# EEG Time-Frequency Clustering Reveals Spectral Signatures of Glutamatergic and Cholinergic Activities and Their Interrelations

## TL;DR

This study identifies EEG patterns linked to glutamate and acetylcholine brain systems and their interactions in rats.

## Contribution

The study introduces EEG time-frequency clustering to detect and analyze glutamatergic and cholinergic biomarkers and their interactions.

## Key findings

- Glutamate receptor agonists produced distinct EEG clusters at 2/4 Hz and 10 Hz.
- Cholinergic agonist physostigmine altered EEG activity at multiple frequencies.
- Interactions between glutamatergic and cholinergic systems were revealed through receptor blocker effects.

## Abstract

Background: The discovery of electroencephalogram (EEG) biomarkers of direct transmitter–receptor interactions in studies of neurotransmitter mechanisms underlying brain function remains relevant. Recently, EEG “signatures” of monoaminergic systems have been demonstrated using the “time-frequency clustering” approach. In the current study, the glutamic and cholinergic systems were under similar analysis with additional emphasis on their potential interaction. Methods: In non-anesthetized freely moving rats, we studied the EEG effects of agonists for glutamate receptors, injected into the cerebral lateral ventricles, and their modification after pretreatment with corresponding antagonists. The same protocol was used for acetylcholine receptors, activating and blocking substances that penetrate the blood–brain barrier (BBB) after subcutaneous injections. A clustering of significant time-dependent changes in tiny frequency subranges of the EEG spectra was performed. Results: After injections of agonists for glutamate receptors, two clusters with enhanced and suppressed activities around 2/4 and 10 Hz, respectively, were observed in the EEG spectra. These effects were reduced by pretreatment with corresponding receptor blockers. A cholinomimetic, physostigmine, decreased EEG activity around 2 and 10 Hz and increased near 5 and 22 Hz. Scopolamine, blocking muscarinic cholinoreceptors, weakened the effects of physostigmine. Intracerebral pretreatment with NMDA and AMPA receptor blockers differently modified the effects of physostigmine. The results demonstrate the EEG biomarkers of glutamatergic and cholinergic systems, as well as the specificity of interactions between them at the intracerebral level. Conclusions: The developed EEG time-frequency clustering is a potentially useful approach for the clinical evaluation of glutamatergic/cholinergic pathology and its correction by corresponding substances penetrating the BBB.