Background/context
Subjective value = the value an individual gives to a stimulus
Expected value = sum of all possible outcomes of a choice
Ontogenetic differences = differences in biological development
The adolescent reward system is hyperactive but this may confounded by differences in how teens look at money compared to adults
Barkley-levenson's 3 hypotheses
1- Adolescents will exhibit greater behavioural sensitivity to EV than adults
2- Neurobiology Vs. activation will modulate in proportion to increasing EV more for adolescents than adults
3- Adults behaving like adolescents in terms of gambling will not exhibit hyperactive striatal activation
Aim
To investigate whether adolescents attach more value to rewards than adults do
Method
Quasi-experiment with independent measures design, lab conditions.
IV= adult or adolescent.
Dv= neural activation in brain using fmri during asimple gambling game
Procedure
Sample-
19 right handed adults aged 25-30 and 22 right handed adolescents aged 13-17 recruited through adverts at UCLA
Intake session-
P's visited lab for intake session and neuroimaging, and provided informed consent
Each p asked to provide their primary money source, and amount of spending money per month
Significant difference in spending money between adolescents ($52) and adults ($467)
P's familiarised with scanner by a mock scanner, and paid $20 for the intake session, they were informed they could use it as spending money in the lab session, and informed that they could win $20 more OR lose the original $20 in the gambling fMRI task
Actual session-
A week later, p's returned for the fMRI session and completed a gambling task, then presented with a series of gambles with a 50% probability of gaining amount shown on 1 side of the spinner OR losing the amount shown on the other side
Gain and loss amounts ranged between -$20 and +$20
144 trials, 24 gain only and 24 loss only
order of the stimuli was counter balanced across p's and for each trial, p's decided whether or not to gamble that money and were informed that one of the trials they accepted would be played for with real money, this encouraged a choice on each trial that was consistent with the p's gambles
Findings
20 adolescents and 17 adults in the final sample because the others didn't produce useful data
Acceptance rates didn't change in either group when there was no risk involved in the trials, suggesting adolescents behave similarly to adults when there is no risk involved
Across all p's all trials will positive EV's accepted more than ones with negative EV
No significant difference between groups in % of EV + trials accepted, % of EV0 trials accepted and % of EV trials accepted
Increased EV = increased likelihood of an acceptance response and even more activation in the VS in adolescents than adults, as EV increased
Amount of disposable income didn't have a effect on relationship between EV and acceptance rates
no significant differences between groups' reaction time
Increasing EV had a stronger influence over gambling choices in adolescents
Activation in some brain areas increased with increasing EV, while activation in other brain areas decreased with increasing EV
Conclusion
Value of available options = greater influence in adolescents, even with constant observation and sub values
Maturational changes in neural representation of valuation during adolescence = more robust in the Ventral striatum
Neural differences in sensitivity to EV change across development
Hyper-activation of reward circuitry in adolescence = normative ontogenetic shift = adolescents do more risk taking behaviour
Evaluation
Risk that p's may drop out of study because it was longitudinal, but it was ethically sound and FMRI can cause discomfort and claustraphobia
Adolescents may fall under social desirability effects
Small sample size and lacked ecological validity