Cognitive Control Modulates Effects of Episodic Simulation on Delay Discounting in Aging

Abstract

Enhancing prospective thinking by tagging the future with specific episodic events has been shown to reduce delay discounting in young age ("tag-effect"). So far, it is unclear whether such beneficial effect extends to old adulthood. Since the general ability of future thinking and cognitive control are crucial modulators of temporal discounting in young age, potential age-related decline in these functions might impact on the effect. We focused on this issue by combining functional magnetic resonance imaging (fMRI) with an established intertemporal choice task including episodic "tags" in healthy older participants. Future thinking ability was assessed using autobiographical interviews for future event simulations and a visual search task was applied to assess participants' cognitive control ability. In contrast to previous data in young adults, the group of older participants did not benefit from tagging the future with episodic events. Older participants' cognitive control function was directly associated with discounting rates in the episodic conditions: the less the older adults were able to focus their attention the less they benefited from the inclusion of episodic events. Consistent with this, imaging results revealed that: (a) subjective value (SV) signals in the hippocampus and the anterior cingulate cortex (ACC) as well as; (b) hippocampal-striatal coupling during the episodic condition were positively related to participants' control capacity. Our findings highlight the critical role of executive functioning for the simultaneous integration of episodic information with future value computation in aging. Boosting delay gratification by including episodic tags might hence be limited in older individuals with pronounced decline in distraction control.

Keywords: aging; cognitive control; delay discounting; episodic prospection; impulsivity.

Figure 1

Outline of the paradigm. Each trial started with a green dot, signaling the start of the trial. Then, the delayed reward option was presented for 6 s and participants had to either imagine the event in the café (episodic conditions) or not imagine anything in the control condition. Subsequently, participants had to indicate their choice by selecting the red cross for the immediate reward (20€ that were not shown) or the green check mark for the delayed reward option.

Figure 2

Attentional control paradigm. The task is to respond to the symbol depicted in the target shape (circle) and ignore the singleton distractor (A). Demands on flexible attentional control can be raised by including trials in which the singleton can become the target (B) so that it cannot be blanked out from the start.

Figure 3

Behavioral data. (A) In comparison to younger adults (Sasse et al., 2015), discounting behavior did not significantly differ between the two episodic conditions and the control condition in older adults. (B) Differences between the two conditions in older age were related to individual differences in attentional control ability (singleton score). **p < 0.05.

Figure 4

Activation differences between episodic and control conditions. Greater activation for the episodic conditions compared to the control condition was observed in the left ventromedial prefrontal cortex (vmPFC) and the left precuneus (all p < 0.05 FWE). Activations are overlaid on the mean structural image of all participants (display threshold p < 0.005 uncorrected).

Figure 5

Correlations between attentional control ability and neural modulation by subjective value (SV; parametric analysis) for the episodic compared to the control condition. Significant correlations were found in the right anterior cingulate cortex (ACC) and the left hippocampus (all p < 0.05 FWE). Plots show the separate correlations in the peak voxels of the ACC and hippocampus. Activations are overlaid on the mean structural image of all participants (display threshold p < 0.005 uncorrected).

Figure 6

Correlation between attentional control ability and hippocampal coupling. Individual control ability (singleton score) was related to functional coupling between the left hippocampus and the left ventral striatum in the episodic compared to the control condition (p < 0.05 FWE). The plot demonstrates the correlation in the peak voxel of the left ventral striatum. Activations are overlaid on the mean structural image of all participants (display threshold p < 0.005 uncorrected).