The abnormalities found in alpha oscillations in the parieto-occipital regions in patients with AD were more prominent over the medial parietal cortex, particularly in the precuneus, while the reduced alpha oscillations in patients carrying the APOE-4 allele compared with noncarriers had higher maxima in the inferior parietal cortex. Of note, these two regions of the parietal lobe are part of the DMN, a brain circuit typically active during rest [37]. The alpha rhythm or enhanced alpha activity in posterior regions is one of the most prominent electromagnetic changes in the human brain, representing a distinctive feature of the normal brain in the waking resting-state. Abnormalities in alpha power or its typical parieto-occipital distribution may sometimes represent an early or the only sign of cerebral dysfunction in neuropsychiatric disorders [61]–[64]. In addition, it is well established that patients with AD present with clinical symptoms of temporal (e.g., memory impairment) and parieto-occipital deficits (e.g., visuospatial impairment) even at early stages of the disease [1], [13]. Therefore, the reduction in alpha power found in patients with AD in this study, along with a tendency towards an increase in slow oscillatory activity most likely represents disease- and genotype-related resting-state regional dysfunction.
