by Lauren Graf, Neuroscience major, Kenyon College Class of 2020
In this blog post I have decided to discuss motivational systems, including risks and rewards, in adolescence. This post is based off of an annotated bibliography in which I looked at articles that focused on these motivational systems. The topic is one of major interest, as everyone goes through adolescence and may experience these changes in their lives.
Article 1:
Galván begins by defining adolescence as a time period during which individuals exhibit more risk-taking behavior and have heightened reward sensitivity while also developing social, physical, and cognitive skills needed for independence. She mentions how this increased risk-taking and heightened reward sensitivity may actually be beneficial in helping adolescents learn from novel experiences in order to become more independent. She then also defines reward sensitivity as increased motivation to obtain rewards and an increased response to the rewards. It is not hormones alone that are controlling these changes in adolescents, as they work together with the developing brain. Galván states the goal of the paper is to focus on how adolescent reward sensitivity is seen across species, how changes in the dopamine neurocircuitry results in heightened reward sensitivity in adolescents, and how there are individual differences in reward sensitivity and how these may be predictive of “real-world” scenarios. Even though this increased risk-seeking behavior may produce outcomes that are not ideal, it is necessary to help individuals grow and develop.
Researchers have tested rats and other non-human primates and compared their reward-related behavior to that of humans. They found that adolescent rats also demonstrate increased reward seeking, risk taking behaviors, social interactions, and an increased interest in drugs, just as in human adolescents. These results help to support evidence that there are actual changes in the brain causing these behaviors, and that it is not just cultural or social norms. Many studies have chosen to focus on changes in the dopamine system, which fires in response to rewards, social interactions, and unexpected events and stimuli. This response then leads to approach behavior, as an individual is going to want to do something more often if there is a reward involved. In adolescence, it has been shown that dopamine D1 and D2 receptors increase in the ventral striatum, while it has also been observed that the dopamine neuron firing rates and the number of activated dopamine neurons in anticipation of reward both peak in adolescence.
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| https://www.everydayhealth.com/dopamine/ |
Studies have also helped to show that adolescents have an increased sensitivity to different types of rewards. For example, it has been shown that adolescents have the greatest ventral striatum activation in response to the largest monetary reward. They became slower at responding to the smaller rewards, and quicker to react to the larger rewards. This hyperresponsive view is also supported by other work that found that adolescents had more activity in the VS when earning money, and that there is a heightened VS response to both the preparation for a reward, and the expected and unexpected reward outcomes. This has all been found to correlate with “real-world” sensitivity and task performance.
Another important topic that Galván touches on is that there are individual differences in reward sensitivity. Those who are more likely to participate in risk-taking behavior and who seek novelty are more likely to be more reward-seeking. Work by Galván has shown that those who have greater VS recruitment are more likely to exhibit risk-taking behavior more often. It has also been shown that hormones do have an impact on the dopamine system. For example, studies have shown that adolescents who have higher levels of testosterone had an increased reward-related activation in the VS. While the developing brain is an important factor in reward sensitivity, puberty does also play a role in this.
Galván concludes the paper saying that more research needs to be done determining the importance of the prefrontal cortex in this system, how other individual factors may influence behavior and risk-taking tendencies, and how this reward sensitivity affects learning. It is important for us to determine these questions and do more research on the topic in order to be better able to help adolescents at home and in schools.
Article 2:
The authors begin by describing adolescence as an important developmental time period in which individuals will exhibit increased risk taking behaviors such as experimenting with alcohol and drugs. While many of the changes that adolescents experience are adaptive and help them to become more independent, some of them may be detrimental, like excessive alcohol consumption. 32% of emergency treatments from alcohol poisoning in the Netherlands was to help adolescents 15-19 years old. This shows that excessive alcohol consumption is a major detrimental risk that many adolescents are taking. Due to this, the researchers wanted to know more about the relationship between alcohol consumption in adolescents and changes in the brain. The ventral striatum, particularly the nucleus accumbens, has been known to be associated with increased risk-taking and reward-seeking behavior in adolescence, so it was of major focus for the research group. They used fMRI information in which participants completed a gambling task from a previous longitudinal study in adolescence over two time points. Researchers also had participants fill out an alcohol consumption questionnaire that tested average alcohol consumption per evening, alcohol consumption over the past month, and total lifetime alcohol consumption. In addition, participants were also asked to provide a testosterone sample from saliva. Participants varied in age from 8 to 27 years old. The researchers hypothesized that age and alcohol use would have a positive correlation, that participants with higher reward responses in the nucleus accumbens during the gambling task would have higher alcohol use, and that higher levels of testosterone would also be seen with higher alcohol use.
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| https://bodytomy.com/structure-function-of-nucleus-accumbens |
Results showed that there is a positive correlation between nucleus accumbens activation in response to receiving a reward and the average amount of alcohol consumed per night. The study also demonstrated that testosterone levels from the first time point could help to predict alcohol use at the second time point, however, the nucleus accumbens activation at the first time point did not predict alcohol consumption at the second time point.
To conclude, the researchers state that there is a relationship between real-world risk-taking behavior and brain activation to rewards. They also mention that based on the findings that testosterone levels can be predictive of alcohol consumption in the future, it should be looked at how testosterone levels have an impact on brain development and how these combined impact real-life risk-taking.
Article 3:
The authors begin by stating that adolescence is a time of development and risk-taking. They then mention the nucleus accumbens, and how it is a crucial area of the brain involved in the brain’s reward circuitry, specifically during adolescence. However, the relationship between the nucleus accumbens activity and risk-taking is not well understood. One factor they discuss that might help explain the relationship between the two is testosterone levels. Another factor they mention is individual differences in risk-taking behaviors. This longitudinal study was designed in order to test the relationship between nucleus accumbens activity to rewards, pubertal development, and risk-taking behavior. Participants were from the age of 8 to 27, and participated in multiple tasks. There was a gambling task which involved winning or losing money, a balloon analog risk task (BART) which corresponded with real-life risk-taking behaviors, a Behavior Inhibition System/Behavior Activation System (BIS/BAS) questionnaire for self-reported risk-taking tendencies, a Pubertal Developmental Scale, and testosterone levels were measured through saliva.
Results helped to confirm that there is a peak in nucleus accumbens activation in response to rewards, which had been identified in earlier studies. This is seen to be associated with a structural change in the volume of the nucleus accumbens. Results from this study have also concluded that pubertal changes begin earlier in girls than in boys based on self-reported information, and a serious increase in testosterone is seen in boys around age 10 as compared to a moderate increase in girls. When assessing risk-taking in individuals using the BART task, there was a peak in adolescence, which was also seen in previous studies. However, when measuring risk-taking through a self-assessment, there was no change over age which could possibly be due to individual differences aside from age. Self-reported risk-taking might just show the risk taking tendency of the individual, not how it changes over time, while using the BART to measure risk-taking shows when individuals are more likely to make risky decisions. The researchers also found that individuals with higher BAS scores over time had greater increases in nucleus accumbens activity, so the differences in self-reported risk-taking correlate with activity in the nucleus accumbens. Lastly, they found that elevated nucleus accumbens responses to rewards were related to increases in puberty and higher testosterone levels.
The authors conclude by saying that future research is needed in order to determine factors that lead to a stabilized response to rewards in adulthood. Having this information may be able to help more individuals control their risk-taking tendencies and make safer decisions.
The authors conclude by saying that future research is needed in order to determine factors that lead to a stabilized response to rewards in adulthood. Having this information may be able to help more individuals control their risk-taking tendencies and make safer decisions.
References
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