Relationship between default mode network and posterior resting‐state electroencephalographic delta rhythms in cognitively unimpaired seniors and patients with dementia due to Alzheimer’s

Abstract

AbstractBackgroundAlzheimer’s disease dementia (ADD) is the most common neurodegenerative dementing disorder explaining about 60‐70% of 50 million patients worldwide (www.who.int). Some previous studies in ADD patients showed significant neurodegenerative processes as revealed by reduced gray matter volume in the cerebral cortex, including the default mode network (DMN), dorsal attention (DAN), and sensorimotor (SMN) cortical networks from structural magnetic resonance imaging (sMRI). Other studies in these patients reported the “slowing” of the resting‐state eyes‐closed electroencephalographic (rsEEG) rhythms reflecting vigilance dysfunctions. Here we tested the hypothesis of a significant relationship between these neurodegenerative and neurophysiological readouts, thus suggesting the sensitivity of rsEEG activity to intrinsic AD processes.MethodClinical, sMRI, and rsEEG rhythms in demographic‐ and age‐matched ADD (N = 45) and healthy cognitively unimpaired (Nold, N = 40) persons were available from an international archive (www.pdwaves.eu). Individual alpha frequency peak was used to determine the alpha frequency band on a personal basis. Fixed beta bands were considered. The eLORETA freeware estimated rsEEG sources in posterior (i.e., central, parietal, and occipital) cortical regions of interest. Freeware platforms served to estimate the normalized gray matter volume in the DMN, DAN, and SMN cortical networks from sMRI.ResultThe results (Fig. 1) showed: (1) lower DMN, DAN, and SMN volumes (maximum effects in the DMN), higher posterior rsEEG delta‐theta source activities, and lower rsEEG alpha source activities in the ADD than in the Nold group; (2) substantial inverse correlation between the DMN volume and the posterior rsEEG delta‐theta source activities in the ADD and Nold participants; and (3) a mediating effect of the posterior rsEEG delta‐theta source activities in the correlation between the DMN volume and the global cognitive status across all participants.ConclusionThese results suggest a prominent relationship between DMN atrophy and the posterior rsEEG delta‐theta rhythms across physiological and AD‐related aging. As such, they support the enrichment of the ATN model for an extension to “Physiology” (P) = A‐T‐P‐N, as the physiology of the oscillatory activity within large inter‐connected neuronal populations due to disruptive effects of AD‐related neuropathology can be additionally informative.