Prefrontal connections express individual differences in intrinsic resistance to trading off honesty values against economic benefits

Abstract

Individuals differ profoundly when they decide whether to tell the truth or to be dishonest, particularly in situations where moral motives clash with economic motives, i.e., when truthfulness comes at a monetary cost. These differences should be expressed in the decision network, particularly in prefrontal cortex. However, the interactions between the core players of the decision network during honesty-related decisions involving trade-offs with economic costs remain poorly understood. To investigate brain connectivity patterns associated with individual differences in responding to economic costs of truthfulness, we used functional magnetic resonance imaging and measured brain activations, while participants made decisions concerning honesty. We found that in participants who valued honesty highly, dorsolateral and dorsomedial parts of prefrontal cortex were more tightly coupled with the inferior frontal cortex when economic costs were high compared to when they were low. Finer-grained analysis revealed that information flow from the inferior frontal cortex to the dorsolateral prefrontal cortex and bidirectional information flow between the inferior frontal cortex and dorsomedial prefrontal cortex was associated with a reduced tendency to trade off honesty for economic benefits. Our findings provide a novel account of the neural circuitry that underlies honest decisions in the face of economic temptations.

Figure 1. Experimental design and behavioral results.

(A) Participants first viewed a fixation cross for a variable ITI of 2–6 s followed by the presentation of a cue (1 s) indicating that participants had to perform the truthtelling task. The first, variable option was then shown for 3 s together with the true earning (31 cents per share). Below the option, the CEO compensation (and the corresponding participant payoff in parentheses) was presented. The payoff of the truthful option varied between CHF 1 and 5. After an interstimulus interval (2–6 s) the second, constant option (5 CHF) was presented together with the first option. The second option was the false report (35 cents per share). Upon presentation of the second option, participants had 2 s to indicate their choice by performing a button press. As soon as they pressed a button, the color of the written text on the screen changed from white to yellow to indicate that a response had been recorded. (B) The difference in the percentage of truthtelling between individuals with stronger and weaker honesty-related values increased as a function of cost. When the economic costs of truthfulness were high, participants with stronger honesty-related values (upper tercile) were more honest compared to those with weaker honesty-related values (lower tercile), suggesting that honesty-related values are more important in determining truthful decisions when the costs of truthfulness are higher. Error bars indicate SEMs.

Figure 2. Activity in DLPFC and DMPFC (seed regions for Fig. 3) reflects truthtelling costs with increasing propensity to be honest.

(A,B) DLPFC responses to the cost of truthtelling increased with the individual percentage of truthtelling (−30, 56, 26; t₍₃₀₎ = 4.92; p < 0.05, whole-brain FWE cluster-level corrected). (C,D) DMPFC responses to the cost of truthtelling increased with the individual percentage of truthtelling (−6, 16, 44; t₍₃₀₎ = 4.48; p < 0.05, whole-brain FWE cluster-level corrected). Throughout, activations are displayed at the uncorrected level of p < 0.001 for visualisation purposes.

Figure 3. DLPFC-IFG and DMPFC-IFG interactions increase with truthtelling costs particularly in individuals with stronger honesty-related values.

Functional connectivity between the honesty-related seed regions DLPFC and DMPFC (shown at smaller scale) and the IFG (DLPFC-IFG: −46, 28, 30; t₍₃₀₎ = 4.56; DMPFC-IFG: −44, 28, 28; t₍₃₀₎ = 5.12; both p < 0.05, whole-brain FWE cluster-level corrected) was increased in high compared to low cost conditions as honesty-related values increased. Voxels in red show correlation with the DLPFC seed, voxels in blue show correlation with the DMPFC seed, and voxels in purple show the overlap between the correlations of the two seed regions. The left graph shows individual connectivity strengths for the DLPFC-IFG interaction and the right graph shows individual connectivity strengths for the DMPFC-IFG interaction. Please note that this figure illustrates the results of a PPI analysis over all subjects. The y-axis shows the coupling difference for high-low cost conditions and the negative values in low honesty value individuals are a consequence of this fact. In other words, for these individuals coupling is higher for low cost than high cost conditions. However, in all conditions, coupling tended to be positive (Supplementary Fig. S4).

Figure 4. DCM models and results of Bayesian model selection.

(A) Illustration of nine alternative model families with changes in connectivity modulated by high cost. Arrows represent potential modulation of coupling between the DLPFC and IFG and the DMPFC and the IFG. Models within a family differed in terms of driving input region (grey dashed arrows: driving inputs could be either into the DLPFC, the DMPFC, the IFG or any combination of these regions). (B) Bar graph showing the exceedance probability for each model family. The labels on the x-axis correspond to the numbers assigned to each model family in A.