Excitatory-Inhibitory Balance within EEG Microstates and Resting-state fMRI Networks: Assessed via Simultaneous PET-MR-EEG Imaging

The symbiosis of neuronal activities and glucose energy metabolism is reflected in the generation of functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) signals. However, their association with the balance between neuronal excitation and inhibition (E/I-B), which is closely related to the activities of glutamate and GABA (γ -aminobutyric acid) and the receptor availability (RA) of GABA and mGluR5, remains unexplored. This study investigates these associations during the resting state (RS) condition using simultaneously recorded PET/MR/EEG (trimodal) data. Glucose metabolism and neuroreceptor binding availability (non-displaceable binding potential (BP)) of GABA and mGluR5 were found to be significantly higher and closely linked within core resting-state networks (RSNs). The neuronal generators of EEG microstates and the fMRI measures were most tightly associated with the BP of GABA relative to mGluR5 BP and the glucose metabolism, emphasising a predominance of inhibitory processes within in the core RSNs at rest.