Biology subjects

Väyrynen, T.

Publications and source records attributed to Väyrynen, T..

3 recordsLinked to original sources

bioRxiv2025

Reduced harmonic complexity of brain parenchymal cardiovascular pulse waveforms in Alzheimer's disease

Alzheimers disease (AD) is characterized by specific neuropathologies, and is associated with arterial wall {beta}-amyloid accumulations, which lead to radiologically detectable amplitude increases and variable propagation speed of cardiovascular impulses in brain. In this study, we developed a fast frequency domain imaging method know as relative harmonic power of magnetic resonance encephalography (MREGRHP), aiming to investigate the configuration of the cardiovascular impulses independently of the mean magnetic resonance signal intensity and physiological impulse amplitude. In the initial analyses in healthy controls, we found that a wide 0.8 - 5Hz bandpass produced the most physiologically realistic cardiovascular waveforms. Whereas the data recorded in cerebrospinal fluid (CSF) from flip angle (FA) of 25{degrees} yielded up to 7-fold higher cardiac signal intensity as compared to FA of 5{degrees}, within the brain tissue recordings with FA of 5{degrees} were markedly more sensitive to cardiac waveform. We detected arterial impulses originating from major arteries and extending into the surrounding brain parenchyma, with simultaneous dampening of amplitude as a function of distance from source. Finally, we compared MREGRHP results in 34 AD patients (mean age: 60.7{+/-}4.7 years; 53% female) against 29 controls (mean age: 56.9{+/-}7.9 years; 66% female). We show that the harmonic power of cardiovascular brain pulses is significantly reduced in cortical frontoparietal areas of AD patients, indicating monotonous impulse patterns colocalizing with the previously reported areas of increased impulse propagation speed. In conclusion, the MREGRHP offers a fast Fourier transform (FFT)-based method to non-invasively quantify and locate human arterial blood vessel wall pathology.

neuroscience↗

bioRxiv2024

Sleep-Induced Vasomotor Pulsation is a Driver of Cerebrospinal Fluid and Blood-Brain Barrier Dynamics in the Human Brain

Sleep is essential for maintaining brain tissue homeostasis, which is facilitated by enhanced cerebrospinal fluid (CSF) solute transport. Infra-slow (<0.1 Hz) vasomotion, CSF flow, and electrophysiological potential all increase during sleep, but their contributions as potential drivers of CSF flow in human brain remain unknown. To investigate this, we recorded the three signals in healthy volunteers across sleep-wake states using 10 Hz functional magnetic resonance imaging (fMRI BOLD), electroencephalography (DC-EEG), and functional near-infrared spectroscopy (fNIRS). We then analyzed the directed coupling patterns using phase transfer entropy (TE). In the awake state, electrophysiological potential and water concentration changes both predicted vasomotor waves across the brain, possibly reflecting functional hyperemia. During sleep, this coupling reversed, with vasomotor waves instead predicting electrical changes and CSF flow in cortical areas. Furthermore, we found that the amplitude of these dynamics increased during sleep, highlighting the critical role of physiological oscillations in sleep-associated brain fluid flow.

neuroscience↗

bioRxiv2023

Sleep specific changes in infra-slow and respiratory frequency drivers of cortical EEG rhythms

Infra-slow fluctuations (ISFs, 0.008-0.1 Hz) characterize hemodynamic and electric potential signals from the human brain. ISFs are known to correlate with the amplitude dynamics of fast (> 1 Hz) neuronal oscillations, and may arise from permeability fluctuations of the blood-brain barrier (BBB). Slow physiological pulsations such as respiration may also influence the amplitude dynamics of fast oscillations, but it remains uncertain if these processes track the fluctuations of fast cortical oscillations or act as their drivers. Moreover, possible effects of sleep and associated BBB permeability changes on such coupling are unknown. Here, we used non-invasive high-density full-band electroencephalography (EEG) in healthy human volunteers (N=21) to measure concurrently the ISFs, respiratory pulsations, and fast neuronal oscillations during periods of wakefulness and sleep, and to assess the strength and direction of their phase-amplitude coupling. The phases of ISFs and respiration were both coupled with the amplitude of fast neuronal oscillations, with stronger ISF coupling evident during sleep. Causality analysis robustly showed that the phase of ISF and respiration drove the amplitude dynamics of fast oscillations in sleeping and waking states. However, the net direction of modulation was stronger during the awake state, despite the stronger power and phase-amplitude coupling of slow signals during sleep. These findings show that the ISFs in slow cortical potentials and respiration together significantly determine the dynamics of fast cortical oscillations. We propose that these slow physiological phases are involved in coordinating cortical excitability, which is a fundamental aspect of brain function. Significance StatementPreviously disregarded EEG infra-slow fluctuations (0.008-0.1 Hz) and slow physiological pulsations such as respiration have been attracting increasing research interest, which shows that both of these signals correlate with fast (> 1 Hz) neuronal oscillations. However, little has been known about the mechanisms underlying these interactions; for example, the direction of causality in this interaction has not hitherto been studied. Therefore, we investigated full-band EEG in healthy volunteers during wakefulness and sleep to determine if ISF and respiration phases drive neuronal amplitudes. Results showed that ISF and respiration are phase-amplitude coupled, and predict neuronal EEG rhythms. Thus, we conclude that fast neuronal rhythms in human brain are modulated by slower non-neural phenomena.

neuroscience↗