Galvan, A., Hare, T. A., Parra, C. E., Penn, J., Voss, H., Glover, G., & Casey, B. J. (2006). Earlier development of the accumbens relative to orbitofrontal cortex might underlie risk-taking behavior in adolescents. Journal of Neuroscience, 26(25), 6885-6892.
Goal: To examine the differences in the developmental trajectories of the nucleus accumbens (NAcc) and orbital frontal cortex (OFC) from childhood through adulthood
Methods: 16 children (7-11 years), 13 adolescents (13-17 years), and 12 adults (23-29 years) played a delayed response two-choice task while undergoing fMRI. In this task, primate stimuli were associated with specific reward amounts (small, medium, and large values without specific monetary amounts assigned so participants could not keep track during the course of the task run). During the cue period, a pirate would present on either the left or the right side of the screen. During the response period, the participant would indicate if the pirate presented on the left or the right side of the screen with a button press. Then finally, the reward would present on the screen.
fMRI Results:
- The NAcc showed increased activity for greater reward values (high > med > low) but the OFC did not.
- Adolescents showed a greater magnitude of activity in the NAcc compared to both children and adults. While, children showed greater magnitude of activity in the OFC compared to both adolescents and adults.
- Children showed a greater volume of activity (number of interpolated voxels) in the NAcc compared to children and adults. Adolescents and adults did not significantly differ in NAcc activity volume. Additionally, children showed the greatest volume of activity in the OFC. While, adolescents showed significantly less than children but significantly more activity volume than adults.
- For late trials in each task run, adolescents showed exaggerated changes in NAcc activity for small and large reward trials 5-6 seconds after the executed response button press. For small rewards, adolescents showed decreased activity compared to the other groups. For the large rewards, adolescents showed increased activity compared to the other groups.
Behavioral Results:
- For all groups, mean reaction times were fastest during the high reward trials.
- During late trials, adults had significantly faster rts during large > medium > small reward trials.
- During late trials, adolescents had significantly faster rts during large compared to small or medium reward trials.
- Children did not differ in mean rt with regard to reward size.
Discussion: Overall, these results support the idea of different developmental trajectories of NAcc and OFC recruitment which may underlie risky decision making behaviors during adolescence. The authors suggest that the NAcc may develop faster than the OFC, such that greater sensitivity to rewards during adolescence is coupled with immature prefrontal control abilities. This is one of the first studies to show that brain activity in response to rewards is related to behavioral performance.
Thoughts:
- This paper is one of the earliest to characterize developmental differences in reward and control activity. I should look into papers that have cited this one for studies that include additional regions (beyond the NAcc and the OFC) to my network hypotheses for my motivation x cognitive control first year project.
- This study is consistent with other literature reporting that reward improves rt but not accuracy across age groups.
- The task used in this study seems really simple and I wonder if we might see differences in regional recruitment with a more difficult task. Additionally, considering other reports that monetary values are not as salient for children, I think these results should be considered cautiously.