Biology subjects

Welker, K. M.

Publications and source records attributed to Welker, K. M..

3 recordsLinked to original sources

bioRxiv2026

Network- and Measure-Specific Mid-Term Reliability of Multi-Echo Resting-State Functional Magnetic Resonance Imaging on a Compact 3 Tesla Scanner

1.IntroductionUnderstanding mid-term test-retest reliability and within-subject variability is important for interpreting changes observed in longitudinal and intervention studies. The reliability of resting-state functional magnetic resonance imaging (rs-fMRI) is known to vary across measures and brain regions. However, how reliability differs across functional networks and connectivity-and amplitude-based measures, and whether multi-echo acquisition and processing modify these patterns, remain incompletely characterized. MethodsTwenty-two healthy volunteers underwent two rs-fMRI sessions 15.7 {+/-} 4.0 days apart on a Compact 3T scanner. Multi-echo, middle-echo, and independently acquired single-echo datasets were compared, with multi-echo independent component analysis additionally evaluated as a denoising approach. Functional connectivity (FC) and three amplitude-based measures were evaluated using the Schaefer 400 parcellation. Reliability was systematically assessed using intraclass correlation coefficient (ICC), within-subject standard deviation (wSD), and systematic bias at edge or regional, and network levels. ResultsAcquisition-dependent differences in reliability were generally modest. Multi-echo acquisition and processing increased functional connectivity strength and the magnitude of amplitude-based measures and improved inferior cortical coverage, but these enhancements did not consistently translate into substantially higher ICC or lower wSD. In contrast, reliability showed clear network-dependent differences. FC reliability varied markedly across network pairs and was not explained by connectivity strength alone; pairs involving the default mode and control networks generally showed more favorable profiles than several somatomotor and visual network pairs. Fractional amplitude of low-frequency fluctuations (fALFF) also showed network-dependent reliability, with the most favorable regional reproducibility observed in the default mode and control networks and lower reproducibility in the somatomotor and visual networks. ConclusionThese findings provide practical mid-term reliability benchmarks for rs-fMRI on a Compact 3T scanner and show that measurement stability varies more clearly across measures and functional networks than across acquisition approaches. Key pointsO_LIMid-term test-retest reliability varied more clearly across resting-state measures and functional networks than across acquisition and processing approaches. C_LIO_LIMulti-echo acquisition and processing enhanced functional connectivity strength, amplitude-based signal magnitude, and inferior cortical coverage but did not consistently improve reliability. C_LIO_LIFunctional connectivity strength and fractional amplitude of low-frequency fluctuations showed distinct network-specific reliability profiles, with more favorable reproducibility in default mode and control networks than in several somatomotor and visual networks. C_LI

neuroscience↗

bioRxiv2026

Cerebral Oxygen Budgeting: Network-Level BOLD Dynamics During Acute Hypoxia

Hypoxia constrains cerebral oxygen availability and challenges brain function. Previous work showed that functional connectivity reorganizes early during acute hypoxia, preceding cognitive deterioration, but the functional changes accompanying more severe hypoxic stress remain incompletely understood. We examined dynamic amplitude of low-frequency fluctuations (dALFF) in blood-oxygenation-level dependent (BOLD) fMRI during normoxia, sustained mild hypoxia, and transient severe hypoxia in healthy adults performing a continuous Go/No-go task with concurrent physiological monitoring. We characterized dALFF at whole-brain and network levels using a causal sliding-window approach, principal component analysis, and Schaefer's 17-network parcellation. Severe hypoxia elicited a non-monotonic, phase-dependent dALFF response that was not observed during normoxia or sustained mild hypoxia. Relative preservation during early hypoxia was followed by late-hypoxia suppression, which we operationally defined as a decompensation phase, and by a pronounced rebound after reoxygenation. Within this global response, dALFF became increasingly differentiated across intrinsic brain networks: DefaultA showed marked suppression, whereas SomMotB exhibited relative preservation or enhancement during decompensation. These changes were neither spatially uniform nor tightly synchronized with systemic oxygenation, while broadly overlapping temporally with cognitive deterioration. Together, these findings indicate that dALFF captures a complementary aspect of the brain's response to acute hypoxic stress, characterized by reversible, phase- and network-dependent reorganization of ongoing low-frequency BOLD dynamics under constrained oxygen availability.

neuroscience↗

bioRxiv2025

Brain functional connectivity initiates structured reorganization at a critical oxygen threshold during hypoxia

The human brain dynamically adapts to hypoxia, a reduction in oxygen essential for metabolism. The brains adaptive response to hypoxia, however, remains unclear. We investigated dynamic functional connectivity (FC) in healthy adults under acute hypoxia (FiO2 = 7.7%, 11.8%) using BOLD fMRI, physiological monitoring (PetO2, PetCO2, SpO2), and a Go/No-Go task. Principal component analysis identified a hypoxia-responsive FC component involving 400 cerebral parcels. This component emerged with a critical drop in PetO2 ([~]53 mmHg), preceding changes in SpO2, BOLD signals, and behavior. These FC changes were network-specific and centered on the default mode network (DMN), which selectively synchronized with other high-level cognitive networks. In contrast, visual networks remained stable and segregated from the DMN. These results suggest that the brain proactively reorganizes its functional architecture in anticipation of oxygen decline, rather than in response to it. FC-based markers may offer early indicators of vulnerability in neurological or neurodegenerative conditions.

neuroscience↗