Biology subjects

Zhdanova, I. V.

Publications and source records attributed to Zhdanova, I. V..

3 recordsLinked to original sources

bioRxiv2025

Dual-Resonance Shapes REM Sleep: A Mechanistic Link Between Homeostasis, Circadian Phase, and Sleep Deficit.

How circadian and homeostatic processes interact to shape REM sleep architecture remains unresolved. Here, we empirically confirm the existence of a conserved resonance curve governing REM episode duration, as previously predicted by the wave model of sleep dynamics. This curve emerges from two converging resonance states - homeostatic and circadian - that form a stable framework across conditions. Their relative phase and amplitude determine REM structure, producing bell-shaped, linear, or bimodal profiles. The model reproduces REM dynamics during regular sleep, extension, and post-deprivation recovery. Crucially, REM duration alone provides an experimentally accessible readout: simultaneously revealing circadian phase and quantifying sleep deficit as additional hours needed to restore homeostatic equilibrium. Together, these findings reposition REM duration from a descriptive to a diagnostic marker, and a mechanistic signal, linking sleep architecture to the dynamic interplay of internal regulatory systems. Summary sentenceREM episode duration emerges as a dual readout of circadian phase and sleep deficit, reflecting the interaction of homeostatic and circadian resonance processes.

neuroscience↗

bioRxiv2025

Homeostatic Forces Shaping the Daily Pattern of Sleep Propensity.

The discrepancy between high sleep need and the ability to initiate sleep underlies insomnia, the most prevalent sleep disorder, whose nature remains obscure. Sleep need increases monotonically with prolonged wakefulness, as reflected in the rising intensity of sleep after varying wake intervals. In contrast, sleep propensity - the ability to transition from wake to sleep - follows a bimodal pattern, peaking in the mid-afternoon, dipping in the evening, and rising again near bedtime. Previously, we demonstrated that sleep structure dynamics can be effectively modeled using probability waves. Here, we extend this wave model of homeostatic regulation of sleep to the period of wakefulness and show that its extrapolation predicts the bimodal pattern of wake-to-sleep transitions. This pattern arises from the interplay of two key factors in state transitions: wake-state instability and interaction strength between states. While wake-state instability increases monotonically, interaction strength follows a bimodal pattern. Their combined effect produces a bimodal probability of state transitions, aligning closely with experimental data. The mid-afternoon peak corresponds to maximal interaction at the homeostatic equilibrium of sleep and wake states, whereas the evening dip reflects minimal interaction, counteracting high wake-state instability. An exponential rise in both factors by the end of the day facilitates sleep onset at bedtime. Our experimental findings on sleep deprivation support the model predictions. Understanding the relationship between sleep need and ability to initiate sleep may offer valuable insights for optimizing daytime performance and sleep quality in both health and disease. Statement of significanceMonotonic increase in sleep need throughout the day contrasts sharply with the bimodal pattern of the ability to fall asleep, referred to as sleep propensity. This phenomenon, inherent to normal sleep physiology, may also underlie major insomnias - inability to fall asleep despite high sleep need. We applied the wave model of sleep dynamics to unveil how the bimodal daily sleep propensity pattern can emerge from the non-linear changes in homeostatic strength of interaction between the wake and sleep states.

neuroscience↗

bioRxiv2023

Invariant relationship unites REM and NonREM sleep.

Establishing structural and functional links between two distinct types of sleep, rapid-eye-movement (REM) and non-REM (NREM), that alternate and form several sleep cycles per night, has posed a significant challenge. Here we demonstrate a simple invariant relationship where the product of the duration of NREM sleep episode and intensity of subsequent REM sleep episode remains constant over successive sleep cycles of normal human sleep. This Sleep Cycle Invariant (SCI), previously predicted by a quantitative model of sleep dynamics, supports the structural and functional unity of NREM and REM sleep. The significance of SCI for understanding normal sleep and sleep disorders is highlighted by alterations in REM sleep intensity and NREM sleep episode duration being a hallmark of major depression. One-Sentence SummaryThe duration of NREM sleep and intensity of REM sleep have an invariant relationship across normal sleep cycles of one night.

neuroscience↗