Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep

Effects of one-night partial sleep deprivation on perivascular space volume fraction: Findings from the Stockholm Sleepy Brain Study

Increased waste clearance in the brain is thought to occur most readily during deep sleep (stage N3). Sleep deprivation disrupts time spent in deeper sleep stages, fragmenting the clearance process. Here, we have utilized the publicly available Stockholm Sleepy Brain Study to investigate whether various sleep-related measures are associated with changes in perivascular space (PVS) volume fraction following a late-night short-sleep experiment. The study sample consisted of 60 participants divided into old (65-75 years) and young (20-30 years) age groups. We found that partial sleep deprivation was not significantly associated with major PVS changes. In our centrum semiovale models, we observed an interaction between percentage of total sleep time spent in N3 and sleep deprivation status on PVS volume fraction. In our basal ganglia models, we saw an interaction between N2 (both percentage of total sleep time and absolute time in minutes) and sleep deprivation status. However, the significance of these findings did not survive multiple comparisons corrections. This work highlights the need for future longitudinal studies of PVS and sleep, allowing for quantification of within-subject morphological changes occurring in PVS due to patterns of poor sleep. Our findings here provide insight on the impact that a single night of late-night short-sleep has on the perivascular waste clearance system.

Glymphatic system dysfunction in adult ADHD: Relationship to cognitive performance

OBJECTIVES

While attention-deficit/hyperactivity disorder (ADHD) persists into adulthood, the relationship between glymphatic system function and cognitive performance in adult ADHD remains unclear. This study investigated the association between glymphatic system markers and cognitive outcomes in adults with ADHD.

METHODS

This case-control study includes 41 adults with ADHD and 108 age-matched healthy controls (HCs). Glymphatic function was evaluated using choroid plexus volume (CPV), diffusion tensor imaging along the perivascular space (DTI-ALPS) index and coupling between blood‑oxygen-level-dependent signals and cerebrospinal fluid signals (BOLD-CSF coupling). Cognitive performance was measured using standardized neuropsychological tests.

RESULTS

Compared with HCs, adults with ADHD exhibited significantly lower bilateral and whole-brain ALPS indices (P < 0.05). Although CPV was increased in the ADHD group, this difference did not reach statistical significance, and no significant differences were observed in BOLD-CSF coupling between the two groups. Furthermore, whole-brain ALPS indices were positively associated with visual memory performance (r = 0.422, P = 0.005), an effect that was more pronounced in the right hemisphere (r = 0.458, P = 0.002).

LIMITATIONS

The cross-sectional design limits causal inferences, and the effects of medication were not fully accounted for.

CONCLUSIONS

These findings identify an association between glymphatic dysfunction and cognitive impairment in adults with ADHD. The observed correlation suggests that alterations in glymphatic function may underlie ADHD-related cognitive deficits. Targeting these pathways could provide novel therapeutic opportunities in the management of adult ADHD.

Characterising the power spectrum dynamics of the non-REM to REM sleep transition

The transition from non-rapid eye movement (NREM) to rapid eye movement (REM) sleep is considered a transitional or intermediate stage (IS), characterised by high amplitude spindles in the frontal cortex and theta activity in the occipital cortex. Early reports in rats showed an IS lasting from 1 to 5 s, but recent studies suggested a longer duration of this stage of up to 20 s. To further characterise the IS, we analysed its spectral characteristics on electrocorticogram (ECoG) recordings of the olfactory bulb (OB), primary motor (M1), primary somatosensory (S1), and secondary visual cortex (V2) in 12 Wistar male adult rats. By comparing the IS with consolidated NREM/REM epochs, our results reveal that the IS has specific power spectral patterns that fall out of the NREM and REM sleep state power distribution. Specifically, the main findings were that sigma (11-16 Hz) power in OB, M1, S1, and V2 increased during the IS compared with NREM and REM sleep, which started first in the frontal part of the brain (OB -54 s, M1 -53 s) prior to the last spindle occurrence. The beta band (17-30 Hz) power showed a similar pattern to that of the sigma band, starting -54 s before the last spindle occurrence in the M1 cortex. Notably, sigma infraslow coupling (~0.02 Hz) increased during the IS but occurred at a slower frequency (~0.01 Hz) compared with NREM sleep. Thus, we argue that the NREM to REM transition contains its own local spectral profile, in accordance with previous reports, and is more extended than described previously.

Biological Fluid Flows: Signaling Mediums for Circadian Timing

While there is extensive literature on both the neuronal circuitry of rhythms and the intracellular molecular clock, there is a large component of signaling that has been understudied: interstitial fluid (ISF)-fluid that surrounds the cells in the extracellular space of tissue. In this review, we highlight evidence in the circadian literature supporting ISF signaling as key to circadian synchronization and entrainment and propose new mechanisms of how fluid movement between the brain and periphery may act as zeitgebers by examining the main ISF pathways of the body, focusing on circadian regulation of the glymphatic and lymphatic systems. We identify key pieces of circadian research that point to ISF as an important timing medium, expand on the basics of cerebrospinal fluid (CSF) and ISF production, and outline the basic structure and function of the glymphatic and lymphatic systems.

Neuronal oscillations in cognition: Down syndrome as a model of mouse to human translation

Down syndrome (DS), a prevalent cognitive disorder resulting from trisomy of human chromosome 21 (Hsa21), poses a significant global health concern. Affecting approximately 1 in 800 live births worldwide, DS is the leading genetic cause of intellectual disability and a major predisposing factor for early-onset Alzheimer's dementia. The estimated global population of individuals with DS is 6 million, with increasing prevalence due to advances in DS health care. Global efforts are dedicated to unraveling the mechanisms behind the varied clinical outcomes in DS. Recent studies on DS mouse models reveal disrupted neuronal circuits, providing insights into DS pathologies. Yet, translating these findings to humans faces challenges due to limited systematic electrophysiological analyses directly comparing human and mouse. Additionally, disparities in experimental procedures between the two species pose hurdles to successful translation. This review provides a concise overview of neuronal oscillations in human and rodent cognition. Focusing on recent DS mouse model studies, we highlight disruptions in associated brain function. We discuss various electrophysiological paradigms and suggest avenues for exploring molecular dysfunctions contributing to DS-related cognitive impairments. Deciphering neuronal oscillation intricacies holds promise for targeted therapies to alleviate cognitive disabilities in DS individuals.

A wireless device for continuous measurement of brain parenchymal resistance tracks glymphatic function in humans

Glymphatic function in animal models supports the clearance of brain proteins whose mis-aggregation is implicated in neurodegenerative conditions including Alzheimer's and Parkinson's disease. The measurement of glymphatic function in the human brain has been elusive due to invasive, bespoke and poorly time-resolved existing technologies. Here we describe a non-invasive multimodal device for the continuous measurement of sleep-active changes in parenchymal resistance in humans using repeated electrical impedance spectroscopy measurements in two separate clinical validation studies. Device measurements successfully paralleled sleep-associated changes in extracellular volume that regulate glymphatic function and predicted glymphatic solute exchange measured by contrast-enhanced MRI. We replicate preclinical findings showing that glymphatic function is increased with increasing sleep electroencephalogram (EEG) delta power and is decreased with increasing sleep EEG beta power and heart rate. The present investigational device permits the continuous and time-resolved assessment of parenchymal resistance in naturalistic settings necessary to determine the contribution of glymphatic impairment to risk and progression of Alzheimer's disease and to enable target-engagement studies that modulate glymphatic function in humans.

Harnessing the circadian nature of the choroid plexus and cerebrospinal fluid

Cerebrospinal fluid (CSF) exchanges with the central nervous system's immediate environment and interfaces with systemic circulation at the blood-CSF barrier. CSF composition reflects brain states, contributes to brain health and disease, is modulated by circadian rhythms and behaviors, and turns over multiple times per day, enabling rapid signal relay. Mechanisms of how CSF elements change over circadian time and influence function can be harnessed for diagnostic biomarkers and therapeutic intervention.

Sleuthing subjectivity: a review of covert measures of consciousness

Consciousness is private. Although conscious beings directly access their own conscious experiences, the consciousness of others must be inferred through overt report: observable behaviours - such as overt facial expressions, vocalizations and body gestures - that suggest the level, state and content of consciousness. However, overt report is limited because it can be erroneous (for example, resulting from wilful deception or being subject to recall error), absent (for example, during sleep and paralysis) or conflict with research goals (for example, in no-report paradigms and resting-state studies). These limitations encourage the search for covert measures of consciousness: physiological signals that disclose consciousness without relying on overt behaviour. This Review highlights emerging covert measures of consciousness in humans, including eye, skin, respiratory and heart signals. We also address the challenge of distinguishing physiological signals linked to conscious versus unconscious neural processing. Finally, we consider the ethical implications of infringing on the innate privacy of consciousness.

Research on recognition of bedding system coverage rate using infrared thermal imaging

This study investigated a new challenging problem: how to recognize bedding system coverage rate (BSCR) in real-time without contact. To overcome this problem, a method combining infrared thermal imaging with image segmentation algorithms was proposed. The infrared thermal images of 30 subjects with common coverage forms were captured under three shooting angles (45°, 60°, 90°) and three ambient temperatures (23 °C, 26 °C, 29 °C) to evaluate the effect of these factors on recognition accuracy. The proposed method was then applied in real-time to recognize BSCR in summer. And the subjective thermal perceptions (thermal sensation votes, thermal comfort votes) and objective sleep quality were collected. Three image segmentation methods were tested. And the K-means clustering excelled in recognizing BSCR, achieving an MAE of 3.70, RMSE of 4.67, and R2 of 0.901. The optimal shooting angle for infrared camera was 60°. Additionally, the summer indoor temperature (23 °C-29 °C) had no significant impact on the recognition accuracy. The average BSCR during sleep was 76.6 % under conditions of thermal comfort and good sleep quality. Notably, females exhibited the BSCR that was 8.9 % higher than that of males (p < 0.01). This study provides reference data and insights for establishing a non-contact sleep thermal comfort prediction model.

Using PINS pulses to saturate inflow effects on fMRI data at 3 and 7 T

PURPOSE

To suppress inflow effects by saturating the magnetization within slice gaps.

METHODS

Power independent of number of slices (PINS) pulses was designed to saturate the magnetization in all slice gaps at once. The PINS saturation module was played before every excitation. The saturation and excitation profiles were validated in simulation and phantom experiments. To demonstrate the efficacy of the method to suppress inflow, experiments were performed using a flow phantom. As an example use-case, fMRI experiments with and without PINS inflow saturation were performed at 3 T and 7 T.

RESULTS

Simulations and phantom experiments showed that the PINS saturation module successfully saturated the magnetization in the slice gaps without degrading the slice profile of the imaging slices. Flow phantom experiments showed that the PINS saturation module suppresses through-plane inflow better than no-gap acquisitions. In vivo fMRI experiments demonstrated that the PINS saturation module can be used to modulate the spin-echo BOLD signal. At 3 T application of PINS pulses to saturate the magnetization in the slice gaps resulted in approximately 25% fewer activated voxels (PINS-ON vs. PINS-OFF). Interestingly, at 7 T the activation patterns remained more similar and only approximately 10% fewer activated voxels were detected. The observed difference between 3 and 7 T may be linked to the relative shortening of the blood T2.

CONCLUSION

Using PINS pulses, inflow effects from slice gaps were effectively and efficiently saturated. The proposed PINS saturation module can be used to further study the contribution of inflow effects in fMRI data.

Reduced glymphatic clearance in early psychosis

Psychosis involves neuroinflammation and oxidative stress, both affecting the glymphatic system, the lymphatic-like, fluid-transport system in the brain. However, it is unclear whether early psychosis is related to impairments in glymphatic functions. In resting-state fMRI, it has been recently established in a number of neurodegenerative diseases that the coupling relationship between cortical blood-oxygen-level-dependent (BOLD) signal and ventricular cerebrospinal fluid (CSF) flow is associated with brain waste clearance, a key glymphatic function that has not been examined in psychosis or any other psychiatric populations. In a large dataset (total n = 137, age = 23.86 ± 4.16), we demonstrated that glymphatic clearance marked by BOLD-CSF coupling was weaker and more delayed in patients with early psychosis compared to healthy controls. BOLD-CSF coupling also varied between the non-affective and affective psychosis groups with group differences most prominent in high-order but not low-order cortical regions. Finally, reduced global BOLD-CSF coupling was associated with cognitive decline and more severe psychotic symptoms. We provided novel evidence highlighting dysregulated coupling between cortical activity and macroscopic CSF flow as a biomarker for early psychosis. Similar to recent observations in neurodegenerative disorders, the association between reduced BOLD-CSF coupling and psychotic symptoms suggested that waste clearance is disrupted in psychosis which shed light on the pathophysiology of this disease from a glymphatic point of view.

Amplitude fluctuations of cerebrovascular oscillations and CSF movement desynchronize during NREM3 sleep

Fluctuations in cerebral blood volume (CBV) are a dominant mechanism aiding cerebrospinal fluid (CSF) movement in the brain during wakefulness and non-rapid eye movement (NREM) sleep. However, it is unclear if the amplitudes of CBV oscillations also change in proportion to the changes in amplitude of CSF movement across specific NREM sleep states. It is also not known if the coupling strength between them varies between NREM sleep states. To investigate these relationships, we measured cerebral hemodynamics and craniad CSF movement at the fourth ventricle simultaneously during wakefulness and NREM sleep states using concurrent Electroencephalography and functional Magnetic Resonance Imaging. We found that the amplitude fluctuations of cerebral hemodynamics and CSF oscillations desynchronize from one another only during deep NREM3 state, despite the strong mechanical coupling between CBV changes and CSF movement, which was consistent across all states. This suggests the existence of a different mechanism, linked to the cortical interstitial volume/resistance change, that regulates the NREM3 CSF inflow into the brain.

Glymphatics and meningeal lymphatics unlock the brain-immune code

The central nervous system (CNS) was once perceived as entirely shielded from the immune system, protected behind the blood-brain barrier and thought to lack lymphatic drainage. However, recent evidence has challenged many dogmas in neuroimmunology. Indeed, by means of glymphatics, brain-derived "waste" from deep within the CNS mobilizes toward immunologically active brain borders, where meningeal lymphatic vessels are appropriately positioned to drain antigens from the brain to the periphery. Accordingly, the presentation of brain-derived self-peptides emerges at the brain's borders and drives T cell responses with suppressive properties, critical in allowing active immunosurveillance while limiting aberrant immune reactivity. Taking into consideration these concepts, we further discuss how inflammation, aging, and neurodegenerative diseases potentially reshape the repertoire of self-antigens and immune cells, disrupting the healthy dialogue between the CNS and immune system. Collectively, this evolving perspective unveils new therapeutic avenues for CNS pathologies.

Cerebral small vessel disease: The impact of glymphopathy and sleep disorders

The glymphatic system, a vital brain perivascular network for waste clearance, hinges on the functionality of the aquaporin 4 (AQP4) water channel. Alarmingly, AQP4 single nucleotide polymorphisms (SNPs) are linked to impaired glymphatic clearance, or glymphopathy, which contributes to sleep disturbances and various age-related neurodegenerative diseases. Despite the critical role of glymphopathy and sleep disturbances in cerebral small vessel disease (CSVD) - a silent precursor to age-related neurodegenerative disorders - their interplay remains underexplored. CSVD is a major cause of stroke and dementia, yet its pathogenesis is not fully understood. Emerging evidence implicates glymphopathy and sleep disorders as pivotal factors in age-related CSVD, exacerbating the condition by hindering waste removal and compromising blood-brain barrier (BBB) integrity. Advanced imaging techniques promise to enhance diagnosis and monitoring, while lifestyle modifications and personalised medicine present promising treatment avenues. This narrative review underscores the need for a multidisciplinary approach to understanding glymphopathy and sleep disorders in CSVD. By exploring their roles, emphasising the necessity for longitudinal studies, and discussing potential therapeutic interventions, this paper aims to pave the way for new research and therapeutic directions in CSVD management.

MR Imaging of Neurofluids in the Developing Brain

The different fluid compartments in the developing brain work together to facilitate the delivery of nutrients, neurotransmitters, and neuromodulators. The cerebrospinal fluid and interstitial fluid are essential for clearing macromolecules from the brain, a process that involves the recently discovered meningeal lymphatics. Disruptions in these interactions can hinder normal brain development. Additionally, alterations in systemic fluid dynamics may contribute to neurologic complications, highlighting the need for a more holistic approach to understanding and treating neurologic diseases. MR imaging techniques show potential for detecting these pathologic processes in pediatric neurologic disorders.

Targeting Sleep Physiology to Modulate Glymphatic Brain Clearance

Sleep has been postulated to play an important role in the removal of potentially neurotoxic molecules, such as amyloid-β, from the brain via the glymphatic system. Disturbed sleep, on the other hand, may contribute to the accumulation of neurotoxins in brain tissue, eventually leading to neuronal death. A bidirectional relationship has been proposed between impaired sleep and neurodegenerative processes, which start years before the onset of clinical symptoms associated with conditions like Alzheimer's and Parkinson's diseases. Given the heavy burden these conditions place on society, it is imperative to develop interventions that promote efficient brain clearance, thereby potentially aiding in the prevention or slowing of neurodegeneration. In this review, we explore whether the metabolic clearance function of sleep can be enhanced through sensory (e.g., auditory, vestibular) or transcranial (e.g., magnetic, ultrasound, infrared light) stimulation, as well as pharmacological (e.g., antiepileptics) and behavioral (e.g., sleeping position, physical exercise, cognitive intervention) modulation of sleep physiology. A particular focus is placed on strategies to enhance slow-wave activity during nonrapid eye movement sleep as a driver of glymphatic brain clearance. Overall, this review provides a comprehensive overview on the potential preventative and therapeutic applications of sleep interventions in combating neurodegeneration, cognitive decline, and dementia.

PET Imaging of Neurofluids

Following a brief review of brain neurofluid pathways and the general PET technique, we introduce PET imaging of cerebrospinal fluid and interstitial fluid dynamics. Our summary includes both our published and unpublished observations on the modeling of PET imaging for neurofluid quantification in aging, Alzheimer's disease, and in the presence of amyloid lesions. We identify the limitations of PET imaging and point to validations and potential future directions.

U-Net-Based Prediction of Cerebrospinal Fluid Distribution and Ventricular Reflux Grading

Previous work indicates evidence that cerebrospinal fluid (CSF) plays a crucial role in brain waste clearance processes and that altered flow patterns are associated with various diseases of the central nervous system. In this study, we investigate the potential of deep learning to predict the distribution in human brain of a gadolinium-based CSF contrast agent (tracer) administered intrathecal. For this, T1-weighted magnetic resonance imaging (MRI) scans taken at multiple time points before and after injection were utilized. We propose a U-net-based supervised learning model to predict pixel-wise signal increase at its peak after 24 h. Performance is evaluated based on different tracer distribution stages provided during training, including predictions from baseline scans taken before injection. Our findings show that training with imaging data from only the first 2-h postinjection yields tracer flow predictions comparable to models trained with additional later-stage scans. Validation against ventricular reflux gradings from neuroradiologists confirmed alignment with expert evaluations. These results demonstrate that deep learning-based methods for CSF flow prediction deserve more attention, as minimizing MR imaging without compromising clinical analysis could enhance efficiency, improve patient well-being and lower healthcare costs.

Decoupling of global signal and cerebrospinal fluid inflow is associated with cognitive decline in patients with obstructive sleep apnoea

OBJECTIVES

The role of cortical glymphatic dysfunction in the cognitive impairment of the obstructive sleep apnea (OSA) requires further study. To compare the coupling between the resting-state blood-oxygen-level-dependent (BOLD) signals and cerebrospinal fluid (CSF) signals (BOLD-CSF coupling), a proxy for the cortical glymphatic function, across patients with differing severities of OSA and relate them with disease characteristics and treatment.

METHODS

A total of 153 participants (89 OSA patients and 64 matched controls) were prospectively included. OSA patients were classified into three groups (mild, moderate, and severe OSA) according to the apnea-hypopnea index (AHI). All participants underwent neuropsychological assessment and BOLD functional magnetic resonance imaging. BOLD-CSF coupling was assessed at global and regional levels and correlated with the cognitive impairment. Alterations in BOLD-CSF coupling and cognitive performance after treatment were assessed in OSA patients.

RESULT

Severe OSA patients exhibited weaker global and anterior BOLD-CSF coupling than mild OSA patients, moderate OSA patients, and healthy controls (HCs). Furthermore, the weaker global and anterior BOLD-CSF coupling was associated with poor cognitive performance in all OSA patients. Notably, cognitive performance and cortical glymphatic function improved significantly in patients with OSA after treatment.

CONCLUSION

Our findings demonstrated cortical glymphatic dysfunction in severe OSA patients, especially in the anterior region of the brain. Cortical glymphatic dysfunction may underlie the cognitive impairment in OSA patients, both of which would improve in OSA patients after treatment.

Simultaneous measurement of cerebral blood flow and cerebrospinal fluid flow using pseudo-continuous arterial spin labeling

In the brain clearance system, the movement of cerebrospinal fluid (CSF) plays a key role in processing waste products. Previous studies have shown that CSF flow interacts significantly with cerebral blood flow (CBF) during brain waste clearance, but there are no simultaneous measurements and comparisons of these two metrics in humans. This study introduces a novel method for simultaneously measuring CSF pulsatile movement and CBF using pseudo-continuous arterial spin labeling (pCASL) MRI. We conducted a comparative analysis of the correlation between CBF and CSF pulsatile movement in human subjects during breath-holding and motor task conditions. Our findings demonstrate the effectiveness of our proposed technique in measuring CSF pulsatile movement, as validated by comparing results with phase-contrast MRI at corresponding locations. Importantly, we observed a robust positive correlation between CBF and CSF pulsation concurrently measured through pCASL during breath-holding. Furthermore, through inter-subject comparisons of regional CBF and CSF pulsation, we established that higher blood perfusion in putamen, caudate, and pallidum regions, which are included in basal ganglia structure, corresponds to greater CSF pulsatile movement. Our motor tasks significantly increased CBF in the motor cortex, and CSF pulsation measured in the dorsal part around cisterna magna showed a decreasing tendency in the motor condition compared to the resting state, aligning with the Monroe-Kelly doctrine. Accordingly, these results demonstrate the feasibility of simultaneous measurement of CBF and CSF pulsation using the proposed pCASL technique in humans, which warrants further investigation.

Fast fluid-attenuated T2 mapping via multiple overlapping-echo detachment acquisition enhances preoperative histological classification of meningiomas

Fluid-attenuated inversion recovery (FLAIR) is indispensable in MRI-based head-and-neck assessments, but its quantitative counterpart remains clinically absent due to the influence of cerebrospinal fluid (CSF) dynamics and the lengthy acquisition time spent on a series of weighting-increasing images. This work implements and validates fast fluid-attenuated T2 (FLA-T2) mapping via inversion-recovery-prepared multiple overlapping-echo detachment imaging (IR-MOLED). The clinical value is prospectively investigated with a cohort of 54 meningioma patients (mean age: 56 years ± 11 [standard deviation]; 19 men). Fluid-attenuated proton density mapping was simultaneously fulfilled and therefore intrinsically co-registered, revealing notable benefits in identifying CSF inflow. In quantifying parenchymal T2, IR-MOLED yielded a mean absolute error of 1.22 ms referring to spin-echo, and in fluid suppression, IR-MOLED exhibited a high radiographic consistence with orthodox FLAIR imaging. Using first-level histogram analysis, results of meningioma investigation first discovered: (1) in grading meningiomas, FLA-T2 mapping (AUC = 0.814) outshined FLAIR imaging (AUC = 0.685), contrast-enhanced T1-weighted imaging (insignificant), and T2 mapping (insignificant); and (2) in typing meningiomas, FLA-T2 classified transitional meningiomas from meningothelial or/and fibrous meningiomas, complementing the predictive ability of T2 mapping. In conclusion, with excluded parametric contribution from free water and standardized voxel value scales, FLA-T2 mapping permits a more precise description of brain parenchyma in both structural morphology and relaxation variables than T2 mapping and is fully superior to FLAIR imaging in preoperatively predicting the histopathologic heterogeneity of meningiomas.

Diffusion Tensor Imaging in Neurofluids

In this review article, we describe the development and application of diffusion-based MR imaging methods for studying glymphatic physiology. Fluid exchange and solute transport are the 2 key components of the glymphatic system. Here we describe the use of low b-value imaging, free water fraction imaging, and diffusion time sensitization to leverage cerebral spinal fluid, as well as interstitial fluid motion in the parenchyma. We also describe multiple b-value diffusion imaging to better delineate diffusion components within the brain. Finally, we touch upon newer approaches that use advanced models of the diffusion signal, including high b-value imaging.

Brain physiological pulsations are linked to sleep architecture and cognitive performance in older adults

BACKGROUND

The glymphatic system facilitates efficient waste clearance in the brain through the movement of cerebrospinal fluid (CSF) along perivascular spaces. Animal studies have demonstrated that glymphatic efficiency declines with age, but evidence for such decline in humans is limited. We hypothesized that reduced glymphatic efficiency in older adults may be related to age-related worsening of sleep quality, potentially contributing to cognitive impairment.

METHODS

20 participants aged ≥60 years provided multi-dimensional cognitive measures, overnight polysomnography, and Magnetic Resonance Encephalography (MREG) performed the morning following the PSG. MREG is a single-shot, three-dimensional (3D) sequence employing a spherical stack-of-spirals trajectory that undersamples 3D k-space, enabling whole-brain data acquisition every 100 milliseconds to non-invasively and dynamically assess brain physiological pulsations. Spectral power and optical flow analyses quantified physiological pulsations within cardiovascular (CvB; 0.52-1.6 Hz), respiratory (RFB; 0.11-0.44 Hz), and low-frequency (LFB; 0.008-0.1 Hz) bands. These measures were correlated with cognitive test scores and sleep parameters assessed by overnight polysomnography.

RESULTS

Significant associations emerged between physiological pulsations, sleep, and cognitive measures. Cardiovascular pulsation strength correlated with non-rapid eye movement (NREM) stage 3 (N3) sleep percentage (peak voxel in right frontal pole; r = 0.72, p < 0.001) and language domain performance (left calcarine gyrus; r = 0.56, p = 0.01). Respiratory pulsations correlated strongly with sleep onset latency (right inferior temporal gyrus; r = 0.75, p < 0.001). Additionally, low-frequency pulsations were associated with sleep onset latency (right precentral gyrus; r = 0.67, p = 0.002). These findings suggest that glymphatic efficiency, as reflected by brain pulsations, is closely linked to sleep quality and cognitive performance in older adults, particularly involving cortical and subcortical structures relevant to cognitive and sleep regulatory functions.

CONCLUSION

This study uniquely demonstrates that brain physiological pulsations measured non-invasively with MREG are significantly associated with sleep architecture and cognitive performance in older adults. These findings underscore the potential of MREG to assess glymphatic function and provide important insights into the mechanisms linking sleep disturbances, cognitive decline, and aging. The identified correlations between pulsations and specific brain regions highlight potential pathways through which impaired glymphatic function could contribute to cognitive decline in older adults, suggesting promising avenues for future clinical and research applications.

Modeling dynamic inflow effects in fMRI to quantify cerebrospinal fluid flow

Cerebrospinal fluid (CSF) flow in the brain is tightly regulated and essential for brain health, and imaging techniques are needed to quantitatively establish the properties of this flow system. Flow-sensitive fMRI has recently emerged as a tool to measure large scale CSF flow dynamics with high sensitivity and temporal resolution; however, the measured signal is not quantitative. Here, we developed a dynamic model to simulate fMRI inflow signals based on time-varying flow velocities. We validated the model in both human and phantom data, and used it to identify important properties of the fMRI inflow signal that inform how the signal should be interpreted. Additionally, we developed a physics-based deep learning framework to invert the model, which enables direct estimation of velocity using fMRI inflow data. This work allows new quantitative information to be obtained from fMRI, which will enable neuroimaging researchers to take advantage of the high sensitivity, high temporal resolution, and wide availability of fMRI to obtain flow signals that are physically interpretable.

The Interplay Between the Sleep Slow Oscillation and Cerebrospinal Fluid: New Vistas for Insomnia Research

Insomnia disorder affects about 10% of the global population, representing a major health concern. Despite the availability of evidence-based treatments, the neurobiological mechanisms underpinning this disorder remain poorly understood. Recently, the investigation of the less than 1 Hz oscillations (commonly termed slow oscillations), a hallmark of slow wave sleep, has gained increased interest in research on insomnia. In this context, an intriguing perspective arises from the association between slow oscillations and metabolic waste clearance, an impaired process in individuals suffering from insomnia disorder. Indeed, the exploration of the relationships between cerebrospinal fluid dynamics and glymphatic system functions, which relate to brain metabolic clearance, and sleep slow oscillations may represent a promising avenue for future research in this field. This narrative review examines current knowledge about the intricate interplay among these mechanisms and their implications for insomnia disorder. Particular attention is given to the role of sleep slow oscillations in the clearance of metabolic waste during sleep, their coupling with cerebrospinal fluid oscillations, and the regulatory mechanisms underlying glymphatic function. The review emphasises the relevance of investigating sleep slow oscillations-related mechanisms in insomnia, intending to provide novel insights into the neurophysiological underpinnings of the disorder and contribute to more accurate diagnostic approaches. Furthermore, a deeper understanding of these mechanisms could pave the way for the development of innovative or adjunctive therapeutic strategies targeting sleep slow oscillations-related alterations in insomnia disorder.

Glymphatic function and choroid plexus volume is associated with systemic inflammation and oxidative stress in major depressive disorder

BACKGROUND

Inflammatory processes were recognized as key factors in the pathophysiology of major depressive disorder (MDD). The choroid plexus (ChP) and glymphatic system played central roles in immune interactions between the brain and periphery. However, their specific roles in MDD and their relationship with systemic inflammation and oxidative stress remained unclear.

METHODS

This study finally included 665 MDD patients and 338 healthy controls. Clinical data and MRI scans were collected, and some patients also underwent blood routine and biochemical tests. ChP volume was manually segmented, and the diffusion tensor imaging along the perivascular space (DTI-ALPS) index, reflecting glymphatic function, was obtained through the FSL pipeline. The differences in these dices between groups were compared, and their associations with systemic inflammation and oxidative stress were analyzed.

RESULTS

MDD patients showed increased ChP volume (total: d = 0.316, p < 0.001; left: d = 0.317, p < 0.001; right: d = 0.268, p = 0.003) and decreased DTI-ALPS index (d = -0.144, p = 0.022), with a negative correlation between them (ρ = -0.135, p < 0.001). In MDD patients, lower DTI-ALPS index was correlated with higher LHR (ρ = -0.107, p = 0.025) and MHR (ρ = -0.126, p = 0.008). Larger right ChP volume was associated with higher MLR (ρ = 0.107, p = 0.009), SIRI (ρ = 0.086, p = 0.036), PIV (ρ = 0.086, p = 0.036), MHR (ρ = 0.136, p = 0.004), and PHR (ρ = 0.126, p = 0.008), while larger total ChP volume was correlated with higher MHR (ρ = 0.097, p = 0.042) and PHR (ρ = 0.114, p = 0.017).

CONCLUSION

MDD appeared to be accompanied by an increase in ChP volume and a decrease in glymphatic function, and these changes were related to systemic inflammation and oxidative stress.

Nocturnal short-term heart rate variability reflects impaired daytime vigilance better than overnight heart rate variability in suspected obstructive sleep apnea patients

In obstructive sleep apnea (OSA), heart rate variability (HRV) decreases and performance in psychomotor vigilance task (PVT) worsens with more severe hypoxic load. Nevertheless, the association between HRV and PVT performance is poorly understood. Thus, we hypothesize that nocturnal short-term HRV is better related to daytime psychomotor vigilance compared with overnight HRV. To investigate this hypothesis, we retrospectively analyzed the electrocardiograms from polysomnographies of 546 consecutive patients with suspected OSA. We determined overnight HRV and short-term HRV in nonoverlapping 5-min segments and performed stepwise linear regression analyses to associate HRV with the median reaction time (RT) in the PVT. The short-term decrease in the median interval between two successive normal R peaks (NN interval), root mean square of successive NNs, and normalized high-frequency band power were all significant (p < 0.001) indicators of longer median RTs. However, the overnight HRV parameters did not indicate worsening median RT. Instead, increased hypoxic load and N3 duration were associated with longer median RT in men but not in women. The association of HRV and cardiorespiratory coupling with PVT performance was generally weak. Nocturnal short-term HRV evaluation reflected a state of vigilance better than the average overnight HRV. Thus, the overnight HRV analysis might not be optimal for patients with OSA. Utilizing the HRV analysis in a time-series manner and combined with the hypoxic load and sleep stages could bring new aspects to the health assessment of patients with OSA.

A time window for memory consolidation during NREM sleep revealed by cAMP oscillation

Memory formation requires specific neural activity in coordination with intracellular signaling mediated by second messengers such as cyclic adenosine monophosphate (cAMP). However, the real-time dynamics of cAMP remain largely unknown. Here, using a genetically encoded cAMP sensor with high temporal resolution, we found neural-activity-dependent rapid cAMP elevation during learning. Interestingly, in slow-wave sleep, during which memory consolidation occurs, the cAMP level in mice was anti-correlated with neural activity and exhibited norepinephrine β1 receptor-dependent infra-slow oscillations that were synchronized across the hippocampus and cortex. Furthermore, the hippocampal-cortical interactions increased during the narrow time-window of the peak cAMP level; suppressing hippocampal activity specifically during this window impaired spatial memory consolidation. Thus, hippocampal-dependent memory consolidation occurs within a specific time window of high cAMP activity during slow-wave sleep.

Extracellular vesicles as precision therapeutics for psychiatric conditions: targeting interactions among neuronal, glial, and immune networks

The critical role of the immune system in brain function and dysfunction is well recognized, yet development of immune therapies for psychiatric diseases has been slow due to concerns about iatrogenic immune deficiencies. These concerns are emphasized by the lack of objective diagnostic tools in psychiatry. A promise to resolve this conundrum lies in the exploitation of extracellular vesicles (EVs) that are physiologically produced or can be synthetized. EVs regulate recipient cell functions and offer potential for EVs-based therapies. Intranasal EVs administration enables the targeting of specific brain regions and functions, thereby facilitating the design of precise treatments for psychiatric diseases. The development of such therapies requires navigating four dynamically interacting networks: neuronal, glial, immune, and EVs. These networks are profoundly influenced by brain fluid distribution. They are crucial for homeostasis, cellular functions, and intercellular communication. Fluid abnormalities, like edema or altered cerebrospinal fluid (CSF) dynamics, disrupt these networks, thereby negatively impacting brain health. A deeper understanding of the above-mentioned four dynamically interacting networks is vital for creating diagnostic biomarker panels to identify distinct patient subsets with similar neuro-behavioral symptoms. Testing the functional pathways of these biomarkers could lead to new therapeutic tools. Regulatory approval will depend on robust preclinical data reflecting progress in these interdisciplinary areas, which could pave the way for the design of innovative and precise treatments. Highly collaborative interdisciplinary teams will be needed to achieve these ambitious goals.

Pitolisant alleviates brain network dysfunction and cognitive deficits in a mouse model of Alzheimer's disease

Histamine H3 receptor (H3R) antagonists regulate histamine release that modulates neuronal activity and cognitive function. Although H3R is elevated in Alzheimer's disease (AD) patients, whether H3R antagonists can rescue AD-associated neural impairments and cognitive deficits remains unknown. Pitolisant is a clinically approved H3R antagonist/inverse agonist that treats narcolepsy. Here, we find that pitolisant reverses AD-like pathophysiology and cognitive impairments in an AD mouse model. Behavioral assays and in vivo wide-field Ca2+ imaging revealed that recognition memory, learning flexibility, and slow-wave impairment were all improved following the 15-day pitolisant treatment. Improved recognition memory was tightly correlated with slow-wave coherence, suggesting slow waves serve as a biomarker for treatment response and for AD drug screening. Furthermore, pitolisant reduced amyloid-β deposition and dystrophic neurites surrounding plaques, and enhanced neuronal lysosomal activity, inhibiting which blocked cognitive and slow-wave restoration. Our findings identify pitolisant as a potential therapeutic agent for AD treatments.

The pulsing brain: state of the art and an interdisciplinary perspective

Understanding the pulsing dynamics of tissue and fluids in the intracranial environment is an evolving research theme aimed at gaining new insights into brain physiology and disease progression. This article provides an overview of related research in magnetic resonance imaging, ultrasound medical diagnostics and mathematical modelling of biological tissues and fluids. It highlights recent developments, illustrates current research goals and emphasizes the importance of collaboration between these fields.

Simultaneous coherent-incoherent motion imaging in brain parenchyma

A phase-sensitive diffusion tensor magnetic resonance imaging (MRI) sequence is proposed with pulse timing optimization scheme to achieve velocity resolution of less than 20 μm s-1 and an integrated image reconstruction and velocity map generation pipeline. The application of ultra-slow flow relevant to neurofluids is enabled by the use of a recently developed, ultra-high-performance brain MRI gradient system. By simultaneously reconstructing magnitude and phase data, both metrics that characterize diffusive fluid motion and coherent velocity maps are calculated non-invasively in human subjects, time-resolved over the entire cardiac cycle. The resulting acquisition and reconstruction of velocity maps in brain parenchyma, enabled by high-performance brain imaging systems, promises to be an important approach to investigating ultra-slow neurofluid flow and glymphatic circulation.

Assessing the feasibility of a new approach to measure the full spectrum of cerebrospinal fluid dynamics within the human brain using MRI: insights from a simulation study

Cerebrospinal fluid (CSF) dynamics are essential in the waste clearance of the brain. Disruptions in CSF flow are linked to various neurological conditions, highlighting the need for accurate measurement of its dynamics. Current methods typically capture high-speed CSF movements or focus on a single-frequency component, presenting challenges for comprehensive analysis. This study proposes a novel approach using displacement encoding with stimulated echoes (DENSE) MRI to assess the full spectrum of CSF motion within the brain. Through simulations, we evaluated the feasibility of disentangling distinct CSF motion components, including heartbeat- and respiration-driven flows, as well as a net velocity component due to continuous CSF turnover, and tested the performance of our method under incorrect assumptions about the underlying model of CSF motion. Results demonstrate that DENSE MRI can accurately separate these components, and reliably estimate a net velocity, even when periodic physiological motions vary over time. The method proved to be robust for including low-frequency components, incorrect assumptions on the nature of the net velocity component and missing CSF components in the model. This approach offers a comprehensive measurement technique for quantifying CSF dynamics, advancing our understanding of the relative role of various drivers of CSF dynamics in brain clearance.

Sleep Alterations and Cognitive Decline

Sleep disturbances and cognitive decline are intricately connected, and both are prevalent in aging populations and individuals with neurodegenerative disorders such as Alzheimer's disease (AD) and other dementias. Sleep is vital for cognitive functions including memory consolidation, executive function, and attention. Disruption in these processes is associated with cognitive decline, although causal evidence is mixed. This review delves into the bidirectional relationship between alterations in sleep and cognitive impairment, exploring key mechanisms such as amyloid-β accumulation, tau pathology, synaptic homeostasis, neurotransmitter dysregulation, oxidative stress, and vascular contributions. Evidence from both experimental research and population-based studies underscores the necessity of early interventions targeting sleep to mitigate risks of neurodegenerative diseases. A deeper understanding of the interplay between sleep and cognitive health may pave the way for innovative strategies to prevent or reduce cognitive decline through improved sleep management.

Sleep abnormalities are associated with greater cognitive deficits and disease activity in Huntington's disease: a 12-year polysomnographic study

Increasing evidence suggests that the sleep pathology associated with neurodegenerative diseases can in turn exacerbate both the cognitive deficits and underlying pathobiology of these conditions. Treating sleep may therefore bear significant, even disease-modifying, potential for these conditions, but how best and when to do so remains undetermined. Huntington's disease, by virtue of being an autosomal dominant neurodegenerative disease presenting in mid-life, presents a key 'model' condition through which to advance this field. To date, however, there has been no clinical longitudinal study of sleep abnormalities in Huntington's disease and no robust interrogation of their association with disease onset, cognitive deficits and markers of disease activity. Here, we present the first such study. Huntington's disease gene carriers (n = 28) and age- and sex-matched controls (n = 21) were studied at baseline and 10- and 12-year follow-up. All Huntington's disease gene carriers were premanifest at baseline and were stratified at follow-up into 'prodromal/manifest' versus 'premanifest' groups. Objective sleep abnormalities were assessed through two-night inpatient polysomnography and 2-week domiciliary actigraphy, and their association was explored against Montreal Cognitive Assessment, Trail A/B task, Symbol Digit Modalities Task (SDMT), Hopkins Verbal Learning Task (HVLT) and Montgomery-Asberg Depression Rating Scale (MADRS) scores, plus serum neurofilament light levels. Statistical analysis incorporated cross-sectional ANOVA, longitudinal repeated measures linear models and regressions adjusted for multiple confounders including disease stage. Fifteen Huntington's disease gene carriers phenoconverted to prodromal/early manifest Huntington's disease by study completion. At follow-up, these gene carriers showed more frequent sleep stage changes (P ≤ 0.001, ηp 2 = 0.62) and higher levels of sleep maintenance insomnia (defined by wake after sleep onset, P = 0.002, ηp 2 = 0.52). The latter finding was corroborated by nocturnal motor activity patterns on follow-up actigraphy (P = 0.004, ηp 2 = 0.32). Greater sleep maintenance insomnia was associated with greater cognitive deficits (Trail A P ≤ 0.001, R 2 = 0.78; SDMT P = 0.008, R 2 = 0.63; Trail B P = 0.013, R 2 = 0.60) and higher levels of neurofilament light (P = 0.015, R 2 = 0.39). Longitudinal modelling suggested that sleep stage instability accrues from the early premanifest phase, whereas sleep maintenance insomnia emerges closer to phenoconversion. Baseline sleep stage instability was able to discriminate those who phenoconverted within the study period from those who remained premanifest (area under curve = 0.81, P = 0.024). These results demonstrate that the key sleep abnormalities of premanifest/early Huntington's disease are sleep stage instability and sleep maintenance insomnia and suggest that the former bears value in predicting disease onset, while the latter is associated with greater disease activity and cognitive deficits. Intervention studies to interrogate causation within this association could not only benefit patients with Huntington's disease but also help provide fundamental proof-of-concept findings for the wider sleep-neurodegeneration field.

Cognitive reserve linked to network-specific brain-ventricle coupling

Despite showing significant impact in cognitive preservation, the relationship between brain activity captured with functional Magnetic Resonance Imaging (fMRI) in gray matter and ventricular cerebrospinal fluid dynamics remains poorly understood. We analyzed 599 fMRI scans from 163 elderly participants at rest with varying degrees of cognitive impairment employing a unified phase coupling analysis that breaks from convention by incorporating both tissue and ventricular signal fluctuations. This whole-brain approach identified distinct brain-ventricle coupling modes that differentiate between cognitive status groups and correlate with specific cognitive abilities. Beyond the previously reported anti-phase coupling between global brain signals and ventricles-which we confirm occurs more frequently in cognitively normal controls-our analysis method uncovered additional coupling modes where signals in specific brain networks temporarily align with ventricle signals. At the cortical level, these modes reveal patterns corresponding to known resting-state networks: one overlapping with the Default Mode Network occurs significantly less frequently in Alzheimer's Disease patients, while another revealing the Frontoparietal Network correlates positively with memory scores. Our findings demonstrate that different brain-ventricle coupling modes correlate with specific cognitive domains, with particular modes predicting memory, executive function, and visuospatial abilities. The coupling between signals in brain ventricles and established resting-state networks challenges our current understanding of functional network formation, suggesting an integral link with brain fluid motion. This reconceptualization of brain dynamics through the lens of fluid-tissue interactions establishes a fundamental physical basis for cognitive preservation, suggesting that therapeutic interventions targeting these interactions may prove more effective than approaches focused solely on cellular or molecular mechanisms.

Test-retest reliability of coupling between cerebrospinal fluid flow and global brain activity after normal sleep and sleep deprivation

The glymphatic system (GS) plays a key role in maintaining brain homeostasis by clearing metabolic waste during sleep, with the coupling between global blood-oxygen-level-dependent (gBOLD) and cerebrospinal fluid (CSF) signals serving as a potential marker for glymphatic clearance function. However, the test-retest reliability and spatial heterogeneity of gBOLD-CSF coupling after different sleep conditions remain unclear. In this study, we assessed the test-retest reliability of gBOLD-CSF coupling following either normal sleep or total sleep deprivation (TSD) in 64 healthy adults under controlled laboratory conditions. The reliability was high after normal sleep (ICC = 0.763) but decreased following TSD (ICC = 0.581). Moreover, spatial heterogeneity was evident in participants with normal sleep, with lower-order networks (visual, somatomotor, and attention) showing higher ICC values compared to higher-order networks (default-mode, limbic, and frontoparietal). This spatial variation was less distinct in the TSD group. These results demonstrate the robustness of the gBOLD-CSF coupling method and emphasize the significance of considering sleep history in glymphatic function research.

The Space-Time Organisation of Sleep Slow Oscillations as Potential Biomarker for Hypersomnolence

Research suggests that the spatial profile of slow wave activity (SWA) could be altered in hypersomnolence. Slow oscillations (SOs; 0.5-1.5 Hz), single waveform events contributing to SWA, can be labelled as Global, Frontal, or Local depending on their presentation on the scalp. We showed that SO space-time types differentiate in their amplitudes, coordination with sleep spindles, and propagation patterns. This study applies our data-driven analysis to the nocturnal sleep of adults with and without hypersomnolence and major depressive disorder (MDD) to explore the potential relevance of SO space-time patterns as hypersomnolence signatures in the sleep EEG. We leverage an existing dataset of nocturnal polysomnography with high-density EEG in 83 adults, organised in four groups depending on the presence/absence of hypersomnolence and on the presence/absence of MDD. Group comparisons were conducted considering either two groups (hypersomnolence status) or the four groups separately. Data shows enhanced Frontal SO activity compared with Global activity in hypersomnolence, with or without MDD, and a loss of Global SO amplitude at central regions in hypersomnolence without MDD compared to controls. As Global SOs travel fronto-parietally, we interpret these results as likely driven by a loss of coordination of Global SO activity in hypersomnolence without MDD, resulting in an overabundance of Frontal SOs. This study suggests that characteristics of Frontal SO and Global SOs may have the potential to differentiate individuals with hypersomnolence without MDD, and that the space-time organisation of SOs could be a mechanistically relevant indicator of changes in sleep brain dynamics related to hypersomnolence.

Mechanistic insights into the interaction between epilepsy and sleep

Epidemiological evidence has demonstrated associations between sleep and epilepsy, but we lack a mechanistic understanding of these associations. If sleep affects the pathophysiology of epilepsy and the risk of seizures, as suggested by correlative evidence, then understanding these effects could provide crucial insight into the basic mechanisms that underlie the development of epilepsy and the generation of seizures. In this Review, we provide in-depth discussion of the associations between epilepsy and sleep at the cellular, network and system levels and consider the mechanistic underpinnings of these associations. We also discuss the clinical relevance of these associations, highlighting how they could contribute to improvements in the management of epilepsy. A better understanding of the mechanisms that govern the interactions between epilepsy and sleep could guide further research and the development of novel approaches to the management of epilepsy.

Perivascular brain clearance as a therapeutic target in cerebral amyloid angiopathy and Alzheimer's disease

Although distinct diseases, both cerebral amyloid angiopathy (CAA) and Alzheimer's disease (AD) are characterized by the aggregation and accumulation of amyloid-β (Aβ). This is thought to be due, in part, to impaired perivascular Aβ clearance from the brain. This shared failure in both diseases presents a common opportunity for therapeutic intervention. In this review we discuss the idea that promoting perivascular brain clearance could be an effective strategy for safely reducing Aβ levels in CAA and AD thereby improving clinical outcomes, most notably hemorrhagic stroke and cognitive decline. We will explore the evidence for the different forces that are thought to drive perivascular brain clearance, review the literature on potential strategies for potentiating these driving forces, and finally we will discuss the substantial translational challenges and considerations that would accompany such an intervention.

Total cerebral blood volume changes drive macroscopic cerebrospinal fluid flux in humans

In the mammalian brain, the directed motion of cerebrospinal fluid (CSF-flux) is instrumental in the distribution and removal of solutes. Changes in total cerebral blood volume (CBV) have been hypothesized to drive CSF-flux. We tested this hypothesis in two multimodal brain imaging experiments in healthy humans, in which we drove large changes in total CBV by neuronal burst-suppression under anesthesia or by transient global vasodilation in a hypercapnic challenge. We indirectly monitored CBV changes with a high temporal resolution based on associated changes in total brain volume by functional MRI (fMRI) and measured cerebral blood flow by arterial spin-labeling. Relating CBV-sensitive signals to fMRI-derived measures of macroscopic CSF flow across the basal cisternae, we demonstrate that increasing total CBV extrudes CSF from the skull and decreasing CBV allows its influx. Moreover, CSF largely stagnates when CBV is stable. Together, our results establish the direct coupling between total CBV changes and CSF-flux.

Age as a limiting factor for effectiveness of photostimulation of brain drainage and cognitive functions

The progressive number of old adults with cognitive impairment worldwide and the lack of effective pharmacologic therapies require the development of non-pharmacologic strategies. The photobiomodulation (PBM) is a promising method in prevention of early or mild age-related cognitive impairments. However, it remains unclear the efficacy of PBM for old patients with significant age-related cognitive dysfunction. In our study on male mice, we show a gradual increase in the brain amyloid beta (Aβ) levels and a decrease in brain drainage with age, which, however, is associated with a decline in cognitive function only in old (24 months of age) mice but not in middle-aged (12 months of age) and young (3 month of age) animals. These age-related features are accompanied by the development of hyperplasia of the meningeal lymphatic vessels (MLVs) in old mice underlying the decrease in brain drainage. PBM improves cognitive training exercises and Aβ clearance only in young and middle-aged mice, while old animals are not sensitive to PBM. These results clearly demonstrate that the PBM effects on cognitive function are correlated with age-mediated changes in the MLV network and may be effective if the MLV function is preserved. These findings expand fundamental knowledge about age differences in the effectiveness of PBM for improvement of cognitive functions and Aβ clearance as well as about the lymphatic mechanisms responsible for age decline in sensitivity to the therapeutic PBM effects.

The Critical Role of Sleep in Enhancing Pulmonary Rehabilitation Outcomes

Pulmonary rehabilitation is a comprehensive, interdisciplinary intervention that aims to enhance the physical and psychological well-being of individuals with chronic respiratory diseases. This approach entails the implementation of tailored therapies, including exercise training, education, and behavioral modification. Sleep plays a crucial role in numerous physiological processes, including the regulation of inflammation and tissue repair, both of which are fundamental to the efficacy of rehabilitation. A paucity of optimal sleep health has been associated with deleterious effects on pivotal factors that are indispensable for favorable outcomes in pulmonary rehabilitation, including mental and physical health and immune function. This, in turn, may increase susceptibility to impaired pulmonary function. The integration of pulmonary rehabilitation protocols with healthy sleep practices is expected to yield significant improvements in lung function and overall health, which will, in turn, promote long-term adherence to rehabilitative behaviors. This study aims to examine the relationship between sleep health and pulmonary rehabilitation outcomes.

Quantifying brain-wide cerebrospinal fluid flow dynamics using slow-flow-sensitized phase-contrast MRI

Cerebrospinal fluid (CSF) flow is a key component of the brain's waste clearance system. However, our understanding of CSF flow in the human brain, particularly within the brain-wide subarachnoid space (SAS), is limited due to a lack of non-invasive tools for measuring slow flow. Here, we propose a CSF flowmetry technique using phase-contrast MRI combined with a slow-flow-sensitized acquisition. It achieves high sensitivity in measuring slow CSF flow (e.g., 100 μm/s), and enables quantitative measurement of the velocity and direction with whole-brain coverage, spanning from ventricles to SAS. Our proof-of-concept results demonstrate repeatable flow measurements and show that cardiac pulsation induces coherent CSF flow changes within the SAS. Our data also suggest that cardiac pulsation has a stronger driving effect on brain-wide CSF flow compared to respiration. This technique provides a valuable tool for investigating CSF dynamics and pathways to advance a holistic understanding of brain-wide CSF flow.

Dual orexin receptor antagonists as promising therapeutics for Alzheimer's disease

We examine the relationship between sleep, glymphatics and Alzheimer's disease (AD), and recent work questioning glymphatic clearance during sleep. We highlight a need for understanding glymphatic and/or other mechanism of clearance during sleep, and review glymphatic flow measurement methods. Further, we explore dual orexin receptor antagonists (DORAs) potential to mitigate AD sleep disturbances and enhance clearance. Further research could elucidate a linkage between DORAs, improved sleep and reducing AD pathophysiology.

Explainable multiscale temporal convolutional neural network model for sleep stage detection based on electroencephalogram activities

Objective.Humans spend a significant portion of their lives in sleep (an essential driver of body metabolism). Moreover, as sleep deprivation could cause various health complications, it is crucial to develop an automatic sleep stage detection model to facilitate the tedious manual labeling process. Notably, recently proposed sleep staging algorithms lack model explainability and still require performance improvement.Approach.We implemented multiscale neurophysiology-mimicking kernels to capture sleep-related electroencephalogram (EEG) activities at varying frequencies and temporal lengths; the implemented model was named 'multiscale temporal convolutional neural network (MTCNN).' Further, we evaluated its performance using an open-source dataset (Sleep-EDF Database Expanded comprising 153 d of polysomnogram data).Main results.By investigating the learned kernel weights, we observed that MTCNN detected the EEG activities specific to each sleep stage, such as the frequencies, K-complexes, and sawtooth waves. Furthermore, regarding the characterization of these neurophysiologically significant features, MTCNN demonstrated an overall accuracy (OAcc) of 91.12% and a Cohen kappa coefficient of 0.86 in the cross-subject paradigm. Notably, it demonstrated an OAcc of 88.24% and a Cohen kappa coefficient of 0.80 in the leave-few-days-out analysis. Our MTCNN model also outperformed the existing deep learning models in sleep stage classification even when it was trained with only 16% of the total EEG data, achieving an OAcc of 85.62% and a Cohen kappa coefficient of 0.75 on the remaining 84% of testing data.Significance.The proposed MTCNN enables model explainability and it can be trained with lesser amount of data, which is beneficial to its application in the real-world because large amounts of training data are not often and readily available.

Loss of glymphatic homeostasis in heart failure

Heart failure is associated with progressive reduction in cerebral blood flow and neurodegenerative changes leading to cognitive decline. The glymphatic system is crucial for the brain's waste removal, and its dysfunction is linked to neurodegeneration. In this study, we used a mouse model of heart failure, induced by myocardial infarction, to investigate the effects of heart failure with reduced ejection fraction on the brain's glymphatic function. Using dynamic contrast-enhanced MRI and high-resolution fluorescence microscopy, we found increased solute influx from the CSF spaces to the brain, i.e. glymphatic influx, at 12 weeks post-myocardial infarction. Two-photon microscopy revealed that cerebral arterial pulsatility, a major driver of the glymphatic system, was potentiated at this time point, and could explain this increase in glymphatic influx. However, clearance of proteins from the brain parenchyma did not increase proportionately with influx, while a relative increase in brain parenchyma volume was found at 12 weeks post-myocardial infarction, suggesting dysregulation of brain fluid dynamics. Additionally, our results showed a correlation between brain clearance and cerebral blood flow. These findings highlight the role of cerebral blood flow as a key regulator of the glymphatic system, suggesting its involvement in the development of brain disorders associated with reduced cerebral blood flow. This study paves the way for future investigations into the effects of cardiovascular diseases on the brain's clearance mechanisms, which may provide novel insights into the prevention and treatment of cognitive decline.

One-Dimensional Blood Flow Modeling in the Cardiovascular System. From the Conventional Physiological Setting to Real-Life Hemodynamics

Research in the dynamics of blood flow is essential to the understanding of one of the major driving forces of human physiology. The hemodynamic conditions experienced within the cardiovascular system generate a highly variable mechanical environment that propels its function. Modeling this system is a challenging problem that must be addressed at the systemic scale to gain insight into the interplay between the different time and spatial scales of cardiovascular physiology processes. The vast majority of scientific contributions on systemic-scale distributed parameter-based blood flow modeling have approached the topic under relatively simple scenarios, defined by the resting state, the supine position, and, in some cases, by disease. However, the physiological states experienced by the cardiovascular system considerably deviate from such conditions throughout a significant part of our life. Moreover, these deviations are, in many cases, extremely beneficial for sustaining a healthy life. On top of this, inter-individual variability carries intrinsic complexities, requiring the modeling of patient-specific physiology. The impact of modeling hypotheses such as the effect of respiration, control mechanisms, and gravity, the consideration of other-than-resting physiological conditions, such as those encountered in exercise and sleeping, and the incorporation of organ-specific physiology and disease have been cursorily addressed in the specialized literature. In turn, patient-specific characterization of cardiovascular system models is in its early stages. As for models and methods, these conditions pose challenges regarding modeling the underlying phenomena and developing methodological tools to solve the associated equations. In fact, under certain conditions, the mathematical formulation becomes more intricate, model parameters suffer greater variability, and the overall uncertainty about the system's working point increases. This paper reviews current advances and opportunities to model and simulate blood flow in the cardiovascular system at the systemic scale in both the conventional resting setting and in situations experienced in everyday life.