Ayappa, I. | Search bioRxiv

bioRxiv2026

Greater hypoxic burden predicts weaker gray matter-CSF coordination independent of non-hypoxic arousals: Implications for glymphatic activity

Study ObjectivesObstructive sleep apnea (OSA) is a risk factor for neurodegeneration, and glymphatic impairment may be one mechanistic pathway. Anti-phase coordination between brain pulsations and CSF flow, reflecting compensatory CSF displacement during each vascular pulsation cycle, supports glymphatic activity. This study examined whether hypoxic burden and sleep fragmentation, two distinct OSA pathologies, are differentially associated with brain pulsation-CSF flow dynamics. MethodsThis cross-sectional study included 28 individuals with newly identified OSA and 8 without OSA. Participants completed in-lab polysomnography or WatchPAT testing, providing measures of hypoxic burden, quantified as time below 90% oxygen saturation (T90), and non-hypoxic sleep fragmentation, quantified as respiratory effort-related arousals (RERAs). Participants also completed 7T resting-state functional MRI to estimate global BOLD-CSF, defined as anti-phase cross-correlation between blood-oxygen-level-dependent (BOLD) signal and CSF inflow. Associations were examined using correlation and hierarchical regression. Exploratory analyses examined region-specific BOLD-CSF and brain pulsation strength, quantified as BOLD amplitude. ResultsGreater T90 was associated with weaker global BOLD-CSF, independent of RERAs and covariates ({beta}=0.08,p=0.03). Greater T90 was also associated with higher BOLD amplitude across temporal, frontal, and parietal regions, but this elevation in amplitude was not accompanied by stronger region-specific BOLD-CSF coupling ({beta}=0.001,p>0.05). In contrast, among regions where BOLD amplitude was not associated with T90, greater BOLD amplitude predicted stronger region-specific BOLD-CSF ({beta}=-0.004,p<0.001). RERAs were not associated with global BOLD-CSF or BOLD amplitude. ConclusionsIn OSA, hypoxic burden may be the primary feature associated with impaired brain pulsation and CSF dynamics that support glymphatic activity. These alterations may be pronounced in the temporal lobe, where elevated pulsations were uncoupled from compensatory CSF displacement.

neuroscience↗

bioRxiv2017

Multichannel Sleep Spindle Detection Using Sparse Low-Rank Optimization

BackgroundWe propose a multichannel spindle detection method that detects global and local spindle activity across all channels of scalp EEG in a single run\n\nNew MethodUsing a non-linear signal model, which assumes the multichannel EEG to be a sum of a transient component and an oscillatory component, we propose a multichannel transient separation algorithm. Consecutive overlapping blocks of the multichannel oscillatory component are assumed to be low-rank whereas the transient component is assumed to be piecewise constant with a zero baseline. The estimated multichannel oscillatory component is used in conjunction with a bandpass filter and the Teager operator for detecting sleep spindles\n\nResults and comparison with other methodsSeveral examples are shown to illustrate the utility of the proposed method in detecting global and local spindle activity. The proposed method is applied to two publicly available databases and compared with 7 existing single-channel automated detectors. F1 scores for the proposed spindle detection method averaged 0.66 (0.02) and 0.62 (0.06) for the two databases, respectively. For an overnight 6 channel EEG signal, the proposed algorithm takes about 4 minutes to detect sleep spindles simultaneously across all channels with a single setting of corresponding algorithmic parameters\n\nConclusionsThe proposed method aims to mimic and utilize, for better spindle detection, a particular human expert behavior where the decision to mark a spindle event may be subconsciously influenced by the presence of a spindle in EEG channels other than the central channel visible on a digital screen

neuroscience↗