Coupling between pupil fluctuations and resting-state fMRI uncovers a slow build-up of antagonistic responses in the human cortex

- A link is revealed between resting-state pupil diameter and fMRI-BOLD fluctuations.
- This link exhibits robust cortical spatiotemporal correlation patterns.
- Pupil correlations uncover extrinsic (sensorimotor) vs. intrinsic (DMN) antagonism.
- Accumulator-like dynamics in specific DMN hubs are shown to predict pupil dilation.

Even in absence of overt tasks, the human cortex manifests rich patterns of spontaneous “resting state” BOLD-fMRI fluctuations. However, the link of these spontaneous fluctuations to behavior is presently unclear. Attempts to directly investigate this link invariably lead to disruptions of the resting state. Here we took advantage of the well-established association between pupil diameter and attentional gain to address this issue by examining the correlation between the resting state BOLD and pupil fluctuations. Our results uncover a spontaneously emerging spatiotemporal pupil-BOLD correlation whereby a slow buildup of activity in default mode areas preceded both pupil dilation and wide-spread BOLD suppression in sensorimotor cortex. Control experiments excluded a role for luminance fluctuations or fixation. Comparing the pupil-correlated patterns to activation maps during visual imagery revealed a substantial overlap. Our results indicate a link between behavior, as indexed by pupil diameter, and resting state BOLD fluctuations. These pupil dilations, assumed to be related to attentional gain, were associated with spontaneously emerging antagonism between fundamental cortical networks.