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Elabasy, A.

Publications and source records attributed to Elabasy, A..

2 recordsLinked to original sources
bioRxiv2025

Infra-slow (<0.1 Hz) modulation of human brain pulsations in awake and sleep states

Human brain exhibits three propagating pulsations, namely cardiovascular, respiratory, and vasomotor waves, which together propel the flow of intracranial fluids. While their pulsation characteristics have been extensively studied, their causal interconnections have not been systematically investigated. Using ultrafast whole brain magnetic resonance encephalography (MREG), we analysed the frequency domain up to 5 Hz for cross-frequency oscillatory interactions in awake and NREM-sleep states of 23 healthy volunteers. Using transfer entropy (TE) analysis, we found that in the awake state the infra-slow (ISF < 0.1 Hz) oscillations of statistically independent resting state networks (RSN) largely drove the neurofluid (NF) pulsatility. NREM-sleep was associated with increased power of infra-slow fluctuation (ISF) vasomotor oscillations and with altered driving patterns between RSN and NF networks in the direction of a causally chained pattern. Importantly, within these independent signal sources, we found three distinct cross-frequency coupling frequency ranges occurring at ISF (<0.1 Hz), respiratory ([~]0.25 Hz), and cardiovascular ([~]1 Hz) frequencies, where the slower pulsations generally modulated the faster ones, except for a finding of inverted cardiorespiratory drive in NREM-2 sleep. These results indicate the presence of directional ISF-coordinated mechanisms underlying brain pulsations that contribute to driving the intracranial fluid transfer processes. Significance statementCerebrospinal fluid (CSF) flow is essential for brain fluid homeostasis and interstitial metabolite clearance. Human brain exhibits three types of intracranial pulsations linked to CSF flow, which are particularly distinct during sleep, when fluid clearance processes are most active. We predicted that these pulsations, despite their independent sources, interact with each other to coordinate CSF flow. Using functional magnetic resonance imaging (fMRI) during wakefulness and non-rapid eye movement sleep (NREM), we investigated cross-frequency coupling patterns up to 5 Hz within the brain. Results revealed a novel mechanism in human brain whereby infra-slow (ISF) vasomotor oscillations coordinated faster brain pulsation dynamics, which could be a factor mediating the increased perivascular clearance during sleep.

neuroscience↗
bioRxiv2025

Sleep increases propagation speed of physiological brain pulsations

During sleep, there is an increase in the brain cerebrospinal fluid (CSF) solute convection driven by physiological pulsations. Although the main drivers of CSF flow, namely cardiac, respiratory, and vasomotor pulsations, become more powerful during sleep, there is relatively little information regarding their effects on CSF flow velocity across human brain during sleep. Here, we used functional magnetic resonance encephalography (MREG) to measure non-invasively changes in brain water flow during to sleep by tracking the propagating ultrafast signal changes induced by physiological brain pulsations. We first undertook a phantom study confirming that dense optical flow analysis of MREG data accurately detects water flow velocity, and reflects the power of the physiological pulsations. We then applied the method to quantify CSF water flow velocity in brain of healthy volunteers during EEG-verified awake and sleep recordings of ultrafast MREG data. Sleep induced an increase in CSF flow speed, as demonstrated by elevated vasomotor and respiratory pulsation speeds, while the speed of cardiovascular impulse propagation remained unchanged. The speed increases match previous findings of respective pulsation power changes, and correlated with slow delta EEG power. The sleep-induced CSF flow speed increases occurred dynamically over both pulsation cycles, without the large effects on flow directions reported previously in several neurological conditions. In conclusion, sleep increases 3D water flow speed dynamically in human brain regions showing concomitant pulse power increases, supporting a porous media model of hydrodynamics in brain cortex.

neuroscience↗