Fig. 1: Inverted U-shaped relationship between arousal and whole-brain FC in human detection task and resting states.

A Human detection task fMRI with simultaneous pupil size recording. B U-shaped response time and inverted U-shaped correction rate with the increasing arousal level as indexed by the pupil size (8 bins). Behavioral performance was fitted to a quadratic curve y = β₂x² + β₁x + β₀, and the β₂ < 0 represented an inverted U-shaped profile. C Arousal modulated inverted U-shaped whole-brain FC changes in human detection task. The task block structure was regressed out from the BOLD signals before the dynamic FC estimation. D, E Significant correlation between behavioral performance and arousal sorted dynamic FC. Each dot represented an individual arousal bin as in (B, C). Red or blue line, the best linear fitting. Solid line (or shade) in (B, C), the best fitting of quadratic curve (or the 95% prediction interval). Sample size in (B–E): n = 52 runs for each bin. Error bar in (B–E), the standard error of the mean (SEM). F Human EEG-fMRI with simultaneous eye-tracking and button-pressing recording. G Inverted U-shaped relationship between whole-brain global dynamic FC and arousal level in awake state. The EEG power spectrum, global FC, pupil size, and button-press rate were sorted and averaged along with the increasing arousal level as indexed by EEG (30 bins). Black solid line (or shade), the best fitting of quadratic curve (or the 95% prediction interval). Sample size n = 158 runs for each bin. Error bar, the SEM. H Quantitative evaluations of arousal aligned dynamic FC, pupil size, and button-press rate changes. Thirty arousal bins in (G) were further trisected into three bins, i.e., low, middle, and high. Sample size n = 10 bins for each arousal level. Error bar, the SEM. Statistical significance was determined by the paired t-test (two tails). n.s. no significance; *, p < 0.05; **, p < 0.01. I Arousal modulated whole-brain spatial pattern of global FC changes. Upper, global FC difference of middle minus low arousal level; lower, that of high minus middle arousal level. Source data are provided as a Source Data file.