Mental effort and brain stimulation did not simply push decision-making in opposite directions. Instead, their combination changed some kinds of exploration while leaving other choices unaffected. Experience-based decision making requires a balance between exploration and exploitation under uncertainty, and that balance may be influenced by cognitive demands and prefrontal neuromodulation.

The study examined trivia-based cognitive load and anodal transcranial direct current stimulation over the left dorsolateral prefrontal cortex in 60 healthy adults. Participants completed 50 decisions involving a safe choice, a probabilistic high-reward choice, and a costly information-seeking choice.

Human decision making in uncertain environments requires a continuous balance between exploring new alternatives and exploiting familiar options that have yielded favorable outcomes in the past. Human decision making in uncertain environments involves an exploration-exploitation trade-off: balancing new alternatives against familiar options that have yielded favorable outcomes in the past.

Cognitive load can limit working-memory and attentional resources, while the dorsolateral prefrontal cortex supports goal maintenance, feedback integration, and flexible adjustment of behavior. Transcranial direct current stimulation provides an experimental method for examining whether modulation over the DLPFC is associated with changes in decision behavior.

The direction and magnitude of stimulation effects depend on stimulation parameters, task demands, and individual differences. Previous studies have generally examined cognitive load and prefrontal stimulation separately. It therefore remained unclear whether concurrent cognitive demand and anodal DLPFC stimulation would produce broadly additive effects or whether stimulation would change under additional cognitive demand.

The study addressed this question with a repeated decision-from-experience task containing safe, risky, and information-seeking alternatives. The primary experiment used a two-by-two between-subjects design crossing anodal tDCS versus sham with Trivia-Based Load versus No-Trivia Control.

Within the Trivia-Based Load condition, Lower-Load and Higher-Load Trivia were presented across trials for a secondary trial-level analysis. The study examined reaction time, risky choice, information seeking, and alternation rate as related but distinct indicators of decision behavior under uncertainty.

Selecting the probabilistic high-reward alternative was treated as an index of risk-taking because it accepted the possibility of no reward for a substantially larger potential gain than the guaranteed safe option. Selecting the costly reveal alternative was treated as information seeking because participants paid one point to obtain otherwise unavailable probability information before making their final choice.

Alternation rate represented exploratory switching because it measured changes between choice types across successive trials, although higher alternation could also reflect weaker commitment or unstable value learning. These measures were interpreted as complementary rather than interchangeable indicators of exploration-exploitation behavior.

Two theoretical patterns were possible because cognitive load and anodal DLPFC stimulation were expected to exert opposing directional influences on some outcomes. Under a partially independent account, cognitive load would constrain working-memory and attentional resources, while anodal stimulation would modulate prefrontal contributions to exploratory control, producing broadly additive effects.

Alternatively, if stimulation strengthened the same processes disrupted by cognitive load, its behavioral effect could differ across Cognitive-Load Conditions, producing a compensatory or context-dependent interaction. The primary experiment followed a two-by-two between-subjects factorial design with Stimulation and Cognitive-Load Condition as between-subject factors.

The four groups were anodal tDCS with Trivia-Based Load, anodal tDCS with No-Trivia Control, sham with Trivia-Based Load, and sham with No-Trivia Control. Participants in the Trivia-Based Load condition answered a trivia question before each decision trial, whereas participants in the No-Trivia Control condition proceeded directly to the decision task.

Within the Trivia-Based Load condition, Trial-Level Cognitive Load was manipulated by presenting 25 Lower-Load and 25 Higher-Load Trivia questions in randomized order. Transcranial direct current stimulation was delivered using the Neuroelectrics Starstim 32 system, a wireless multichannel stimulator with real-time monitoring of electrode contact quality.

The electrodes were positioned using a neoprene headcap according to the international ten-ten EEG system. The anodal electrode was placed at F3 to target the left DLPFC, with return electrodes over the right supraorbital region at Fp2 and AF4. In the stimulation views, the voltage map shows a clear left-to-right gradient across the cortical surface, while the electric-field map concentrates stronger colors over the central and left cortical regions.

The orthogonal slices in panels B and C show that these modeled effects extend through multiple viewing planes rather than appearing only on the outer surface. The decision-making task consisted of 50 trials, and each trial required participants to select among three alternatives.

In the Trivia-Based Load condition, each trial began with a trivia question and feedback on the trivia response, followed by the decision phase. Figure three lays out one complete decision trial. In the Trivia-Based Load condition, participants first answer a general-knowledge question, receive feedback, choose between safe, risky, or costly information-seeking options, and then see the outcome; the example shows a risky choice earning seventeen point five two points.

This sequence matters because it makes clear where the cognitive load occurs and how information seeking is embedded before the final safe-or-risky decision. The safe choice provided a guaranteed outcome between 2.5 and 3.5 points, with values jittered uniformly across trials.

This safe choice, labeled Option A, guaranteed an outcome between two point five and three point five points, with its value varied uniformly across trials. Risk-taking was defined as the proportion of trials on which the risky choice was selected, while information seeking was defined as the proportion of trials on which the costly information-seeking choice was selected.

Alternation rate was the proportion of successive trial transitions involving a switch between the safe choice and the risky choice. Mean decision reaction time was calculated from presentation of the decision screen to the participant’s response. The measures were analyzed separately because they represent related but distinct components of decision behavior.

The primary factorial analyses produced different patterns across reaction time, risky choice, information seeking, and alternation rate. Cognitive-Load Condition significantly affected reaction time and risky choice, while Stimulation significantly affected risky choice, information seeking, and alternation rate.

The Stimulation by Cognitive-Load Condition interaction was significant for information seeking and alternation rate, but not for reaction time or risky choice. The findings therefore did not support a uniform additive pattern across all outcomes.

Figure four shows that decision reaction time was three point two seven seconds in the No-Trivia Control and four point three five seconds under Trivia-Based Load, with a significant difference marked at p equals .045. The error bars show ninety-five percent confidence intervals, supporting the authors’ conclusion that added cognitive load was associated with slower responses.

Figure five shows two main effects on the proportion of risky choices. In panel A, the mean is zero point three three nine under Sham and zero point five nine three under tDCS, with a reported p-value below zero point zero zero one. Panel B reports zero point five zero one for the No-Trivia Control and zero point four three one for the Trivia-Based Load, again with a p-value below zero point zero zero one; the error bars show ninety-five percent confidence intervals.

Information seeking was higher overall under anodal tDCS than under sham stimulation. The main effect of Cognitive-Load Condition was not significant. However, the Stimulation by Cognitive-Load Condition interaction was significant, with a crossover pattern in the cell means.

Figure six shows that information-seeking choices differed between sham and tDCS stimulation overall, with means of zero point two five eight and zero point three one eight, respectively, and a reported p-value of zero point zero zero eight. Panel B shows that this stimulation pattern depended on cognitive-load condition: under the no-trivia control, the means were zero point two nine five for sham and zero point two seven five for tDCS, whereas under trivia-based load they were zero point two two one and zero point three six one.

The interaction was reported as significant, with a p-value of zero point zero zero one. Alternation rate was higher overall under anodal tDCS than under sham stimulation. The main effect of Cognitive-Load Condition was not significant, but the Stimulation by Cognitive-Load Condition interaction was significant.

Under sham, alternation was numerically lower with Trivia-Based Load than with No-Trivia Control, whereas under anodal tDCS alternation was numerically higher with Trivia-Based Load than with No-Trivia Control. This crossover pattern indicates context-dependent modulation rather than a uniform additive effect, but the interaction should be interpreted cautiously because Levene’s test was significant for alternation rate.

In panel B, the No-Trivia Control bars are closely spaced, labeled point one four five for sham and point one five eight for tDCS. In the Trivia-Based Load pair, the bars are farther apart, with labels point one two zero and point two one six; the error bars show the uncertainty around each mean.

The study combined anodal tDCS over the left DLPFC with a trivia-based cognitive-load manipulation in a repeated three-option decision-from-experience task. Concurrent trivia slowed responses and reduced risky choice, while anodal tDCS was associated with greater risky choice, information seeking, and exploratory switching.

Reaction time and risky choice showed no significant Stimulation by Cognitive-Load Condition interaction, whereas information seeking and alternation showed significant crossover interactions. The findings are most consistent with outcome-specific modulation, including both additive and context-dependent effects.

The results provide behavioral evidence that cognitive demand and prefrontal stimulation jointly shape decision making under uncertainty, while the underlying neurophysiological mechanisms remain to be established by future work. Cognitive load and left-DLPFC stimulation shape different parts of uncertain decision-making, with stimulation increasing risk-taking and exploration but interacting with load specifically for information seeking and switching.

The effects are outcome-specific, not one-size-fits-all.