How the brain supports effort evaluation, preparation and exertion

Generally, when a making decision whether to do something difficult, the effort involved is considered a cost. With this neuroimaging study we investigated how the brain helps us get motivated to do hard things when it is worth it, focusing on three stages: evaluation of, preparation for, and finally exertion of effort.

Role: Lead Researcher

Methods: fMRI, MRI-compatible eye-tracking, questionnaire administration, A/B Testing

Tools: PsychoPy (Python), R, Python, MATLAB, Eyelink 1000 Plus

Data Collection

I coded an fMRI experiment in Python that received MRI scanner and eye-tracking triggers, and collected data at the hospital scanning facility (N = 41). The participants saw an evaluation-cue (e-cue) which indicated the reward and demand level of the upcoming task, which was followed by preparation-cue (p-cue) telling them to prepare for the task that was about to start. The neural responses to the different reward and demand conditions during the evaluation and preparation phases were the main variables of interest. Additionally, pupil size data and performance data were collected.

Data Analysis & Synthesis

Behavioral data was processed in R, eye-tracking data in Python, and fMRI data in MATLAB. Behavioral and pupil data were fitted with mixed-effects regression models in R, and neural region-of-interest data with ANOVA tests in R. The regions of interest were the anterior cingulate cortex (ACC), ventral tegmental area/substantia nigra (VTA/SN), ventral striatum (VS), and the ventromedial prefrontal cortex (vmPFC). In an exploratory analysis, task-phase pupil size was tested as a variable predicting task performance.

Results & Insights

Traditionally reward-attuned brain regions encode the value of effort and show some preference for easy tasks during evaluation. However, these regions can also assign a motivating signal to effort during preparation, flipping the effort signal from negative to positive. When preparing for effort, expectation of higher cognitive load leads to more activity in the brain regions that support exerting control, particularly when it is worth it.

 

Pupil size was larger during effort exertion (the five sequential Stroop targets) for high reward compared to low reward, but only in the easy condition, with pupil being likely maximally dilated during the harder task (this is one of the most reliable indicators of real-time effort exertion). A larger pupil (+1 SD within-participant) was also associated with faster reaction times.

 

  • While the brain integrates demand and value information at each stage of effort processing, effort is encoded as a cost during evaluation but as a motivating factor during preparation

Pupil size was measured at each phase. In the evaluation phase, the pupil is larger when viewing a high reward e-cue, but only when coupled with high demand. In the preparation phase, the pupil parallels ACC effects and is largest right before completing a high-reward hard task.

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