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Reliable Acquisition of Electroencephalography Data during Simultaneous Electroencephalography and Functional MRI
Published on: March 19, 2021
Effects of fluctuating physiological rhythms during prolonged EEG-fMRI studies
Louise Tyvaert1, Pierre Levan, Christophe Grova
1EEG Department, Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, Que., Canada H3A 2B4.
Summary
Brain activity patterns, specifically alpha and theta rhythms and sleep spindles, significantly correlate with blood-oxygen-level-dependent (BOLD) signal changes during alertness fluctuations in EEG-fMRI studies.
Area of Science:
- Neuroscience
- Functional Magnetic Resonance Imaging (fMRI)
- Electroencephalography (EEG)
Background:
- Prolonged electroencephalography-functional magnetic resonance imaging (EEG-fMRI) studies often exhibit fluctuations in participant alertness.
- These vigilance state changes can introduce confounding variability into the blood-oxygen-level-dependent (BOLD) signal, complicating data interpretation.
Purpose of the Study:
- To investigate the specific brain regions associated with different phases of vigilance.
- To quantify the contribution of physiological electroencephalography (EEG) rhythms to the BOLD signal during alertness fluctuations.
Main Methods:
- Evaluated BOLD signal changes in 15 epilepsy patients, correlating them with key EEG rhythms (alpha, beta, theta, delta, spindles).
- Utilized a general linear model incorporating all EEG rhythm regressors to enhance analytical specificity.
- Assessed the variance in BOLD signal explained by these physiological EEG rhythms.
Main Results:
- Consistent correlations were observed for sleep spindles, alpha, and theta rhythms.
- Alpha rhythm showed positive BOLD correlation in the thalamus and putamen, and negative correlation in occipital, parietal, and frontal lobes.
- Theta rhythm exhibited negative BOLD correlation in parietal, temporal, and frontal lobes; spindles correlated with positive BOLD in the thalamus and putamen.
- EEG rhythm regressors accounted for at least 5% of BOLD signal variance in a notable portion of gray matter, comparable to typical fMRI study changes.
Conclusions:
- Identified specific cerebral structures involved in the generation of major EEG rhythms.
- Demonstrated that fluctuations in these EEG rhythms, linked to vigilance changes, significantly contribute to BOLD signal variations.
- Advocated for integrating physiological EEG rhythms into EEG-fMRI analyses for studies involving alertness fluctuations to mitigate confounding factors.
