Spontaneous synchronization over large networks is ubiquitous in nature, ranging from inanimate to biological systems. In the human brain, neuronal synchronization and de-synchronization occur during sleep, with the greatest degree of neuronal synchronization during slow wave sleep (SWS). The current sleep classification schema is based on electroencephalography and provides common criteria for clinicians and researchers to describe stages of non-rapid eye movement (NREM) sleep as well as rapid eye movement (REM) sleep. These sleep stage classifications have been based on convenient heuristic criteria, with little consideration of the accompanying normal physiological changes across those same sleep stages. To begin to resolve those inconsistencies, first focusing only on NREM sleep, we propose a simple cluster synchronization model to explain the emergence of SWS in healthy people without sleep disorders. We apply the empirical mode decomposition (EMD) analysis to quantify slow wave activity in electroencephalograms, and provide quantitative evidence to support our model. Based on this synchronization model, NREM sleep can be classified as SWS and non-SWS, such that NREM sleep can be considered as an intrinsically bistable process. Finally, we develop an automated algorithm for SWS classification. We show that this new approach can unify brain wave dynamics and their corresponding physiologic changes.

Despite the increasing number of research studies of cardiopulmonary coupling (CPC) analysis, an electrocardiogram-based technique, the use of CPC in underserved population remains underexplored. This study aimed to first evaluate the reliability of CPC analysis for the detection of obstructive sleep apnea (OSA) by comparing with polysomnography (PSG)-derived sleep outcomes. Two hundred five PSG data (149 males, age 46.8 ± 12.8 years) were used for the evaluation of CPC regarding the detection of OSA. Automated CPC analyses were based on ECG signals only. Respiratory event index (REI) derived from CPC and apnea–hypopnea index (AHI) derived from PSG were compared for agreement tests. CPC-REI positively correlated with PSG-AHI (r = 0.851, p < 0.001). After adjusting for age and gender, CPC-REI and PSG-AHI were still significantly correlated (r = 0.840, p < 0.001). The overall results of sensitivity and specificity of CPC-REI were good. Compared with the gold standard PSG, CPC approach yielded acceptable results among OSA patients. ECG recording can be used for the screening or diagnosis of OSA in the general population.

Prior work has provided extensive documentation of threshold sensitivity and sensory hair cell losses after noise exposure. It is now clear, however, that cochlear synaptic loss precedes such losses, at least at low-moderate noise doses, silencing affected neurons. To address questions of whether, and how, cochlear synaptopathy and underlying mechanisms change as noise dose is varied, we assessed cochlear physiologic and histologic consequences of a range of exposures varied in duration from 15 min to 8 h and in level from 85 to 112 dB SPL. Exposures delivered to adult CBA/CaJ mice produced acute elevations in hair cell- and neural-based response thresholds ranging from trivial (similar to 5 dB) to large (similar to 50 dB), followed by varying degrees of recovery. Males appeared more noise vulnerable for some conditions of exposure. There was little to no inner hair cell (IHC) loss, but outer hair cell (OHC) loss could be substantial at highest frequencies for highest noise doses. Synapse loss was an early manifestation of noise injury and did not scale directly with either temporary or permanent threshold shift. With increasing noise dose, synapse loss grew to similar to 50%, then declined for exposures yielding permanent hair cell injury/loss. All synaptopathic, but no non-synaptopathic exposures produced persistent neural response amplitude declines; those additionally yielding permanent OHC injury/loss also produced persistent reductions in OHC-based responses and exaggerated neural amplitude declines. Findings show that widespread cochlear synaptopathy can be present with and without noise-induced sensory cell loss and that differing patterns of cellular injury influence synaptopathic outcomes. (C) 2019 IBRO. Published by Elsevier Ltd. All rights reserved.

Objective To evaluate the objective sleep status of patients with chronic insomnia by cardiopulmonary coupling (CPC) technique, and evaluate the characteristics of cognitive dysfunction to explore the correlation between objective sleep and cognitive dysfunction in patients with chronic insomnia. Methods Forty-three patients with chronic insomnia, admitted to our hospital from October 2017 to April 2019, were enrolled in our study;15 age-, gender-and education-matched healthy volunteers were recruited as control group. All subjects followed their daily routine at home and completed CPC examination. Montreal Cognitive Assessment (MoCA), Auditory Vocabulary Learning Test (AVLT), Trail Making Test (TMT) and Stroop Color Word Test were used to evaluate the general and single cognitive functions, respectively. The correlation of objective sleep with cognitive function was analyzed. Results (1) As compared with those in the control group, high frequency coupling (stable sleep) ratio was significantly decreased, low frequency coupling (un-stable sleep) ratio and extremely low frequency coupling (rapid-eye-movement sleep/waking) ratio were significantly increased, and latency of high frequency coupling was significantly prolonged in chronic insomnia group (P<0.05). (2) Chronic insomnia group had significantly lower MoCA total scores than control group (P<0.05), specifically manifested as decrement of visuospatial ability and execution and attention abilities; specific cognitive test showed that chronic insomnia group performed worse in immediate recall, and had delayed recall of AVLT, longer time consumption in TMT-B, smaller number of wired arrival numbers, and longer time consumption in Stroop color word test than the control group, with significant differences (P<0.05). (3) There was a correlation between CPC sleep structure and Cognitive Function Scale scores in patients with chronic insomnia. Conclusion In patients with chronic insomnia, stable sleep is reduced, un-stable sleep and rapid-eye-movement sleep/waking are increased; the impaired cognition domains are visual space and executive function, attention and memory; disturbed sleep structure aggravates the memory and execution impairment of patients with chronic insomnia.