Cortical arousal is differently related with resting‐state electroencephalographic delta rhythms in healthy seniors and in patients with dementia due to Alzheimer’s disease

Abstract

AbstractBackgroundKeeping in mind Başar’s theory of event‐related EEG oscillations, here we hypothesize that transient increases in delta rhythms in quiet wakefulness may enhance global cortical arousal as revealed by the desynchronization of alpha rhythms in normal (Nold) seniors with some derangement in Alzheimer’s disease dementia (ADD).MethodClinical and EEG datasets in 100 ADD and 100 Nold individuals matched as demography, education, and gender were taken from an international archive. Standard delta (< 4 Hz) and alpha1 (8‐10.5 Hz) bands were used for the main analysis, while alpha2 (10.5‐13 Hz), theta (4‐8 Hz), beta1 (13‐20 Hz), beta2 (20‐35 Hz), and gamma (35‐40 Hz) served as controls. In the interpretation, the higher the alpha1 power (density), the lower that arousal.ResultAs expected, when compared to the Nold group, the ADD group showed higher global (scalp) power density at the delta‐theta band and lower global power density at the alpha‐beta bands. As novel findings, we observed that: (1) in the Nold group, the global delta and alpha1‐2 power were negatively and linearly correlated; (2) in the ADD group, this correlation was just marginal; and (3) in both Nold and AD groups, the EEG epochs with the highest delta power (median value for stratification) were associated with the lowest voxel‐based eLORETA solutions at the alpha1 band (i.e., eLORETA alpha1 current density at 8‐10.5 Hz). In the Nold group, the maximum t values of the differences between DELTA+ and DELTA‐ were localized in the occipital Brodmann area (BA) 18 at the Talairach coordinates X = 0, Y = −100, and Z = 5 (p < 0.05 corrected; Figure 1). In the ADD group, those maximum t values were instead localized more anteriorly, namely in the central BA 6 at the Talairach coordinates X = 40, Y = −10, and Z = 45 (p < 0.05 corrected; Figure 2).ConclusionThese results suggest that even in quiet wakefulness, delta and alpha rhythms are related to each other, and ADD partially affects this cross‐band neurophysiological mechanism.