Resting‐State fMRI Study of Vigilance Under Circadian and Homeostatic Modulation Based on Fractional Amplitude of Low‐Frequency Fluctuation and Regional Homogeneity in Humans Under Normal Entrained Conditions

BACKGROUND: How brain neural activity changes at multiple time points throughout the day and the neural mechanisms underlying time-dependent modulation of vigilance are less clear. PURPOSE: To explore the effect of circadian rhythms and homeostasis on brain neural activity and the potential neural basis of time-dependent modulation of vigilance. STUDY TYPE: Prospective. SUBJECTS: A total of 30 healthy participants (22-27 years old). FIELD STRENGTH/SEQUENCE: A 3.0 T, T1-weighted imaging, echo-planar functional MRI (fMRI). ASSESSMENT: Six resting-state fMRI (rs-fMRI) scanning sessions were performed at fixed times (9:00 h, 13:00 h, 17:00 h, 21:00 h, 1:00 h, and 5:00 h) to investigate fractional amplitude of low-frequency fluctuation (fALFF) and regional homogeneity (ReHo) diurnal variation. The fALFF/ReHo and the result of the psychomotor vigilance task were used to assess local neural activity and vigilance. STATISTICAL TESTS: One-way repeated measures analysis of variance (ANOVA) was used to assess changes in vigilance (P < 0.05) and neural activity in the whole brain (P < 0.001 at the voxel level and P < 0.01 at the cluster level, Gaussian random field [GRF] corrected). Correlation analysis was used to examine the relationship between neural activity and vigilance at all-time points of the day. RESULTS: The fALFF/ReHo in the thalamus and some perceptual cortices tended to increase from 9:00 h to 13:00 h and from 21:00 h to 5:00 h, whereas the key nodes of the default mode network (DMN) tended to decrease from 21:00 h to 5:00 h. The vigilance tended to decrease from 21:00 h to 5:00 h. The fALFF/ReHo in the thalamus and some perceptual cortices was negatively correlated with vigilance at all-time points of the day, whereas the fALFF/ReHo in the key nodes of the DMN was positively correlated with vigilance. DATA CONCLUSION: Neural activities in the thalamus and some perceptual cortices show similar trends throughout the day, whereas the key nodes of the DMN show roughly opposite trends. Notably, diurnal variation of the neural activity in these brain regions may be an adaptive or compensatory response to changes in vigilance. EVIDENCE LEVEL: 1. TECHNICAL EFFICACY: 1.