Time-Frequency Characterization of Resting Brain in Bipolar Disorder during Euthymia-A Preliminary Study.

Anna Maria Sobczak,Dominika Dudek,Amira Bryll,Marcin Siwek,Anna Tereszko,Bartosz Bohaterewicz,Magdalena Fafrowicz,Magdalena Marszał-Wiśniewska,Anna Ceglarek,Anna Krupa,Tadeusz Marek,Adrian Andrzej Chrobak

doi:10.3390/brainsci11050599

Abstract

The goal of this paper is to investigate the baseline brain activity in euthymic bipolar disorder (BD) patients by comparing it to healthy controls (HC) with the use of a variety of resting state functional magnetic resonance imaging (rs-fMRI) analyses, such as amplitude of low frequency fluctuations (ALFF), fractional ALFF (f/ALFF), ALFF-based functional connectivity (FC), and r egional homogeneity (ReHo). We hypothesize that above-mentioned techniques will differentiate BD from HC indicating dissimilarities between the groups within different brain structures. Forty-two participants divided into two groups of euthymic BD patients (n = 21) and HC (n = 21) underwent rs-fMRI evaluation. Typical band ALFF, slow-4, slow-5, f/ALFF, as well as ReHo indexes were analyzed. Regions with altered ALFF were chosen as ROI for seed-to-voxel analysis of FC. As opposed to HC, BD patients revealed: increased ALFF in left insula; increased slow-5 in left middle temporal pole; increased f/ALFF in left superior frontal gyrus, left superior temporal gyrus, left middle occipital gyrus, right putamen, and bilateral thalamus. There were no significant differences between BD and HC groups in slow-4 band. Compared to HC, the BD group presented higher ReHo values in the left superior medial frontal gyrus and lower ReHo values in the right supplementary motor area. FC analysis revealed significant hyper-connectivity within the BD group between left insula and bilateral middle frontal gyrus, right superior parietal gyrus, right supramarginal gyrus, left inferior parietal gyrus, left cerebellum, and left supplementary motor area. To our best knowledge, this is the first rs-fMRI study combining ReHo, ALFF, f/ALFF, and subdivided frequency bands (slow-4 and slow-5) in euthymic BD patients. ALFF, f/ALFF, slow-5, as well as REHO analysis revealed significant differences between two studied groups. Although results obtained with the above methods enable to identify group-specific brain structures, no overlap between the brain regions was detected. This indicates that combination of foregoing rs-fMRI methods may complement each other, revealing the bigger picture of the complex resting state abnormalities in BD.

Highlights

Bipolar disorder (BD) is a chronic and debilitating mental illness, associated with the presence of recurrent periods of depression, mania (BD type I), hypomania (BD type II), or mixed episodes
Another variant of ALFF is the fractional amplitude of low frequency fluctuations (f/ALFF), which is computed as the fractional sum of amplitudes within the low-frequency range (0.01–0.08 Hz) that was divided by the sum of amplitude across the entire frequency range [7]
Brain Sci. 2021, 11, 599 goal of this paper is to investigate the baseline brain activity in euthymic BD patients in comparison to healthy controls using a variety of Resting-state functional magnetic resonance imaging (fMRI) (rs-fMRI) analyses, such as f/ALFF, ALFF, and ALFF-based functional connectivity (FC) analysis

Summary

Introduction

Bipolar disorder (BD) is a chronic and debilitating mental illness, associated with the presence of recurrent periods of depression, mania (BD type I), hypomania (BD type II), or mixed episodes. The amplitude of low frequency fluctuations (ALFF), on the other hand, detects fluctuations lower than cardiac or respiratory ones, which are considered to be related to spontaneous neural activity within a region [6]. A recent approach called “ALFF-based FC analysis” has been proposed, which combines the aforementioned methods This technique enables evaluation of interaction and association between regional resting-state amplitude of low frequency oscillations and their network-based temporal correlations with other brain regions [8]. Another approach is to look at the respective frequencies of BOLD signal. Altered ReHo indicates changes in spontaneous neuronal activity at the local level or atypical patterns of neuronal synchrony across global networks [12]

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