Effect of homeostatic pressure on daytime vigilance performance: Evidence from behaviour and resting-state EEG.

Vigilance is highly sensitive to the time-of-day effect and goes through the daytime trough during the period of the post-noon dip. A midday nap could maintain individuals' vigilance at an optimal level. Thus, homeostatic sleep pressure is one of the main reasons for the post-noon dip in daytime vigilance. The current study focussed on the role of homeostatic sleep pressure in the diurnal variation of vigilance performance with normal circadian rhythms and the corresponding neural basis. With 34 healthy adults, we recorded the resting-state electroencephalogram activities and the following vigilance performance measured by psychomotor vigilance test in the morning, the no-nap mid afternoon, and the nap mid afternoon. The circadian process was controlled by measuring vigilance and resting-state electroencephalogram activities at the same time point in the nap and no-nap conditions. Homeostatic sleep pressure accumulated from morning to mid afternoon induced the declined vigilance performance and a global increase in resting-state delta, theta, alpha, and beta1 bands power, and a local increase in beta2 band power in the central region. Furthermore, the more the spontaneous beta2 power increased, the less vigilance declined from morning to mid afternoon. The current findings suggest that homeostatic sleep pressure increased cortical excitability but decreased cortical communication efficiency from morning to mid afternoon. In addition, the activity of the high beta waves probably reflected the compensatory effort to counteract the negative impact of the low arousal state on the following vigilance task by performing more action preparation in the no-nap afternoon.

Identification and molecular mechanism of a tri-peptide inhibitor targeting iNOS from duck embryo protein hydrolysates by experimental and bioinformatics studies.

Duck embryonic proteins are a promising source of food-derived functional peptides. Using a combination of experiments and bioinformatics approaches, a tri-peptide inhibitor YPW targeting iNOS was identified from duck embryo protein hydrolysates. Our results indicated that YPW could significantly inhibit LPS-induced NO generation in macrophages in a dose-dependent manner. YPW also significantly inhibited the expression of IL-6 and iNOS. Molecular simulations revealed that YPW could interact strongly with (iNOS) with a binding energy of -45.71 ± 17.75 kJ/mol. The stability of YPW-iNOS was maintained by the hydrogen bonds of amino acid residues Ile195, Gly196, Gly365, Glu371, Asn364, and Trp366, and the hydrophobic interactions by Trp188, Phe363, and Val346. In conclusion, our study provides a new idea for broadening the utilization of duck embryo proteins, and a strategy for the discovery of food-derived bioactive peptides.

How the time-of-day affects the EEG signatures of vigilance fluctuation.

Previous research suggested the homeostatic effect on the top-down control system as a major factor for daytime vigilance decrement, yet how it alters the cognitive processes of vigilance remains unclear. Using EEG, the current study measured the vigilance of 28 participants under three states: the morning, the midafternoon after napping and no-nap. The drift-diffusion model was applied to decompose vigilant reaction time into decision and non-decision components. From morning to midafternoon, vigilance declined during sustained wakefulness, but remained stable after midday napping. Increased sleep pressure negatively affected decision time and drift rate, but did not significantly alter the non-decision process. Frontocentral N2 amplitude decreased from morning to no-nap afternoon, associated with slowing decision time. In contrast, parietal P3 had no diurnal alterations during sustained wakefulness, but enhanced after napping. Pre-stimulus parietooccipital alpha power enhanced under high sleep pressure relative to low, accompanied by more lapses in no-nap vs. post-napping conditions. The homeostasis effect is a major contributor to daily vigilance fluctuation, specifically targeting top-down control processes during the pre-stimulus and decision-making stages. Under the influence of sleep homeostasis, the speed of decision-making declines with degradation in target monitoring from morning to afternoon, leading to post-noon vigilance decrement.