Assessing excitatory–inhibitory balance using simultaneous trimodal PET–MR–EEG imaging
18th January 2021
Ravichandran Rajkumar, Cláudia Régio Brambilla, Tanja Veselinović, Joshua Bierbrier, Christine Wyss, Shukti Ramkiran, Linda Orth, Markus Lang, Elena Rota Kops, Jörg Mauler, Jürgen Scheins, Bernd Neumaier, Johannes Ermert, Hans Herzog, Karl-Josef Langen, Ferdinand Christoph Binkofski, Christoph Lerche, N. Jon Shah and Irene Neuner
The brain’s function is directed by neuronal excitation and inhibition, which is closely related to activity in the brain’s main excitatory and inhibitory neurotransmitters, glutamate and γ-aminobutyric acid (GABA), respectively. The intrinsic balance between excitation and inhibition has been shown to play an important role in several mental processes and disturbances in the functioning of the neurotransmitters involved has been linked to a number of psychiatric diseases.
This research aimed to investigate the activities of glutamate and γ-aminobutyric acid (GABA) and the receptor availability (RA) of GABAA and mGluR5 during the resting state (RS) condition using simultaneously recorded PET/MR/EEG (trimodal) data.
The particular benefit of using simultaneously acquired data is that it enables the measurement of different aspects of the same process, under the same physiological and psychological conditions, shedding valuable light on the relationship between them.
The results show that glucose metabolism and the neuroreceptor binding availability (non-displaceable binding potential (BPND)) of GABAA and mGluR5 were significantly higher and closely linked within core resting-state networks (RSNs). The neuronal generators of EEG microstates and the fMRI measures were found to be most strongly associated with the BPND of GABAA relative to mGluR5 BPND and the glucose metabolism, highlighting the predominance of inhibitory processes within in the core RSNs. Consequently, it can be inferred that changes in the neuroreceptors leading to an altered coupling with glucose metabolism may render the RSNs vulnerable to psychiatric conditions.
It is anticipated that the paradigm employed here will likely help identify the precise neurobiological mechanisms behind these alterations in fMRI functional connectivity and EEG oscillations, potentially benefitting individualised healthcare treatment measures. Future research will be directed towards samples involving healthy individuals as well as patients with mental illness with a view to using the techniques described to gain a better understanding of the neurobiological alterations underlying specific psychiatric diseases.
Original publication