# Functional Brain Activity Associated With Intermittent Rhythmic Delta/Theta Activity: A Transdiagnostic Electroencephalography–Functional Magnetic Resonance Imaging Resting-State Study

## TL;DR

This study identifies brain regions linked to abnormal brain wave patterns in neuropsychiatric disorders using EEG and fMRI.

## Contribution

The study reveals transdiagnostic and disorder-specific brain activity changes associated with IRDA/IRTA in autoimmune and psychiatric conditions.

## Key findings

- Eleven brain regions showed consistent activity changes across all groups, with five increased and six reduced.
- APS patients had five additional brain regions with reduced activity.
- BPD patients showed one extra region with increased activity.

## Abstract

Intermittent rhythmic delta/theta activity (IRDA/IRTA) detected via electroencephalography (EEG) has been implicated in the pathophysiology of neuropsychiatric illnesses. Therefore, a combined EEG and functional magnetic resonance imaging (fMRI) approach was applied in a transdiagnostic group of patients with different causalities, i.e., autoimmune-mediated (in suspected autoimmune psychiatric syndromes [APS]) and primary psychiatric (borderline personality disorder [BPD]) causalities, as well as in healthy control (HC) participants, to characterize the brain regions functionally correlated with IRDA/IRTA.

Overall, 135 EEG-fMRI datasets met the quality criteria, including 33 patients with suspected APS, 59 cases with BPD, and 43 HC participants. fMRI data were obtained using ultrafast MR encephalography and analyzed using AFNI. IRDA/IRTA events were separated from artifacts using independent component analysis and detected algorithmically. Brain regions (clusters) significantly correlated with IRDA/IRTA were first determined in all participants. Clusters occurring across all groups were classified as consensus areas. The groups were also analyzed individually, adding disease- or disorder-specific clusters not overlapping with the consensus areas.

Eleven consensus areas were identified across the 3 groups: 5 of them showed increased activity (Brodmann area [BA] 43-right [r], BA 2-left [l], BA 4-r, BA 18-r, BA 26/29/30-r), and 6 had reduced activity (BA 39-l, BA 10-l, BA 23-l, BA 19-l, BA 10-r, BA 18-l). The APS group showed 5 additional clusters, all with reduced activity (BAs 39-r, 1/3-r, 8-r, 4-l, 21-r). The BPD group showed one further cluster with increased activity (BA 17-l).

In this study, IRDA/IRTA-related brain activity changes across the groups were identified, with excitatory brain activity especially in fronto-centro-temporal brain areas with similarities to the salience network. Additional disease- or disorder-specific changes were discovered in APS and BPD.

Intermittent rhythmic delta/theta activity (IRDA/IRTA) detected via electroencephalography (EEG) has been implicated in the pathophysiology of neuropsychiatric illnesses for decades but has been scarcely studied systematically. Therefore, a combined EEG and functional magnetic resonance imaging (fMRI) approach was used to analyze the resting state in a transdiagnostic group of patients with suspected autoimmune psychiatric syndromes (APS) (n = 33) and borderline personality disorder (BPD) (n = 59), as well as in healthy control (HC) participants (n = 43). Brain regions functionally correlated with IRDA/IRTA as well as group differences between patients with different causalities (i.e., autoimmune mediated vs. primary psychiatric) and HC participants were analyzed. A large fraction of transdiagnostic IRDA/IRTA-related brain activity changes was identified, i.e., 11 consensus areas across the 3 groups; 5 of them showed increased activity, and 6 areas had reduced activity. The activated consensus areas have similarities with the salience network as an integrating area. Excitatory EEG activity was also identified in the HC group; however, additional disease- or disorder-specific changes were only discovered in patients with APS and BPD.

Intermittent rhythmic delta/theta activity (IRDA/IRTA) detected via electroencephalography (EEG) has been implicated in the pathophysiology of neuropsychiatric illnesses for decades but has been scarcely studied systematically. Therefore, a combined EEG and functional magnetic resonance imaging (fMRI) approach was used to analyze the resting state in a transdiagnostic group of patients with suspected autoimmune psychiatric syndromes (APS) (n = 33) and borderline personality disorder (BPD) (n = 59), as well as in healthy control (HC) participants (n = 43). Brain regions functionally correlated with IRDA/IRTA as well as group differences between patients with different causalities (i.e., autoimmune mediated vs. primary psychiatric) and HC participants were analyzed. A large fraction of transdiagnostic IRDA/IRTA-related brain activity changes was identified, i.e., 11 consensus areas across the 3 groups; 5 of them showed increased activity, and 6 areas had reduced activity. The activated consensus areas have similarities with the salience network as an integrating area. Excitatory EEG activity was also identified in the HC group; however, additional disease- or disorder-specific changes were only discovered in patients with APS and BPD.