# High‐Definition tDCS of the DLPFC: Effects on Effort‐Related Cardiac Reactivity Across Sexes

## TL;DR

This study shows that stimulating the brain's dlPFC can increase effort-related heart responses in both men and women during tasks where rewards depend on performance.

## Contribution

The study extends previous neuromodulation findings to both sexes and demonstrates sex-generalizable effects of dlPFC stimulation on reward-driven effort.

## Key findings

- Right cathodal stimulation increased pre-ejection period reactivity in unfixed tasks compared to left cathodal stimulation.
- Cardiovascular effort remained low in fixed tasks regardless of stimulation condition.
- Effects were observed in both male and female participants, confirming generalizability across sexes.

## Abstract

This study was designed to examine the effect of frontal hemispheric asymmetry (FHA) on effort‐related cardiovascular responses. High‐definition transcranial direct current stimulation (HD‐tDCS) was applied to the dorsolateral prefrontal cortex (dlPFC) to manipulate FHA and investigate its impact on cardiovascular reactivity. The sample consisted of 45 female and 44 male participants, who received either left or right cathodal stimulation. Following stimulation, participants performed two types of task demands: one fixed and easy, the other unfixed. In both tasks, participants could earn a moderate monetary reward. We measured pre‐ejection period (PEP), heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP). Drawing on motivation intensity theory (MIT), we predicted that right cathodal stimulation (left FHA) would lead to higher perceived success importance to get the reward determining higher effort in the unfixed task demand compared to the left cathodal stimulation and both stimulation conditions in the fixed task. As predicted, PEP reactivity was stronger in the unfixed condition following right cathodal stimulation compared to left cathodal stimulation and both stimulation conditions in the fixed task. Importantly, this effect was observed across both female and male participants, extending earlier neuromodulation findings (previously shown only in female samples) to both sexes. Overall, the results indicate that dlPFC neuromodulation can lead to higher effort by shifting frontal asymmetry and enhancing the perceived success importance in reward‐driven tasks.

This study advances our understanding of approach motivation and effort by demonstrating that frontal hemispheric asymmetry modulates HD‐tDCS effects on effort‐related cardiac responses across both male and female participants. Right cathodal stimulation over the dlPFC (inducing greater relative left frontal hemispheric asymmetry) increased pre‐ejection period reactivity compared to left cathodal stimulation, but only within an unfixed task demand context where participants could earn monetary rewards through self‐paced performance. In contrast, when task demand was fixed and easy (requiring only 50% accuracy to earn rewards), cardiovascular effort remained consistently low regardless of the stimulation condition. Critically, these neuromodulation effects were observed across both sexes, extending previous findings that were limited to female samples and establishing the generalizability of dlPFC stimulation effects on reward‐motivated effort.