2002), as demonstrated by both conditioned place preference paradigms and self-administration of nicotine (Belluzzi et al., 2004; Chen et al., 2008; Shram et al., 2006; Torres et al., 2008). While both animal and human studies indicate that adolescents experience fewer nicotine withdrawal symptoms than adults (Counotte et al., 2011), studies show that the reinforcing effects of nicotine are greater in adolescent rats than in adult rats, and additives to cigarettes, such as acetaldehyde, may also enhance the rate of the self-administration of nicotine in adolescent but not adult rats (Belluzzi et al., 2004). Animal models also suggest that exposure to nicotine during adolescence may increase the potential for dependence in adulthood, as adolescent rats exposed to nicotine increase their intravenous self-administration of nicotine when they reach adulthood (Adriani et al., 2003). In contrast, when rats are exposed to nicotine only after adolescence, the rewarding properties are reduced in conditioned place preference paradigms (Adriani et al., 2006).

The c-Fos gene is a marker of neuronal activation during brain development whose expression in response to nicotine is known to vary with age, with discrete periods of sensitivity in adolescence. The cingulate cortex, which is important for attention, and the retrosplenial cortex, which is activated by emotionally salient stimuli, show increased nicotine c-Fos mRNA in adolescence than in adulthood (Goldstein and Volkow, 2002; Jamner et al., 2003). These brain areas are connected with the primary visual cortex, where visual stimuli are processed initially. The visual cortex c-Fos mRNA is activated by nicotine in adolescence but is not similarly activated in adult brains, suggesting that even occasional tobacco use during adolescence may prime receptivity to the visual cues in tobacco advertising (Jamner et al., 2003).

Both the cingulate cortex and the retrosplenial cortex also influence areas of the amygdala, which are important in regulating attention, memory, and emotional response to sensory stimuli (Jamner et al., 2003; Swanson and Petrovich, 1998). Even low doses of nicotine in adolescence cause increases in c-Fos mRNA in the medial extended amygdala. This pathway also is critical to regulation of two other areas, the shell of the nucleus acumbens and the paraventricular nucleus of the hypothalamus, which reg-

ulate pathways for endocrine and behavioral outputs (Jamner et al., 2003; Swanson, 2000). c-Fos mRNA expression in the paraventricular nucleus is extremely sensitive to nicotine in the adolescent brain, and only during late adolescence (not adulthood) does nicotine-induced c-Fos expression appear in the shell of the nucleus acumbens.

In short, there are multiple brain regions that are highly activated during adolescence, and these regions form interconnected circuits that are critical to attention and motivational behavior. It is worth noting that brain development varies by sex, and these developmental differences may provide clues to differential rates of tobacco use seen in adolescent boys and girls. For example, in both animal and human studies, males are often more responsive to the rewarding effects of nicotine than are females (Donny et al., 2000; Perkins et al., 1999). There may also be sex differences in the effects of nicotine withdrawal. In animal models, nicotine administration in adolescents produces changes in brain circuitry, cell damage, and loss related to learning and memory, but these effects may be greater in the female hippocampus than in the male (Slotkin, 2002). To date, however, it has proved difficult to determine whether sex differences in patterns of brain development influence differences in the developmental trajectories of tobacco use.

In sum, brain development continues beyond adolescence into young adulthood. Individuals continue to undergo normal neurobiological changes, including developmental transformation of the prefrontal cortex and limbic brain regions, and myelination of the intracortical and mesolimbic dopamine systems continues (Benes, 1989; Thompson and Nelson, 2001). These patterns reflect growing executive function control, improved decision making, and decreases in behavioral impulsivity (Casey and Jones, 2010; Smith et al., 2013; Steinberg, 2004, 2013). The reward centers of the brain are most activated during adolescence (Chein et al., 2011; Steinberg, 2013).

The literature implies critical findings concerning adolescent and young adult brain development and its application to tobacco use. Most germane to this report are the following findings:

TOBACCO-RELATED DECISION MAKING BY ADOLESCENTS AND YOUNG ADULTS

Traditional models of decision making—for example, the Theory of Reasoned Action (see Fishbein, 1979), the Theory of Planned Behavior (Ajzen, 1985), and the Health Belief Model (Rosenstock, 1974)—describe decision making as taking place through a deliberate, analytic process; a process that involves many of the cognitive abilities discussed previously. According to these theories, decisions are based on cognitive processes that involve: (1) an assessment of the potential positive and negative outcomes associated with the behavior in question; (2) an assessment of the likelihood of experiencing personal harm from engaging in the behavior, including the likelihood that each positive (benefit) and negative (risk) outcome can and would occur; (3) consideration of one’s desire to engage in the behavior, given the potential positive and negative consequences; (4) perceptions of the extent to which similar others are engaging in the behavior; (5) perceptions of the extent to which others would accept or not accept engagement in the behavior; and (6) intention to engage in the behavior.

The understanding that adolescent cognitive abilities are largely forged by about age 16 while psychosocial maturation is still continuing has led to the development of new decision-making models that include both cognitive and noncognitive components. These dual-process models are especially relevant to tobacco use, which involves a deliberate decision process in a developmental context strongly affected by psychosocial influences that adolescents are not always equipped to process.

The dual-process models include, first, the cognitive path involving the more traditional, deliberate, reasoned, and informed aspects of the decision process. In this path, decisions rely on cognitive skills such as weighing risks and benefits and social norms, and these attitudes are expected to predict intentions and ultimately behavior. This is the path sometimes used by adolescents when making decisions that are less emotional, and it is the path most often used by adults.

The second path, which is used more often by adolescents during emotional decisions such as whether to use tobacco, involves the noncognitive aspects of decision making, such as impulsiveness, sensation seeking, and reward seeking. The influence of this path is rooted in the asynchrony observed in the adolescent and young adult brain structure and function. This path involves the more hypersensitive affective system, which leads to decisions that are more affectively based and influenced by psychosocial fac-

tors, such as peers, lower impulse control, increased sensation seeking, and self-regulation (Smith et al., 2013), particularly in an emotionally charged situation such as develops when an adolescent is faced with the dilemma of whether or not to use tobacco.

Given these two paths to decision making, it is evident that adolescents and, in some cases, young adults are strongly susceptible to developmentally grounded social and emotional influences in making decisions concerning tobacco use. Delaying the socially sanctioned opportunity for this decision, and strengthening the social disincentives to use tobacco, can reasonably be expected to reduce the likelihood that adolescents and young adults will affiliate with peers who are using tobacco and reduce the chances that they will be induced or pressured to use tobacco while their brains continue to mature.

TOBACCO INDUSTRY TARGETING ADOLESCENTS AND YOUNG ADULTS

Tobacco industry influence is an important environmental factor that increases adolescents’ and young adults’ susceptibility to using tobacco use. Tobacco companies have historically targeted children and young adults, recognizing that they needed the “youth market” to perpetuate the sales of their products (Teague, 1973). Since the 1998 Master Settlement Agreement, tobacco companies are legally prohibited from marketing to individuals younger than 18 years of age (NAAG, 1998). But while traditional cigarette advertisements are no longer allowed in broadcast television or radio, tobacco companies have responded to these restrictions by increasing their advertising and promotion at points of purchase (Feighery et al., 2001; Henriksen, 2012) and vigorously marketing to young adults via promotions at venues such as bars or events such as concerts (Ling and Glantz, 2002). The aggressive marketing of tobacco products at points of purchase and popular venues as well as the heavy exposure to images of tobacco use that individuals receive via television and movies is troubling, as studies show that adolescents and young adults may be particularly vulnerable to such marketing practices (e.g., Scull et al., 2010; Ward et al., 2006). According to recent theories of media exposure, such as the “super peer” theory (Brown et al., 2005), the media exerts a distinct influence on adolescents’ perceptions of what is normal, acceptable, and expected of them, and it

may actually exert more influence than either parents or peers (Ward et al., 2006). For example, Scull and colleagues (2010) found that adolescents’ beliefs regarding the attractiveness of advertisements for alcohol and tobacco, how realistic they felt the ads were, and how similar they felt they were to individuals in the ads predicted current use and intentions to use alcohol and tobacco over and above variables of peer and parental influence.

As described in previously secret tobacco industry documents, tobacco companies use marketing strategies to shape consumers’ and potential consumers’ perceptions of risk and to increase beliefs in the acceptability of tobacco products (Anderson, 2011). For example, the tobacco industry used terms such as “light” and “mild” to encourage tobacco use as the awareness of the health dangers of smoking grew (Etter et al., 2003; Gilpin et al., 2002; Kropp and Halpern-Felsher, 2004; Shiffman et al., 2001; Tindle et al., 2006). Similarly, a review of more than 900 tobacco industry documents revealed that menthol cigarettes were marketed as healthier than non-menthol cigarettes; such marketing was related to adolescents’ and young adults’ perceptions that menthol-flavored cigarettes were a healthier alternative (Anderson, 2011; Klausner, 2011). In addition, the tobacco industry has used aspirational visual imagery (e.g., sexy women smoking, baseball players using smokeless tobacco) to motivate tobacco use (Cortese et al., 2009; Mejia and Ling, 2010; Toll and Ling, 2005). The prominent use of the Internet and social media to market new products such as electronic nicotine delivery systems (ENDS) and smokeless tobacco further facilitates these marketing strategies and increases the tobacco companies’ reach, relevance, and opportunities to interact with young consumers, which results in perceptions of reduced risk, greater benefits, and greater social acceptability of marketed tobacco products. These messages are especially effective when the marketing messages appear to come from peers and other tobacco consumers rather than the manufacturer (Sepe et al., 2002).

Numerous longitudinal studies have found a significant relationship between exposure to cigarette marketing and subsequent smoking behavior. Hanewinkel and colleagues (2011), for example, found that adolescents with high levels of exposure to cigarette advertising were significantly more likely to smoke than adolescents who had been exposed to low levels of cigarette advertising, while exposure to other types of advertising did not affect smoking initiation rates (Hanewinkel et al., 2011). Anti-tobacco counter-marketing campaigns such as the truth^® campaign have also been shown to be successful at reducing tobacco initiation and use among adolescents and young adults (Davis et al., 2009; Emery et al., 2012; Farrelly et al., 2005, 2009; Richardson et al., 2010; Sly et al., 2001).

Point-of-sale marketing is also associated with adolescent initiation of smoking (Slater et al., 2007). In a longitudinal study showing that adolescents who frequently visit liquor stores, convenience stores, and

markets with high concentrations of point-of-sale advertising for cigarettes are significantly more likely to initiate smoking (Henriksen et al., 2010). Among young adults, it has been shown that both smokers and nonsmokers ages 18 to 30 are twice as likely to attend bars and clubs than their older counterparts, and they are also more attracted and susceptible to tobacco advertising (Biener and Albers, 2004). Ling and Glantz have also shown that marketing targeted at young adults has the consequence of promoting smoking in older teens as well (Ling and Glantz, 2002).

Influence of Seeing Smoking in the Movies

Overall, between 1950 and 1990 there was a decrease in depictions of smoking in the movies, but this was followed by a rapid increase so that by 2002 depictions of smoking were comparable in scale to what had existed in 1950 (Charlesworth and Glantz, 2005). This trend has continued, and between 2011 and 2012 there was a 45 percent increase in the number of tobacco incidents displayed per movie (Glantz et al., 2013). Exposure to smoking images in movies as well as in other sources such as newspapers and television has been found to be associated with positive assessments related to the social acceptability of smoking, smoking as a means of stress and emotional control (Watson et al., 2003), and assessments of smoking being “sexy” and “stylish” (McCool et al., 2004). Experimental studies and cross-sectional surveys have found a relationship between exposure to smoking images in the movies and smoking initiation, and longitudinal studies have found that adolescents with higher exposure to smoking in the movies were more likely to initiate smoking than peers who reported low levels of exposure (Dal Cin et al., 2012).

The tobacco industry’s efforts to manipulate tobacco-related perceptions and acceptability are more concerning as new tobacco products come to market (Ganz et al., 2015; Grana and Ling, 2014; Kornfield et al., 2015; Pokhrel et al., 2015). The tobacco industry has continued to market tobacco products aggressively. The impact of this marketing will depend on Food and Drug Administration regulation of marketing and promotional materials.

IMPLICATIONS

It is clear that the juxtaposition of numerous risk factors during the adolescent and young adult years is likely to increase the probability that first trials of tobacco use will turn into persistent use. These factors include the sequence of neurodevelopment in the adolescent years, the unique sensitivity of the adolescent brain to the rewarding properties of nicotine, the early development of symptoms of dependence in an adolescent’s smoking experience (well before reaching the 100-cigarette lifetime threshold), and

the difficulties that adolescents have in stopping smoking. Delaying the onset of any tobacco use beyond adolescence will likely decrease the probability that early trials of tobacco will be experienced as rewarding and to increase an individual’s ability to discontinue tobacco use after initial trials.

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