Taking a gamble or playing by the rules: dissociable prefrontal systems implicated in probabilistic versus deterministic rule-based decisions

Abstract

A decision may be difficult because complex information processing is required to evaluate choices according to deterministic decision rules and/or because it is not certain which choice will lead to the best outcome in a probabilistic context. Factors that tax decision making such as decision rule complexity and low decision certainty should be disambiguated for a more complete understanding of the decision making process. Previous studies have examined the brain regions that are modulated by decision rule complexity or by decision certainty but have not examined these factors together in the context of a single task or study. In the present functional magnetic resonance imaging study, both decision rule complexity and decision certainty were varied in comparable decision tasks. Further, the level of certainty about which choice to make (choice certainty) was varied separately from certainty about the final outcome resulting from a choice (outcome certainty). Lateral prefrontal cortex, dorsal anterior cingulate cortex, and bilateral anterior insula were modulated by decision rule complexity. Anterior insula was engaged more strongly by low than high choice certainty decisions, whereas ventromedial prefrontal cortex showed the opposite pattern. These regions showed no effect of the independent manipulation of outcome certainty. The results disambiguate the influence of decision rule complexity, choice certainty, and outcome certainty on activity in diverse brain regions that have been implicated in decision making. Lateral prefrontal cortex plays a key role in implementing deterministic decision rules, ventromedial prefrontal cortex in probabilistic rules, and anterior insula in both.

Fig. 1

Stimuli and timing in choice task. Participants saw a cue (Choice screen), made a response, saw an initial feedback stimulus (Fbk1 screen; immediate partial feedback: ‘+’/‘−’, or delayed feedback: ‘?’; delayed feedback occurred in probabilistic choice trials only), waited through a delay (Delay screen), then received final feedback (Outcome screen; ‘+’ or ‘−’ 20¢ or 1¢) showing valence and magnitude of the trial outcome.

Fig. 2

Behavioral results for choice task. Left bar graph shows mean response times, right bar graph shows mean frequency that participants selected the optimal response on high choice certainty probabilistic, low choice certainty probabilistic, and complex rule-based choices. ‘*’ indicates significant difference (two-tailed, p<.05). Error bars represent standard error of the mean.

Fig. 3

VLPFC and DACC regions of interest defined by the complex rule-based choice versus high choice certainty probabilistic choice contrast. Center column shows t-statistic maps from the complex rule-based choice versus high choice certainty probabilistic choice contrast (top: VLPFC, bottom: DACC; threshold at p<.001 uncorrected, 10 contiguous voxels), (a) Choice phase parameter estimates for high choice certainty probabilistic, low choice certainty probabilistic, and complex rule-based conditions, (b) Outcome phase parameter estimates for probabilistic choice positive outcomes, probabilistic choice negative outcomes, and complex rule-based positive outcomes. Significant differences (two-tailed, p<.05) are denoted in (b) with a ‘*’. (c) VLPFC (top) and DACC (bottom) activation time course for high choice certainty probabilistic, low choice certainty probabilistic, and complex rule-based conditions. Onset of the choice phase corresponds to 0 s. Error bars in each chart represent the standard error of the mean.

Fig. 4

VMPFC region of interest defined by the high choice certainty probabilistic versus low choice certainty probabilistic contrast, and right anterior insula (R Insula) region defined by the conjunction of the low choice certainty probabilistic versus high choice certainty probabilistic contrast with the complex rule-based choice versus high choice certainty probabilistic choice contrast, (a) Choice phase parameter estimates for high choice certainty probabilistic, low choice certainty probabilistic, and complex rule-based conditions (VMPFC: top, R Insula: bottom), (b) VMPFC in t-statistic map from the high choice certainty probabilistic choice versus low choice certainty probabilistic choice contrast, (c) R Insula significant voxels from conjunction of the low choice certainty probabilistic versus high choice certainty probabilistic contrast with the complex rule-based choice versus high choice certainty probabilistic choice contrast, (d) VMPFC (top) and R Insula (bottom) activation time course for high choice certainty probabilistic, low choice certainty probabilistic, and complex rule-based conditions. Onset of the choice phase corresponds to 0 s. (e) Outcome phase parameter estimates for probabilistic choice positive outcomes, probabilistic choice negative outcomes, and complex rule-based positive outcomes (VMPFC: top, R Insula: bottom). Significant differences are noted in the bar graphs in (e) with a ‘*’. Error bars in each chart represent the standard error of the mean.