Neural Mechanisms Underlying Motivation of Mental Versus Physical Effort

Schmidt, Liane; Lebreton, Maël; Cléry-Melin, Marie-Laure; Daunizeau, Jean; Pessiglione, Mathias · 2012 · OpenAlex-citations

DOI: 10.1371/journal.pbio.1001266

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Summary

This study investigates the neural mechanisms underlying incentive motivation for mental versus physical effort, specifically addressing whether these distinct types of effort are driven by a common motivational center or by separate, dedicated modules. While previous research established that cognitive and motor systems involve different cortical and basal ganglia networks sensitive to reward, the functional link between the brain’s valuation system and these task-specific systems remained unclear. The authors hypothesized that a common motivational node would encode expected rewards, correlate with performance, and switch effective connectivity to drive either cognitive or motor regions depending on task demands. To test this, the researchers used functional MRI (fMRI) on healthy participants performing a task that independently varied monetary incentives, cognitive demand, and motor demand. Cognitive effort was manipulated using a numerical Stroop task requiring attention to detect the numerically larger figure, while motor effort involved squeezing a handgrip with varying force levels. Participants aimed to climb a virtual ladder to earn monetary rewards, with incentive levels set at 0.01, 0.1, or 1 Euro. Behavioral analysis confirmed that performance increased with higher incentives and decreased with higher cognitive or motor demands, validating the experimental manipulation. Neuroimaging results identified the ventral striatum (VS) as a common motivational node. VS activity encoded expected rewards regardless of whether the subsequent effort was cognitive or motor. Furthermore, VS activity during effort exertion correlated with behavioral performance levels, independent of task difficulty. Crucially, psychophysiological interaction (PPI) analyses revealed that the VS switched its functional connectivity based on task demand: it connected with the caudate nucleus during high cognitive demand and with the putamen during high motor demand. Dynamic causal modeling (DCM) supported a model where the VS mediates incentive effects by boosting activity in the caudate or putamen depending on the specific task requirement, rather than the task-specific regions modulating the VS. The findings suggest that a single motivational module within the basal ganglia, centered on the ventral striatum, drives both mental and physical efforts. This common node translates expected rewards into effort exertion by selectively engaging task-specific dorsal striatal circuits (caudate for cognitive, putamen for motor). This implies that the interaction between valuation and action systems occurs within the basal ganglia, providing a unified neural mechanism for how incentives motivate diverse forms of behavior.

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• mental demand