Age differences in the processing of value in the human brain

Functional magnetic resonance imaging identifies different brain areas sensitive to expected values in young and older adults.

   Imagine that a vitamin that is supposed to enhance your health costs $200. Imagine further that 80% of people do not show any benefits from consuming this vitamin. Data from our recent study suggest that persons who are older, around the age of 60 years and above, are more likely to accept such stakes (i.e., pay $200 for the vitamin), despite the overall expected loss. By comparison, young adults around the age of 20 years appear able to note the negative expected value of the above economic choice and are more likely to refuse to spend money in such cases. Such age differences in value-based decision behaviors are remarkable in that both young and older adults are exposed to the same magnitude and probability information, yet they display discrepant distributions of choice responses. Indeed, it is well known that value-based decision behaviors in human processing of value are not always based on seemingly rational calculations but are influenced by subjective factors, at least in terms of financial decisions. As suggested above, one important potential contributor to subjective differences in value-based decisions is age.

   Aging is associated with changes in psychological motivations (e.g., having different goals in life) as well as altered brain biology that likely contribute to how older adults make real life decisions. However, differences in the way neural networks in young and older adult brains process value information is unclear. With population aging, the proportion of older adults making value-based decisions is increasing, especially in high-density metropolitan cities. Such a change in population demographics with accompanying changes in types of decisions made will impact healthcare and economy, at the very least. Thus, a clear understanding of how the aging brain processes value is critical to better inform policy making among other societal applications.

   In the present study, we assessed young and older adult performances in a lottery choice task (LCT; Figure 1a) as they underwent functional magnetic resonance imaging (fMRI) of brain activity. In the LCT, participants are presented with several lottery trials with varying expected values constituted by different probabilities of winning (which is simultaneously losing) different magnitudes of points at stake. Stakes ranged from high probabilities of winning high magnitudes to low probabilities of losing low magnitudes. Participants decided whether to accept or decline the given stakes for each trial, after which outcome feedback was provided. In principle, decisions in the LCT can be made based purely on the information about expected value that is clearly available in each trial. Behaviorally, however, older adults showed higher acceptance rates of stakes with a lower probability of winning (or higher probability of losing) than younger adults (Figure 1b). This result reflects greater risk-taking preferences in older adults than younger adults, who were more risk-neutral.

   Crucially, fMRI measurements identified stark age differences in the brain areas sensitive to changes in expected values in young and older adults (Figure 2). In young adults, a higher probability of winning evoked higher neural activity in the ventral striatum (Figure 2a). This is expected because the ventral striatum is innervated by dopaminergic neurons and has been implicated in reward learning. Thus, younger adults engage this reward processing brain area when weighing between outcome values of behavioral options given the stimuli.

   In contrast, in older adults, a higher probability of winning evoked higher neural activity in the medial temporal and medial prefrontal areas of the brain instead of in the ventral striatum (Figure 2b). Although implicated in value and reward processing, these regions are also part of brain systems involved in affective and emotional processing. In addition, older adults also engaged lateral prefrontal areas, but unlike that in the other areas, the higher neural activity here was engaged for a higher probability of losing rather than winning. This reversal in the trend of neural activity in lateral frontal areas reflects the engagement of regulatory processes, perhaps to downplay the negative emotions older adults might experience when processing likely losses, which culminates in increasing their propensity to accept risks. Furthermore, higher expression of this altered pattern of neural processing of value in older individuals increased behavioral risk-taking in the LCT (Figure 2c). Thus, older adults recruit additional and distinct neural circuitry compared to younger adults to integrate the same objective value information. This age-related involvement of a wider network of brain regions during value-based decisions is associated with higher valuation of stakes with expected losses.

   Future studies are needed to further tease apart specific factors and mechanisms that cause older adults to show neural network engagement so different from that of younger adults when processing value information. For now, these data reveal that there are age differences in the neural processing of objective value that influence the way older adults make financial decisions (e.g., buying health products, insurance policies, financial investments). Essentially, there is a shift from relatively straightforward ventral striatal processing of objective value in young adults to more extensive involvement of frontal and medial temporal processing in older adults, suggesting more deliberative considerations of value in a manner that potentiates risk-taking in the latter.

Figure 1. (a) An example trial of the lottery choice task (LCT) in which participants choose whether to accept or reject the given stakes, followed by the outcome. In this instance, there is a 76% chance of winning 94 points (which is also a 24% change of losing the same points). A ‘win’ outcome is depicted so that the participant gains 94 points (making the cumulative total 304 points; top outcome) if he or she accepts the stake but misses the points otherwise (bottom outcome shown in parenthesis). Each stimulus is separated from the others by interstimulus intervals (ISI). (b) Mean acceptance rates of young and older adult participants in the study (error bars showing standard error of measurement) over different levels of stake probabilities. Older adults were significantly (* p < 0.05) more likely than younger adults to accept stakes with lower probabilities of winning (10%, 30%, 50%; i.e., higher probability of losing).

Figure 2. (a) Young adults primarily engaged higher ventral striatal activity in response to increasing probability of winning (in orange). (b) Ventral striatal responses were not observed in older adults. Instead, older adults engaged higher medial temporal lobe and medial prefrontal cortex neural activity to increasing probability of winning (in orange) and higher lateral prefrontal cortex to decreasing probability of winning (increasing probability of losing) (in blue). (c) In older adult lateral prefrontal areas, more negative neural sensitivity to increasing probability of winning (i.e., higher neural responses to probability of losing) significantly correlated with lower risk aversion (i.e., greater risk-taking).

Su, Y., Chen, J., Tang, Y., Yuan, S., McCarrey, A., & Goh, J. (2018). Age-related differences in striatal, medial temporal, and frontal involvement during value-based decision processing. Neurobiology of Aging, 69, 185-198. doi:10.1016/j.neurobiolaging.2018.05.019

Joshua O. S. Goh
Assistant Professor, Graduate Institute of Brain and Mind Sciences, College of Medicine 

Yu-Shiang Su
Graduate Institute of Brain and Mind Sciences, College of Medicine



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