Alpha band disruption in the AD-continuum starts in the Subjective Cognitive Decline stage: a MEG study

Abstract

The consideration of Subjective Cognitive Decline (SCD) as a preclinical stage of AD remains still a matter of debate. Alpha band alterations represent one of the most significant changes in the electrophysiological profile of AD. In particular, AD patients exhibit reduced alpha relative power and frequency. We used alpha band activity measured with MEG to study whether SCD and MCI elders present these electrophysiological changes characteristic of AD, and to determine the evolution of the observed alterations across AD spectrum. The total sample consisted of 131 participants: 39 elders without SCD, 41 elders with SCD and 51 MCI patients. All of them underwent MEG and MRI scans and neuropsychological assessment. SCD and MCI patients exhibited a similar reduction in alpha band activity compared with the no SCD group. However, only MCI patients showed a slowing in their alpha peak frequency compared with both SCD and no SCD. These changes in alpha band were related to worse cognition. Our results suggest that AD-related alterations may start in the SCD stage, with a reduction in alpha relative power. It is later, in the MCI stage, where the slowing of the spectral profile takes place, giving rise to objective deficits in cognitive functioning.

Biomagnetic biomarkers for dementia: A pilot multicentre study with a recommended methodological framework for magnetoencephalography

“…In general, we confirmed the slowing in oscillatory power and reduction in the peak frequency of the alpha band in patients, which are robust features of MCI and AD [19][20][21]. This pattern, particularly the increase in low-frequency power in the MCI group, was common across all three analyses, despite their differences in using normalized versus raw power, sensor versus source-space and different spectral estimators.…”

“…Artifact-related components were removed. MEG data were segmented into 4-second epochs and filtered using a 2000th order FIR band-pass filter with a Hanning window into five bands (with 2 seconds of real data padding added either side): for source analysis: broad band (2-45 Hz), and for connectivity analysis: theta (4-8 Hz), alpha (8-12 Hz), beta (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and gamma (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45). The data were coregistered to the T1-weighted MRI and the forward model calculated using a realistic single shell head [11].…”

Functional neuroimaging in subjective cognitive decline: current status and a research path forward

“…Multifaceted patterns of increased and decreased connectivity between regions could reflect breakdown in processing within a subnetwork that shifts processing load to more intact components of the broader network. Diffuse and frontally localized MEG alpha band power reductions have also been noted in older adults with SCD [39,46], without group differences in the small world properties of theta and beta bands [58]. Moreover, lower subgraph centrality (a measure of weighted, closed walks starting and ending at a node, representing mid-scale connectivity) has been observed in occipital and paracentral regions in older adults with SCD [48].…”

Age and APOE genotype affect the relationship between objectively measured physical activity and power in the alpha band, a marker of brain disease.

“…Power in the alpha band has been the focus of attention in many studies targeting different stages of preclinical and prodromal AD, as well as clinically symptomatic AD. Alterations of this kind of activity have been detected in asymptomatic ε4 carriers (Frutos-lucas et al, 2018), in individuals with subjective cognitive decline (SCD) (López-Sanz et al, 2016) and mild cognitive impairment (MCI) (Garcés et al, 2013), and correlate with cognitive worsening. Power reduction in the alpha band is thought to be the result of cumulative synaptic damage, mostly of cholinergic connections, which impedes the synchronization of activity at higher frequencies (Ebert and Kirch, 1998;Osipova et al, 2005).…”