Abstract
Although it has been consistently found that local blood-oxygen-level-dependent (BOLD) changes are better modelled by a combination of the power of multiple EEG frequency bands rather than by the power of a unique band alone, the local electro-haemodynamic coupling function is not yet fully characterised. Electrophysiological studies have revealed that the strength of the coupling between the phase of low- and the amplitude of high- frequency EEG activities (phase–amplitude coupling - PAC) has an important role in brain function in general, and in preparation and execution of movement in particular. Using electrocorticographic (ECoG) and functional magnetic resonance imaging (fMRI) data recorded simultaneously in humans performing a finger-tapping task, we investigated the single-trial relationship between the amplitude of the BOLD signal and the strength of PAC and the power of α, β, and γ bands, at a local level. In line with previous studies, we found a positive correlation for the γ band, and negative correlations for the PACβγ strength, and the α and β bands. More importantly, we found that the PACβγ strength explained variance of the amplitude of the BOLD signal that was not explained by a combination of the α, β, and γ band powers. Our main finding sheds further light on the distinct nature of PAC as a functionally relevant mechanism and suggests that the sensitivity of EEG-informed fMRI studies may increase by including the PAC strength in the BOLD signal model, in addition to the power of the low- and high- frequency EEG bands.
Highlights
IntroductionHuman brain activity has been recorded most commonly as electrical potentials on the scalp (scalp electroencephalography - EEG), neocortex (electrocorticography ECoG), or inside the brain (depth EEG)
In the last century, human brain activity has been recorded most commonly as electrical potentials on the scalp, neocortex, or inside the brain
This is the first study focused on the relationship between the EEG and BOLD signals using invasive EEG and functional magnetic resonance imaging (fMRI) data simultaneously acquired in humans; previous studies have used either local field potentials (LFP) and fMRI data simultaneously recorded in animals, or ECoG and fMRI data sequentially recorded in humans
Summary
Human brain activity has been recorded most commonly as electrical potentials on the scalp (scalp electroencephalography - EEG), neocortex (electrocorticography ECoG), or inside the brain (depth EEG). Since the discovery of EEG, a range of rhythmic activities characteristically associated with sensory, motor, and cognitive events, has been observed on its recordings (Engel et al, 2001; Varela et al, 2001; Jacobs and Kahana, 2010) These activities appear to hierarchically interact with each other, as the “basic units” of a complex system that regulates information processing in the brain, across multiple spatial and temporal scales (Lakatos et al, 2005; Palva et al, 2005; Roopun et al, 2008; Canolty and Knight, 2010; Buzsaki et al, 2012; Hyafil et al, 2015).
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