Anticipatory energization revealed by pupil and brain activity guides human effort-based decision making.

An organism's fitness is determined by how it chooses to adapt to effort in response to challenges. Exertion of effort correlates with activity in dorsomedial prefrontal cortex (dmPFC) and noradrenergic pupil dilation, but little is known about the role of these neurophysiological processes for decisions about future efforts - they may provide anticipatory energization to help us accept the challenge or a cost representation that is weighted against the expected rewards. Here we provide evidence for the former, by measuring pupil and fMRI brain responses while 52 human participants (29 females) chose whether to exert efforts to obtain rewards. Both pupil-dilation rate and dMPFC fMRI activity increased with anticipated effort level, and these increases differ depending on the choice outcome: They were stronger when participants chose to accept the challenge compared to when the challenge was declined. Crucially, the choice-dependent modulation of pupil and brain-activity effort representations were stronger in participants whose behavioral choices were more sensitive to effort. Our results identify a process involving the peripheral and central human nervous system that simulates the required energization prior to overt response, suggesting a role in guiding effort-based decisions.SIGNIFICANCE STATEMENT:The brain's arousal system tracks the effort we engage in during strenuous activity. But much less is known about what role this effort signaling may play when we decide whether to exert effort in the future. Here we characterize pupil-linked arousal and brain signals that guide decisions whether to engage in effort to gain money. During such choices, increases in brain activity and pupil dilation correlated with the effort involved in the chosen option, and these increases were stronger when people decided to accept the effort compared to when they rejected it. These results suggest that the brain arousal system guides decisions by energizing the organism for the prospective challenge.