Rapidly accumulating evidence from neuroscience and behavioral genetics underscores the importance of early exposure to severe stressors for later health. In particular, such early stressors as physical and emotional abuse, emotional neglect, parental substance use, and exposure to violence in the household were linked to later adverse adolescent outcomes including drug use, addiction, and suicide.
In female youth, experience of sexual abuse was highly related to exposure to other sources of stress and was linked to earlier age at first intercourse, and unintended pregnancy. In general, the more ACEs experienced, the greater the emergence of risky behavior in adolescence and later life.
Research on primates and rodents provides some understanding of how early adverse experiences can produce long-term effects on behavior that can emerge in adolescence. The research of Meaney and colleagues with rats indicates that variation in early maternal care can produce epigenetic effects on offspring. In the rat, mothers who are less nurturing in their care of newborns are more likely to produce these effects. These effects appear to be mediated in part by reduced levels of serotonin functioning in the hippocampus.
There also appear to be adverse effects on spatial ability and memory mediated by hippocampal functioning. This also leads to less than optimal responses to stressful experiences in offspring Meaney, The perhaps most remarkable consequence of these epigenetic processes is that female offspring of less nurturant mothers are more likely to behave in a similar manner with their offspring.
Using cross-fostering designs, it is possible to determine that this results from intergenerational transmission of experience rather than genes. That is, it is the experience of maternal behavior that produces the effect rather than genetic transmission from parent to offspring.
Early experience in primates produces similar effects. Suomi's research with rhesus monkeys that are either reared by their mothers or by much less nurturant peers finds that peer-reared males exhibit greater externalizing behavior in adolescence Suomi, In research with rhesus macaque monkeys, Maestripieri and colleagues have examined neurobehavioral effects of maternal abuse and neglect on offspring Maestripieri, They also find that maternal maltreatment is transmitted by behavior rather than genetics.
In addition, they find a particular role for serontonergic mediation that appears to increase impulsivity in offspring. One interesting aspect of this research is that the short allele of the serotonin transporter gene enhances the effects of maternal abuse, a finding consistent with research in humans who experience abuse during childhood Caspi, Sugden, Moffitt, Taylor, Craig, Harrington, et al.
Research with humans also suggests that early maltreatment by parents is associated with later conduct problems. In a longitudinal study of high risk children from ages 2 to 8 Kotch et al. Later neglect did not predict aggressive behavior at this early age. One difficulty in testing the epigenetic explanation for increased HPA axis reactivity in humans is the need to examine brain tissue. In a recent study, McGowan and colleagues examined hippocampal tissue in deceased persons who committed suicide or died by other means.
In addition, those who died by suicide were distinguished as to whether they had experienced abuse or neglect as children or not. According to the epigenetic explanation, persons who suffered child maltreatment should have exhibited greater evidence of gene silencing in regions related to the stress response, including the hippocampus. Their study indeed identified such effects, thus providing the first evidence of similar epigenetic effects in humans.
Meaney's research suggests that maternal behavior toward offspring is a function of the stress experienced by the mother. Mothers who experience heightened stress treat their newborns with less nurturance, a process that is attributed to a defensive reaction to the environment. Although this may confer some advantage to offspring in the form of increased impulsivity, it can be a detrimental characteristic in humans especially when it results in conduct disorder and other externalizing conditions that increase risk for injury and incarceration.
Studies of risk behavior trajectories during childhood and adolescence indicate that in addition to an early onset trajectory that persists throughout adolescence, there are often one or more trajectories that develop during adolescence and late adulthood. Moffitt referred to these as adolescent-limited trajectories because they tend to decline as youth enter adulthood. One of the largest sources of these trajectories is a rise in sensation seeking that appears to characterize a majority of youth during the adolescent period.
The rise in sensation seeking is linked to an increase in the release of dopamine to the ventral striatum Chambers et al. Spear has identified this as a biological universal in mammals that appears to encourage the adolescent animal to leave the family and to venture forth with peers to explore new territory and select mates.
The overall level of sensation seeking is greater in males than in females, and males exhibit a prolonged period of change in this trait. Whereas female youth peak around age 16, male youth do not reach their peak until about age This rise in sensation seeking is one manifestation of dopaminergic activation of the nucleus accumbens, a process that peaks during adolescence. Furthermore, individual differences in this trait have been linked to a host of risky behavior tendencies in both adolescents and adults Roberti, ; Zuckerman, Longitudinal trends in use of alcohol, marijuana, and cigarettes as reported in the Monitoring the Future Study.
One important question related to the rise in sensation seeking during adolescence is whether it is associated with a lack of executive control over behavior as the other forms of impulsivity manifest. Evidence is sparse on this question, but given the small but significant positive correlation between sensation seeking and IQ Zuckerman, , it would seem that persons who exhibit stronger sensation seeking drives are no less able to exert executive control over their behavior.
Thus, it seems that one of the more powerful sources of risk taking in adolescence is not associated with deficits in executive function. They found spatial and long-term memory deficits in anti-social youth that are consistent with deficient hyppocampal function brought on by childhood abuse.
However, youth who merely exhibited a small rise in anti-social behavior during adolescence were no different from non-offending youth on most measures of cognitive function.
Given the powerful role of sensation seeking in adolescent risk taking, it is of interest to determine whether its effects on decision-making involve different processes from those that are used by adults. In a recently proposed model of adolescent risk taking, Romer and Hennessy suggested that the influence of sensation seeking is mediated by the same processes that underlie adult decision making, namely the use of affect as the basis for evaluating behavioral alternatives.
Furthermore, use of the heuristic introduces a reciprocal relation between perceptions of risk and reward. That is, the more favorable the affect attached to an option, the less risk is associated with it. The inverse relation between risk and reward is a deviation from rational choice models of decision-making in which risks and rewards are evaluated independently.
Indeed, risks and rewards are generally not correlated in the world of uncertain consequences Slovic et al. However, it appears to be a characteristic of our decision making to impose an inverse relation between these two dimensions of choice. This decision calculus makes us subject to certain biases of judgment controlled by dominant affective reactions to behavioral options. Those activities we enjoy tend to be seen as less risky than those that are actually safer but less affectively pleasant.
Hence, we prefer to drive cars rather than take trains even though, all else constant, trains are far safer than cars. Nevertheless, the heuristic renders decision making simpler than a careful consideration of both risks and rewards would require. From the perspective of developmental neuroscience, the use of the affect heuristic is an interesting phenomenon. Because it requires very little deliberation, it can guide behavior without the need for extensive cognitive control.
As a result, there is little reason to believe that it should depend on extensive maturation of cognitive control mechanisms during adolescence. Not surprisingly, when we examine the risk taking behavior of adolescents, we find that the affect heuristic is alive and well in this decision making realm.
For example, in evaluating the affect attached to smoking, drinking alcohol, and smoking marijuana, judgments of favorable affect and risk are strongly inversely related to each other and form one factor that is strongly related to use of each drug.
Indeed, risk judgments add no significant prediction of drug use beyond the positive affect attached to each drug. Another important characteristic of adolescent risk taking is the influence of peers. As seen in Figure 6 , sensation seekers not only attach favorable affect to novel and exciting experiences, they also seek out peers who have the same interests. This selection process creates a social environment that not only encourages risk taking, but that also enhances the favorable affect that is attached to novel experiences.
Because youth who differ in sensation seeking essentially congregate with similar peers, the effects of their own sensation seeking levels are reinforced by exposure to others through a process of affect transfer. Given that youth of a similar age simultaneously experience the same rise in sensation seeking, this peer effect magnifies the affective attraction to novel and exciting behavior such as drug use.
As a result, the effects of affect on behavior are enhanced by peer influences. As seen in Figure 6 , the path weights linking the factors in the model suggest that both sensation seeking and peer influence converge on affect evaluation and produce more change in behavior through this path than through peer influence alone.
In total, affect evaluation and peer influences account for over half of the variation in the use tobacco, alcohol, and marijuana. This influence in not limited to effects on drugs. In a study of failure to use seat belts when adolescents travel in cars, Dunlop and Romer found that about half of the variation in this behavior was related to affect evaluation and peer influence.
In that case however, the influence of peers was somewhat stronger than affect alone. Our findings regarding the effects of sensation seeking on adolescent risk taking suggest that it is possible to explain a great deal of the rise in risky behavior during adolescence to the increase in this form of impulsivity. Furthermore, the decision processes that are influenced by sensation seeking are the same as those that are used by adults. Indeed, the affect heuristic requires little deliberation and would appear to be available for use by the beginning of adolescence if not earlier.
Finally, sensation seeking does not appear to reflect a deficit in executive functioning as is the case with other forms of impulsivity. Thus, there is little evidence to suggest that the risk taking associated with sensation seeking reflects a deficit in PFC brain maturation. The evidence we have reviewed suggests that adolescent risk taking is not a universal phenomenon and that individual differences related to at least three types of impulsivity underlie such behavior in adolescents.
Furthermore, at least two forms of impulsivity are associated with weak executive function as assessed by working memory and response inhibition tasks. However, sensation seeking does not appear to be inversely related to either of these executive functions and may actually be somewhat positively related to working memory ability.
Could these maturational changes reflect alterations in brain structure that place limits on adolescent cognitive control over risk taking? There is virtually no direct evidence to support a relation between natural maturation in brain structure during adolescence and impulsive behavior. This is partly due to the fact that it is difficult to observe changes in brain structure that could be implicated in impulsive behavior.
As noted by Galvan et al. Neuroimaging studies cannot definitively characterize the mechanism of such developmental change e.
However, these volume and structural changes may reflect refinement and fine-tuning of reciprocal projections from these brain regions PFC and striatum during maturation. Thus, this interpretation is only speculative. Lu and Sowell reviewed what is known about the relation between changes in brain structure during development and performance on cognitive and motor skills.
Their summary does not provide much evidence for the hypothesis that cortical thinning reflective of synaptic pruning leads to improved cognitive performance. For example, holding IQ constant, Sowell and colleagues found that cortical thinning from ages 5 to 11 was associated with greater improvement in vocabulary, an effect that would seem to be driven by learning rather than brain maturation.
In a study examining changes in cortical thickness from ages 7 to 19 as a function of different levels of IQ, Shaw and colleagues found that individuals with superior IQ began the thinning process later than those with normal IQ. If cortical thinning facilitates the development of cognitive skills, then one would expect it to occur earlier for those with higher IQ.
Hence, cortical thinning does not even characterize skill development across all regions of the cortex. Holding constant age, they found that risk taking tendencies were positively correlated with white matter development.
Consistent with this finding, DeBellis and colleagues found that myelination of the corpus callosum was more advanced in youth with alcohol disorders than in control youth without such conditions. Thus, evidence in support of delay in PFC myelination as a risk factor for problem behavior in youth is not only absent but also contrary to what would be expected. In summarizing this research, Lu and Sowell noted that:.
Correlations between morphological and skill maturation, although instructive, reveal only associations and cannot elucidate causality. Neuroscience must still rely on animal studies using controlled experimental designs to learn whether morphological maturation enables the acquisition of skills or if skill acquisition drives morphological change.
Some researchers have attempted to observe differences in brain function while engaging in risky decision-making that could help to identify age-related differences in brain development. These studies have used functional magnetic imaging fMRI of individuals varying in age from childhood to adulthood while engaging in a variety of tasks. While some of these acts are relatively harmless, others — swilling a few beers at a party or cliff-jumping into a lake at night — can be downright dangerous.
Parents of teenagers often find themselves scratching their heads and wondering what on Earth their kids were thinking. For one, adolescence is a critical period of neurological development that can explain a lot of behaviors that, to parents, may seem inexplicable. The truth is, massive developmental changes occur at this time and require parenting skills to help.
Most notably, by better understanding the biological aspects of teenage brain development, parents can not only improve their empathy, but also facilitate safe and moderately structured environments to assist them with the multitude of competing priorities emanating from their environment.
It takes a high-functioning brain to understand that something that would be really fun in the moment could have consequences down the road. When necessary, parents also need to offer hard guidance away from clear and present dangers — like drugs and alcohol. Along with talking with your teen about the real brain dangers, you can support their development just by being there: being present, patient, and understanding.
It takes an environment that is stable, caring, empathic, and tolerant. Good news: These reward-seeking impulses can be harnessed for good. Teens will disproportionately value being awarded, say, an extra hour of television time than they will course-correct from losing an hour of television time.
When it comes to behaviors or activities you feel strongly about, set clear boundaries. Let your teen know these actions are not acceptable. It also conveys to your teen that he can have independence in n-number of other areas, making him more likely to try to abide by the limitations that really matter to you.
Fortunately, and maybe surprisingly, teens can be extremely good at making sound, reasonable decisions.
Researchers found teens were able to perform just as well on the driving tests as adults in the cool environment — but when emotions were high, teens performed significantly worse, breaking stop signs and getting into accidents. This is because emotional situations activate the more mature limbic system and suppress the still-developing PFC.
So, help your teen become aware of their emotional states and identify when environments and feelings could be clouding their decision-making; for example, you might tell your teen to ask themselves if they feel comfortable or uncomfortable in any given situation. Providing them with a framework to evaluate themselves and their surroundings will help your teen make more reasonable decisions — even when they are away from you. She also loves a good run, a solid yoga pose, and the Radiolab podcast.
Follow us. Newsletter Exclusive news delivered to your inbox. Nov 2, Share. In the light of these future consequences, attending practice might not look so bad after all.
Yet, research shows that teenagers, more often than people of any other age, tend to follow their short-term impulses rather than pursuing long-term goals. Why do teenagers have so much difficulty controlling their impulses?
And how does this get better as you get older? We studied the developing brain and found that controlling impulses depends on at least two different brain areas. As you grow older, connections between these two brain areas get stronger: this helps you think about the future consequences of your actions, be less impulsive, and maybe also make better decisions.
In your teenage years, your parents usually start to allow you to make more and more decisions yourself. You start picking hobbies, the friends you hang out with, and what to do after school. Then, at some point, you become independent from your parents [ 1 ].
This growing-up phase is called adolescence. It starts with puberty and ends whenever we consider someone an adult spanning ages 10—20 years, roughly. It is a very special phase because adolescents behave differently than younger kids and adults in many ways. For instance, teenagers are known for their impulsive behavior. That is, they seem to do many things without thinking too much about the consequences. In some ways, impulsivity can actually be a good thing: imagine if you only did things for which you knew the consequences exactly!
This would not only be mind-numbingly boring but also make it impossible to learn anything new. Going into a swimming pool for the first time might be scary, but then again, you cannot learn swimming without going into the water. Teenagers, but not young children, are allowed to make their own decisions and they spend less time under the direct supervision of their parents.
This gives teenagers a lot of opportunity to learn new things, but because making the right decisions is not always easy, this freedom may also lead to mistakes. Sometimes these mistakes, driven by impulsive behavior, can lead to serious negative outcomes. For instance, teenagers end up in emergency rooms after being involved in accidents more often than adults or children [ 2 ]. So, why are teenagers so impulsive? Understanding this impulsivity is important for parents who need to let their kids have their own experiences but do not want them to be involved in accidents , teenagers who want to have fun but also need to think about future consequences , and society which needs to make laws about the appropriate age requirements for risky activities, such as drinking alcohol, smoking, or driving a car.
In an effort to understand how teenagers make very impulsive or less impulsive decisions, we studied the developing brain. We investigated one particular aspect of impulsivity, namely, impatience.
0コメント