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American College of Pediatricians - March 2011
ABSTRACT: Can sexual activity, alcohol and drug use, and other risky behaviors damage adolescent minds? In a word – yes. Early high-risk behaviors, including sexual encounters, are powerful influences and appear to be harmful to the brain’s development. The hormones and neural patterns triggered can lead to addictive, high-risk behaviors, social withdrawal, and depression. What’s more, these adolescent behaviors may have additional long-term negative consequences – not just for them, but also for their future children.
Shakespeare wrote, “I would there were no age between ten and three and twenty… For there is nothing in the between but getting wenches with child, wronging the ancientry, stealing, fighting.” (The Winter’s Tale, Act III, Sc. iii) It is amazing that over 400 years later, scientists are confirming Shakespeare’s observation that the adolescent’s brain is not fully mature until approximately 23 – 25 years of age. New and ongoing scientific research, utilizing functional magnetic resonance imaging (f MRI), demonstrates that during adolescence nearly every aspect of the brain is undergoing dramatic changes--changes that are not just genetically determined, but are greatly affected by experiences and environment. The “nature versus nurture” debate is no longer relevant, as this research clearly documents that both have impressive impact. Environment affects the growth and development of brain cells, impacts the wiring of these cells, and affects which cells live or die. More importantly, it is possible for changes engendered by the environment to be passed genetically to the next generation by “epigenesis,” the ability of cells to turn geneson and off in response to the environmental influences experienced by those cells.1 Thus, activities and experiences impact the development and functioning of the brain, not just during the adolescent years, but for the long term, with implications for future generations.
Between 11 and 13 years of age, the adolescent’s brain experiences rapid growth of nerve cells, along with increased numbers of connections between nerves (synapses). Since the adolescent brain is undergoing rapid development, this is a time of great vulnerability. This growth is followed by a time of “pruning,” when nerve cells that are not used or needed are deprived of nutrition and die. The pruning process allows the adolescent brain to function more rapidly for tasks that are already known, but decreases the brain’s capacity to learn new tasks or acquire new skills.2
Along with changes in the number of neurons, the brain also experiences changes in its hormonal environment. It has been known for decades that adolescence is characterized by surges in sex hormones--estrogen and testosterone. Recently it has been demonstrated that receptors for these hormones exist in many organs of the body, other than the brain. In addition, other hormones (neurotransmitters) such as dopamine, serotonin, oxytocin, and vasopressin also influence brain development.
Dopamine, the hormone most responsible for feelings of pleasure, has a powerful impact. The early adolescent brain, with its increased number of nerve cells, has higher levels of dopamine circulating in the prefrontal cortex, but dopamine levels in the reward center of the brain (nucleus accumbens) are decreasing. These decreasing levels of dopamine in the reward center suggest that the adolescent requires more excitement and stimulation to achieve the same level of pleasure as an adult. 3 So the teenager will attempt riskier behaviors to achieve elation. Dopamine is also the hormone secreted when individuals participate in various addictive behaviors. Drug use, gambling, video gaming, pornography, and sexual experiences can all become addicting as the individual strives to achieve a dopamine-mediated pleasure. As their brain is under construction and nerve pathways are forming, adolescents become addicted more easily.4 This vulnerability of the developing brain may well explain why these behaviors identified in adults often have their onset during adolescence or early adulthood. For example, 40% of adult alcoholics identify onset between 15 and 19 years of age.5 In addition, adolescents are more likely to become addicted with less exposure to a high-risk behavior. Although an adolescent may smoke fewer cigarettes than an adult, the adolescent demonstrates higher rates of addiction. 6
Recent research has investigated the influence genes exert on an individual’s willingness to take risks Dopamine receptor DRD4 appears to play a major role in determining the risk-taking behavior of the individual. Adolescents may be viewed as either “high risk takers” or “low risk takers” depending upon their genetic propensity to seek excitement through risky behaviors. Alcohol can affect the expression of the risk-taking gene, causing adolescents who are not generally considered “high risk takers” to take risks when under the influence of alcohol.7 Research also demonstrates that adolescents who drink alcohol are more likely to participate in other high-risk behaviors, including sexual activity. Marijuana is another drug that can affect an adolescent’s decision making, decrease inhibitions, and thereby increase risk-taking behaviors. 8 These behaviors in turn further modify the structure and function of the brain.
Oxytocin and vasopressin function as “bonding” hormones. Oxytocin, a protein secreted during labor, delivery, and breastfeeding, is also powerfully active in the female brain during physical touch or even intense gazing. Oxytocin release increases the likelihood that the female will trust her sexual partner but decreases the functioning of her frontal cortex, the judgment center. The hormone serves to bond the woman to her mate with repetitive touches and sexual relations increasing the likelihood of monogamy.9Vasopressin serves much the same role in men.
Adolescents who initiate sexual activity early are more likely to have more sexual partners by early adulthood. The Centers for Disease Control and Prevention documented that 58.1% of adolescent girls report more than five sexual partners if their sexual debut occurred younger than 16 years of age. However, if sexual debut occurred at age 20 years or older, only 15.2% had more than five sexual partners during the next five years.10 Since sexual touching brings pleasure and raises dopamine levels, the developing adolescent brain, in its craving for repetitive elevations of dopamine, overrides the healthy bonding effects of oxytocin and vasopressin. This, in turn, makes it more difficult for the adolescent to maintain a monogamous relationship later in life, as demonstrated by studies reporting that married adults who have experienced premarital sex are more likely to suffer divorce than those who abstained.11
The frontal lobe, the judgment center or CEO of the brain, allows the individual to contemplate and plan actions, to evaluate consequences of behaviors, to assess risk, and to think strategically. It is also the “inhibition center” of the brain, discouraging the individual from acting impulsively. The frontal lobe ultimately develops connections to many other areas of the brain, so that experiences and emotions are processed through the judgment center. The frontal lobe does not fully mature until approximately 23 – 25 years of age.12 The immaturity of the adolescent’s judgment center explains much of the inability of adolescents to properly interpret experiences in the environment and thus make appropriate and healthy decisions.
Many other areas of the brain likewise are not completely myelinated until the early 20s. The amygdala, which is the emotion center of the brain, is immature in adolescents and not fully connected to the frontal lobe. Adolescents, then, may have a more difficult time interpreting their emotions, as well as the emotions of others.13 The hippocampus, the memory center of the brain, is also immature and is very susceptible to the effects of alcohol. Alcohol can hinder the ability to develop memories and thereby impact learning. Adolescents who binge drink are particularly susceptible to the negative effects of alcohol on the developing hippocampus.14
Therefore, the adolescent’s brain is prone to seek excitement at a time when the frontal lobe is not mature enough to moderate such behavior. This is also the time when the developing brain is at greatest risk to form neuronal connections that may lead to addictions and impact future emotional well being and decision making. Making matters worse, modern media portrays high-risk behaviors as admirable, exciting, and even safe, while discouraging parental involvement that would positively modify the behaviors.
There is a clear link between high-risk behaviors and subsequent depression and even suicide. In the National Longitudinal Study on Adolescent Health, 13,491 adolescents in grades 7 to 1l were interviewed in 1995 and again one year later. The authors differentiated the cause and effects of depression and found that early high-risk behaviors, including sexual activity and drug use, were linked with later depression, but early depression did not cause high-risk behaviors.15
Further analysis of the same study revealed that adolescents who had involvement in any drinking, smoking, and/or sexual activity were significantly more likely to suffer from depression, suicidal ideation, and suicide attempts.”16
In summary, this evidence-based research on brain development must serve as an impetus for all adults who interact with and care for adolescents to reconsider the health information provided to youth. The adolescent brain is under construction and can be adversely affected by high-risk behaviors and by the environment the brain experiences. The judgment center is immature, leading to poor decision making. The dopamine pleasure system is in a state of rapid change, leading to higher potential for participation in high-risk behaviors and addictions. Oxytocin and vasopressin are present and ready to emotionally bond the teenager to any individual with whom he or she has sexual experiences, and heighten the consequences of the likely ending of the relationship.
Clearly, the adolescent years are a time of rapid brain development, a time of susceptibility. Those who care about the future of the adolescent must acknowledge that high-risk behaviors encountered during these vulnerable years can have lasting adverse consequences and should be avoided.
The good news is that parents play a pivotal and crucial role during the adolescent years, and the influence of parents can positively impact the developing brain. Alan Booth, a researcher at Pennsylvania State University, evaluated the role of parenting on adolescent high-risk behaviors and found that even adolescents who are more prone to them will be less likely to participate if they have a close relationship with their parents.17 Researchers at the National Center on Addiction and Substance Abuse (CASA) at Columbia University demonstrated that adolescents with ”hands-on” parents (those who monitored the activities of their adolescents and participated in family dinner hour together) are at one-fourth the risk of substance abuse as those with “'hands-off” parents.18Parents can help shape their adolescent’s environment, affect the adolescent’s tendency to participate in high-risk behaviors, and can help them in their decision-making and critical thinking skills. An adolescent’s close relationship with his/her parent is protective despite other negative environmental factors. Research clearly shows that parents play a critical role in the healthy development of their adolescents. Health care professionals should acknowledge this, encourage parents to develop healthy relationships with their children, and support them in the parenting role. On a broader level, public health policies that currently treat adolescents as young adults in their abilities to problem solve and make decisions should be re-evaluated and revised based on this new research and will need continued revision as new information emerges.
Principal author: Jane Anderson, MD, FCP
The American College of Pediatricians is a national association of licensed physicians and healthcare professionals who specialize in the care of infants, children, and adolescents. The mission of the College is to enable all children to reach their optimal physical and emotional health and well-being.
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6. Ibid.
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17. Bower B.Hormone-linked problems reflect parent-child bond - Testosterone's Family Ties. Science News. Accessed March 17, 2011 at http://findarticles.com/p/articles/mi_m1200/is_3_163/ai_96953948/.
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