Eşzamanlı fMRI, EEG ve fizyoloji ölçümlerinin entegrasyonu ile uyanıklık durumunun belirlenmesi ve doğrulanması

Resting-state fMRI (rsfMRI) is a powerful tool for investigating the brain's functional organization in the absence of specific tasks. Approaches such as functional connectivity (FC) and global signal variance are commonly used to study cognitive functions and disease states. These measures, which reflect correlations in blood oxy- genation level-dependent (BOLD) signals across brain regions, are particularly appeal- ing in clinical and research settings due to their ability to capture brain activity without requiring active participant engagement. However, a major challenge in rsfMRI lies in its sensitivity to fluctuations in vigilance-the state of wakefulness and attention. Vigilance-driven variations can alter BOLD signal amplitudes and correlations between brain regions. These effects, often influenced by systemic physiological signals, may be mistakenly interpreted as purely neural in origin if not properly accounted for. This study aimed to demonstrate how vigilance states modulate rsfMRI metrics and physiological signals in a healthy young population. Using an EEG-based vigilance index, we delineated the effects of vigilance on BOLD signals and their links to physi- ological dynamics. Systemic markers, including cardiac and respiratory signals such as heart rate and respiratory volume, as well as the photoplethysmogram (PPG) signal amplitude-an indicator of vascular tone-were analyzed to understand their contribution to these dynamics. Our work advances the field through several key innovations: developing clas- sification methodologies, integrating cerebrospinal fluid (CSF) flow oscillations from the fourth ventricle as a systemic signal of interest, utilizing physiological biomarkers often overlooked in rsfMRI studies, and leveraging time-lagged correlation matrices tovii uncover spatio-temporal brain dynamics. Data from 17 participants across multiple short eyes-open resting-state scans were analyzed. Our findings reveal significant correlations between fMRI signals and physiolog- ical markers during transitions from wakefulness to drowsiness. Notably, we observed co-variations between CSF oscillations and respiratory volume, correlations between sensory regions and heart rate, and associations between the default mode network (DMN) and photoplethysmography amplitude (PPG-AMP). Additionally, we demon- strated reduced connectivity during drowsy states compared to wakefulness, even in short-duration scans, underscoring the influence of vigilance transitions on rsfMRI out- comes. These findings highlight the interplay between systemic physiology and neural activity across vigilance states. By addressing these vigilance-driven variations, our approach enhances the interpretative accuracy of rsfMRI and broadens its potential applications in both research and clinical domains.