Fundamentals of sleep regulation: Model and benchmark values for fractal and oscillatory neurodynamics

Bódizs, Róbert; Schneider, Bence; Ujma, Péter P.; Horváth, Csenge G.; Dresler, Martin; Rosenblum, Yevgenia

doi:10.1016/j.pneurobio.2024.102589

Cited by 4 publications

(3 citation statements)

References 232 publications

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“…Band- and binwise spectral analysis replicated experimental laboratory studies (Aeschbach and Borbély, 1993; Borbély et al, 1981; Marzano et al, 2010) and reveal that increased wakefulness results in increased NREM sleep PSD, most prominently at the lowest frequencies but extending up to the sigma range. Binwise statistics clearly revealed higher frequencies were progressively less involved in sleep homeostasis (Bódizs et al, 2024): effects transcend the canonical SWA range, extend over higher frequencies, but increasing EEG frequencies are characterized by decreasing sensitivity to extensions in pre-sleep wakefulness. Moreover, both the NREM sleep EEG spectral slope and exponents values increased as a function of time awake, supporting the relevance of these indices in depicting sleep homeostasis.…”

Section: Discussionmentioning

confidence: 99%

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Sleep homeostasis in a naturalistic setting

Ujma,

Bódizs

2024

Preprint

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Sleep, especially NREM sleep depth is homeostatically regulated, as sleep pressure builds up during wakefulness and diminishes during deep sleep. Previous evidence from this phenomenon, however, mainly stems from experimental studies which may not generalize to an ecologically valid setting. In the current study, we used a dataset of 246 individuals sleeping for at least seven nights each with a mobile EEG headband according to their ordinary daily schedule to investigate the effect of time spent in wakefulness on sleep characteristics. Increased time in wakefulness prior to sleep was associated with decreased sleep onset latency, increased sleep efficiency, a larger percentage of N3 sleep, and higher delta activity. Moreover, increased sleep pressure resulted in an increase in both the slope and the intercept of the sleep EEG spectrum. As predicted, PSD effects were most prominent in the earliest hours of sleep. Our results demonstrate that experimental findings showing increased sleep depth after extended wakefulness generalize to ecologically valid settings, and that time spent awake is an important determinant of sleep characteristics on the subsequent night. Our findings are evidence for the efficacy of sleep restriction, a behavioral technique already widely used in clinical settings, as a simple but powerful method to improve the objective quality of sleep in those with sleep problems.

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Section: Discussionmentioning

confidence: 99%

“…Recent evidence indicates a gradual levelling off of excess EEG power along the frequency scale, with lower frequencies showing stronger wake time-dependent upregulation. Consequently, sleep-wake history was best reflected by the steepness of the spectral slope of aperiodic activity in the sleep EEG (Bódizs et al, 2024).…”

Section: Introductionmentioning

confidence: 99%

Sleep homeostasis in a naturalistic setting

Ujma,

Bódizs

2024

Preprint

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“…Further, to provide a comprehensive quanti cation of broad-band electrophysiological slowing, we estimated the spectral exponent, which re ects the 1/f-like decay of the Power Spectral Density (PSD) and thus the relative contribution of high and low frequencies. Notably, the spectral exponent has been proven as a reliable index of consciousness across various physiological 32,33,34,35,36,37,38,39,40 pharmacological 41,42,43,44,45 and pathological conditions 18,42,44 , including states of disconnected consciousness. Crucially in the present context, the spectral exponent has been extensively validated in large pediatric samples to distinguish between wakefulness 46,47,48,49 and various sleep stages, including deep NREM sleep 35,46 .…”

Section: Introductionmentioning

confidence: 99%

Hemispherotomy: cortical islands of deep sleep in awake humans

Massimini,

Colombo

et al. 2024

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Hemispherotomy is a surgical procedure that disconnects a large portion of the cerebral cortex from cortical and subcortical inputs in patients with severe refractory epilepsy. Whether the disconnected cortex - inaccessible to behavioral assessment - supports consciousness remains unknown. Functional MRI studies have indicated preserved resting-state networks within the disconnected hemisphere, raising the possibility that it may represent an ‘island of awareness’. However, these networks can also persist in unconscious states, such as anesthesia and deep sleep. Here we assess the capacity of the disconnected cortex to support consciousness by exploring its electrophysiological state, before and after hemispherotomy, in ten awake pediatric patients. After surgery, the disconnected cortex–but not the contralateral cortex–entered a state dominated by slow oscillations (<2 Hz) resembling those observed during deep sleep; further, the spectral exponent, a previously validated marker of consciousness indexing the 1/f-like decay of the power spectral density, assumed values typically found in unconscious brain-injured and anesthetized adults. When compared to a reference pediatric sample, spectral exponent values were compatible with wakefulness in the contralateral cortex but attained levels typical of deep sleep over the disconnected cortex, suggesting that the disconnected cortex is not an island of awareness.

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Fractal cycles of sleep: a new aperiodic activity-based definition of sleep cycles

Rosenblum¹,

Esfahani

Adelhöfer

et al. 2023

Preprint

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Background: Textbooks define the classical sleep cycle as an episode of non-rapid eye movement (non-REM) sleep followed by an episode of REM sleep; sometimes, a REM episode can be "skipped". While sleep cycles are considered fundamental components of sleep, their functional significance remains to a large extent unclear. One of the reasons for a lack of research progress in the field is the absence of a data-driven definition. Here, we propose to reset the scientific definition of sleep cycles on fractal (aperiodic) neural activity as a well-established marker of arousal and sleep stages, arguing that this will considerably advance the field. Methods: We used electroencephalography to compute fractal slopes and explore their temporal dynamics over the course of nocturnal sleep. We defined the "fractal cycle of sleep" as a time interval during which fractal slopes descend from their local maximum to their local minimum and then lead back to the next local maximum. Next, we assessed the correspondence between the "fractal" and "classical" sleep cycles, including "skipped" cycles. Finally, we explored fractal cycles in childhood and adolescence, a life period with ongoing sleep architecture changes, as well as in major depressive disorder, a clinical condition characterized by disturbed sleep architecture. Results: Timings of "fractal" and "classical" cycles coincided in 763/940 (81%) cases and their durations (89±34 min vs 90±25 min) correlated positively (r=0.5, p<0.001). The fractal cycle algorithm detected "skipped" cycles in 53/55 (96%) cases. In adults (range: 18-75 years, n=205), the "fractal" cycle duration and participant's age correlated negatively (r=-0.2, p=0.006). Children and adolescents (range: 8-17 years, n=21) had shorter "fractal" cycles compared to young adults (range: 23-25 years, n=24) (mean: 76±34 vs 94±32 min, p<0.001). 38 unmedicated patients with depression showed shorter "fractal" cycles compared to their own medicated state (92±38 min vs 107±51 min, p<0.001). 111 medicated patients showed longer "fractal" cycles compared to 109 matched controls (104±49 vs 88±31 min, p<0.001). Conclusions: We show that "fractal cycles" are an objective, quantifiable and biologically plausible way to display sleep neural activity and its cycles, able to provide additional information compared to hypnograms. Likewise, "fractal cycles" can be used to study the effect of antidepressants on sleep.

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Fundamentals of sleep regulation: Model and benchmark values for fractal and oscillatory neurodynamics

Cited by 4 publications

References 232 publications

Sleep homeostasis in a naturalistic setting

Sleep homeostasis in a naturalistic setting

Hemispherotomy: cortical islands of deep sleep in awake humans

Fractal cycles of sleep: a new aperiodic activity-based definition of sleep cycles

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