Effect of Brain Stimulation on Effort Is Task Dependent: Evidence From an HD-tDCS Study on Cardiovascular Responses

Area of Science:

• Neuroscience
• Cognitive Psychology
• Psychophysiology

Background:

• Frontal hemispheric asymmetry (FHA) is linked to approach and withdrawal motivations.
• The dorsolateral prefrontal cortex (dlPFC) plays a crucial role in cognitive control and effort-based decision-making.
• Neuromodulation techniques offer a way to investigate the causal role of specific brain regions in cognitive processes.

Purpose of the Study:

• To investigate the causal effect of manipulating FHA on mental effort.
• To examine how modulating the dlPFC influences cardiovascular responses associated with effort.
• To determine if task difficulty (fixed vs. unfixed) moderates the effect of FHA on mental effort.

Main Methods:

• Utilized high-definition transcranial direct current stimulation (HD-tDCS) to induce FHA by applying cathodal stimulation to either the left or right dlPFC.
• Participants (N=43) performed two tasks: a fixed, easy task and an unfixed, self-paced task with monetary incentives.
• Measured cardiovascular responses, including pre-ejection period (PEP), as an index of mental effort.

Main Results:

• Right cathodal stimulation, expected to induce left FHA, significantly increased PEP reactivity (higher effort) in the unfixed task condition compared to left cathodal stimulation.
• No significant effect of stimulation was observed in the fixed, easy task condition.
• Cardiovascular responses (SBP, HR, DBP) were also monitored, with PEP reactivity serving as the primary indicator of effort.

Conclusions:

• Neuromodulation of the dlPFC via HD-tDCS can alter mental effort intensity by shifting FHA.
• Increased FHA enhances the perceived importance of success, leading to greater effort allocation in tasks with variable demands.
• These findings provide causal evidence for the role of FHA in regulating effort-based motivation and performance.