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Review
, 1235, 1-17

Neuromodulation of Reward-Based Learning and Decision Making in Human Aging

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Review

Neuromodulation of Reward-Based Learning and Decision Making in Human Aging

Ben Eppinger et al. Ann N Y Acad Sci.

Abstract

In this paper, we review the current literature to highlight relations between age-associated declines in dopaminergic and serotonergic neuromodulation and adult age differences in adaptive goal-directed behavior. Specifically, we focus on evidence suggesting that deficits in neuromodulation contribute to older adults' behavioral disadvantages in learning and decision making. These deficits are particularly pronounced when reward information is uncertain or the task context requires flexible adaptations to changing stimulus-reward contingencies. Moreover, emerging evidence points to age-related differences in the sensitivity to rewarding and aversive outcomes during learning and decision making if the acquisition of behavior critically depends on outcome processing. These age-related asymmetries in outcome valuation may be explained by age differences in the interplay of dopaminergic and serotonergic neuromodulation. This hypothesis is based on recent neurocomputational and psychopharmacological approaches, which suggest that dopamine and serotonin serve opponent roles in regulating the balance between approach behavior and inhibitory control. Studying adaptive regulation of behavior across the adult life span may shed new light on how the aging brain changes functionally in response to its diminishing resources.

Conflict of interest statement

Conflicts of interest

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Age-related decline in pre- and post-synaptic dopamine binding mechanisms. (A) Striatal DAT binding (adapted from Ref. with permission from Elsevier Science). (B) Striatal D2 receptor binding (adapted from Ref. with permission from Elsevier Science). (C) D1 receptor binding in frontal cortex (adapted from Ref. with permission from Springer-Verlag). (D) D2 receptor binding in frontal cortex.
Figure 2
Figure 2
(A) Simulating aging-related DA modulation by reduction of stochastic gain tuning. Values of G parameters for younger networks were sampled from the range [0.6–1.0], with a mean of 0.9, whereas values for older networks were sampled from the range [0.1–0.5], with a mean of 0.3. (B) Reduced gain tuning increased random activation variability, indicated by activation distributions of one young network’s and old network’s responses to a noise stimulus across 1,000 trials. (C) Reduced gain tuning also increased within-network cross-trial performance variability in simulated old networks in four simulated episodic memory tasks (adapted with permission from Ref. with permission from Elsevier Science). Stochastic gain tuning captures the inverted-U function relating DA modulation and functional outcomes of (D) memory performance and (E) distinctiveness of activation patterns. To simulate the whole range of dopamine dysfunction from deficient to excessive signaling, mean G values from 0.2 to 4.1 were simulated. Activation patterns presented in (E) correspond to mean G of 0.3 (very low mean G), 1.7 (optimal mean G), and 4.0 (very high mean G).
Figure 3
Figure 3
Activation patterns of two choice options in the simulated prefrontal context module across learning in simulated young (mean G = 1.0) and old (mean gain = 0.3) networks. Across learning, activation levels for choice option with higher reward probability become more distinct from the choice option with no reward. This distinction is, however, less pronounced in the simulated old network.
Figure 4
Figure 4
Schematic overview of the triangle relating aging, neuromodulation, and reward-based learning and decision making.

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