# Functional imaging of time on task and the involvement of dopaminergic and cholinergic substrates in cognitive effort and reward

## TL;DR

This study explores how the brain manages increasing cognitive effort over time and how rewards influence this process, highlighting the role of specific brain regions.

## Contribution

The study identifies the basal forebrain as a key region involved in sustaining cognitive effort modulated by reward levels.

## Key findings

- Activity related to time on task peaks in the anterior cingulate cortex and involves motor and somatosensory regions.
- The ventral striatum reflects reward levels but not effort-reward trade-offs.
- The basal forebrain shows increased activity with time on task and is sensitive to reward levels.

## Abstract

Neuroimaging studies have identified the neural substrates associated with sustained cognitive efforts and control and their modulation by rewards. Different lines of evidence implicate the prefrontal cortex (especially the anterior cingulate cortex, ACC), dopaminergic, and cholinergic substrates in this modulation. We studied here the activity of these substrates at increasing time on task (requiring increasing levels of cognitive effort) in trials within blocks with differing reward levels. In the cortex, while peaking in the ACC, activity associated with time on task was extensive, also including activity decrements outside the default mode network, primarily involving motor and somatosensory regions. Information about reward levels was carried in the ventral striatum, consistent with its motivational role, but did not reflect trade-offs with increasing efforts during time on task. Instead, the ventral tegmental area and parts of the basal forebrain (BF) corresponding to the cholinergic Ch4 nuclei increased in activity with time on task and were sensitive to reward levels. This BF activity is consistent with a cholinergic role in driving compensatory efforts modulated by reward levels. These findings identify the BF as a neuroimaging phenotype associated with sustaining task sets and cognitive efforts.

The online version contains supplementary material available at 10.1038/s41598-026-37370-9.