Early Changes in Alpha Band Power and DMN BOLD Activity in Alzheimer's Disease: A Simultaneous Resting State EEG-fMRI Study.

Katharina Brueggen,Christoph Berger,Stefan J Teipel,Carmen Fiala,Sina Ochmann,Claudio Babiloni

doi:10.3389/fnagi.2017.00319

Abstract

Simultaneous resting state functional magnetic resonance imaging (rsfMRI)–resting state electroencephalography (rsEEG) studies in healthy adults showed robust positive associations of signal power in the alpha band with BOLD signal in the thalamus, and more heterogeneous associations in cortical default mode network (DMN) regions. Negative associations were found in occipital regions. In Alzheimer’s disease (AD), rsfMRI studies revealed a disruption of the DMN, while rsEEG studies consistently reported a reduced power within the alpha band. The present study is the first to employ simultaneous rsfMRI-rsEEG in an AD sample, investigating the association of alpha band power and BOLD signal, compared to healthy controls (HC). We hypothesized to find reduced positive associations in DMN regions and reduced negative associations in occipital regions in the AD group. Simultaneous resting state fMRI–EEG was recorded in 14 patients with mild AD and 14 HC, matched for age and gender. Power within the EEG alpha band (8–12 Hz, 8–10 Hz, and 10–12 Hz) was computed from occipital electrodes and served as regressor in voxel-wise linear regression analyses, to assess the association with the BOLD signal. Compared to HC, the AD group showed significantly decreased positive associations between BOLD signal and occipital alpha band power in clusters in the superior, middle and inferior frontal cortex, inferior temporal lobe and thalamus (p < 0.01, uncorr., cluster size ≥ 50 voxels). This group effect was more pronounced in the upper alpha sub-band, compared to the lower alpha sub-band. Notably, we observed a high inter-individual heterogeneity. Negative associations were only reduced in the lower alpha range in the hippocampus, putamen and cerebellum. The present study gives first insights into the relationship of resting-state EEG and fMRI characteristics in an AD sample. The results suggest that positive associations between alpha band power and BOLD signal in numerous regions, including DMN regions, are diminished in AD.

Highlights

In Alzheimer’s disease (AD), resting state functional magnetic resonance imaging, and resting state electroencephalography have only been used separately to measure pathological changes
Patients were recruited via the memory clinic at the University Medicine Rostock (UMR); healthy controls (HC) subjects were recruited via the database of the UMR, containing healthy subjects who were originally recruited via advertisement
At visual inspection, a morphological difference in the form of dysmorphic alpha waves was observed in the AD group

Summary

Introduction

In Alzheimer’s disease (AD), resting state functional magnetic resonance imaging (rsfMRI), and resting state electroencephalography (rsEEG) have only been used separately to measure pathological changes. The alpha band is the dominant rhythm in healthy adults during a state of relaxed wakefulness, keeping the eyes closed (Berger, 1929; Zschocke and Hansen, 2012; Hinrichs, 2015) It originates from thalamo-cortical neurons projecting to the occipital cortex (Lorincz et al, 2009; Hughes et al, 2011; Zschocke and Hansen, 2012; Babiloni et al, 2015) – a projection pathway that may be disrupted in AD, as shown previously in studies using a computational model (Bhattacharya et al, 2011) and fMRI functional connectivity (Zhou et al, 2013). Power within the alpha band has been shown to correlate negatively with hemodynamic activity in the occipital cortex (Goldman et al, 2002; Moosmann et al, 2003; Gonçalves et al, 2006; Mantini et al, 2007; Scheeringa et al, 2012)

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