The neural architecture of sleep regulation – insights from Drosophila

The neural mechanisms that balance waking and sleep to ensure adequate sleep quality in mammals are highly complex, often eluding functional insight. In the last two decades, researchers made impressive progress in studying the less complex brain of the invertebrate model organism Drosophila melanogaster, which has led to a deeper understanding of the neural principles of sleep regulation. Here, we will review these findings to illustrate that neural networks require sleep to undergo synaptic reorganization that allows for the incorporation of experiences made during the waking hours. Sleep need, therefore, can arise as a consequence of sensory processing, often signalized by neural networks as they synchronize their electrical patterns to generate slow-wave activity. The slow-wave activity provides the neurophysiological basis to establish a sensory gate that suppresses sensory processing to provide a resting phase which promotes synaptic rescaling and clearance of metabolites from the brain. Moreover, we demonstrate how neural networks for homeostatic and circadian sleep regulation interact to consolidate sleep into a specific daily period. We particularly highlight that the basic functions and physiological principles of sleep are highly conserved throughout the phylogenetic spectrum, allowing us to identify the functional components and neural interactions that construct the neural architecture of sleep regulation.

The deep and slow breathing characterizing rest favors brain respiratory-drive

A respiration-locked activity in the olfactory brain, mainly originating in the mechano-sensitivity of olfactory sensory neurons to air pressure, propagates from the olfactory bulb to the rest of the brain. Interestingly, changes in nasal airflow rate result in reorganization of olfactory bulb response. By leveraging spontaneous variations of respiratory dynamics during natural conditions, we investigated whether respiratory drive also varies with nasal airflow movements. We analyzed local field potential activity relative to respiratory signal in various brain regions during waking and sleep states. We found that respiration regime was state-specific, and that quiet waking was the only vigilance state during which all the recorded structures can be respiration-driven whatever the respiratory frequency. Using CO2-enriched air to alter respiratory regime associated to each state and a respiratory cycle based analysis, we evidenced that the large and strong brain drive observed during quiet waking was related to an optimal trade-off between depth and duration of inspiration in the respiratory pattern, characterizing this specific state. These results show for the first time that changes in respiration regime affect cortical dynamics and that the respiratory regime associated with rest is optimal for respiration to drive the brain.

Bedtimes, Bedtime Routines, and Children’s Sleep across the First Two Years of Life

Study Objectives The first objective of this study was to determine whether establishing bedtime routines in the first year of life predicts better sleep outcomes (i.e., longer sleep duration, less nighttime waking, earlier bedtime, shorter sleep latency, fewer sleep problems) across the first two years of life. The second objective was to determine whether specific adaptive bedtime activities (e.g., book reading) were associated with sleep outcomes. The third objective was to describe changes in adaptive bedtime activities (hug/kiss caregiver, say goodnight to family) across the first two years of life. Methods Parents of 468 children from the STRONG Kids 2 birth cohort were surveyed about bedtime and bedtime routines, their child’s sleep duration, nighttime waking, sleep latency and sleep problems at 3, 12, 18, and 24 months of age. Results Cross-lagged panel models revealed partial evidence for reciprocal associations between bedtime routine consistency and adaptive bedtime activities and better sleep outcomes over time. Specifically, more bedtime routine consistency predicted less nighttime waking and sleep problems, and more bedtime adaptive activities predicted longer sleep duration and fewer sleep problems. Discussion The findings are discussed from a developmental perspective to highlight how consistency of bedtime routines established as early as three months of age may affect sleep outcomes and that the adaptive activities associated with these routines may increase in frequency over the first two years of life.

Anatomical-Physiological and Biophysical Principles of Brain Functioning in Waking and Sleep

The analysis of some features of a brain work under condition of representation of a neocortex as set of cyclic neural circuits — cells of memory, has allowed understand many effects of a brain work. In particular the essence of a cognitive, creative activity, possible pathological conditions of memory: Alzheimer’s disease, etc. is investigated. Consideration of some other structures of a brain: hippocampus, entorhinal cortex has allowed understand a phenomenon of dream, its modes, essence of dreams, functionalities of a brain during dream, etc. Mathematical modelling of the electroencephalogram rhythms carried out during phases of slow dream. Interrelation of the rhythm’s frequency of slow dream with distance between the next cyclic neural circuits is shown.

The deep and slow breathing characterizing rest favors brain respiratory-drive

A respiration-locked activity in the olfactory brain, mainly originating in the mechano-sensitivity of olfactory sensory neurons to air pressure, propagates from the olfactory bulb to the rest of the brain. Interestingly, changes in nasal airflow rate result in reorganization of olfactory bulb response. Therefore, if the respiratory drive of the brain originates in nasal airflow movements, then it should vary with respiration dynamics that occur spontaneously during natural conditions. We took advantage of the spontaneous variations of respiration dynamics during the different waking and sleep states to explore respiratory drive in various brain regions. We analyzed their local field potential activity relative to respiratory signal. We showed that respiration regime was state-specific, and that quiet waking was the only vigilance state during which all the recorded structures can be respiration-driven whatever the respiration frequency. We used a CO2-enriched air to change the respiratory regime associated to each state and, using a respiratory cycle-by-cycle analysis, we evidenced that the large and strong brain entrainment during quiet waking was the consequence of its associated respiration regime consisting in an optimal trade-off between deepness and duration of inspiration. These results show for the first time that changes in respiration regime alter the cortical dynamics and that the respiratory regime associated with rest is optimal for respiration to drive the brain.

Multimodal imaging of sleep–wake disorders

While the neuroscience of sleep has traditionally been studied using electroencephalography (EEG), newer technologies have allowed for an enriched understanding of the brain’s ongoing activity during transitions into sleep, as well as during the distinct stages of sleep observed in humans. Neuroimaging techniques such as magnetic resonance imaging (MRI), functional MRI (fMRI), voxel-based morphometry (VBM), diffusion tensor imaging (DTI), magnetic resonance spectroscopy (MRS), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) allow researchers a window into the brain during both waking and sleep. As an extension, deviations from brain activity patterns observed in healthy good sleepers give clues to the specific brain abnormalities associated with disorders of sleep such as insomnia. This chapter will provide a selected overview of neuroimaging studies in sleep and sleep disorders.