Abnormal resting state EEG and vigilance in neurodegenerative dementias

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). Dementia with Lewy Bodies (DLB) is another diffuse neurodegenerative dementing disorder inducing abnormalities in vigilance (visual hallucinations, cognitive fluctuations, and REM sleep behavior disorder). These abnormalities may be reflected in the reduction in amplitude (“reactivity”) of resting‐state EEG (rsEEG) alpha rhythms (7‐9 Hz) in posterior cortical areas from eye‐closed to ‐open conditions. Indeed, this “reactivity” probes cholinergic inputs from the basal forebrain to thalamocortical mechanisms regulating vigilance. The present study tested such a hypothesis.MethodClinical and rsEEG rhythms in demographic‐ and age‐matched AD (N = 48), DLB (N = 42), and healthy cognitively unimpaired (Nold, N = 38) persons were enrolled. Pathological groups were matched as cognitive status (i.e., dementia grade). The eLORETA freeware estimated rsEEG alpha cortical sources on individual basis.ResultThere was a substantial (> ‐10%) reduction in the posterior alpha source activities from the eyes‐closed to the eyes‐open condition in 93% of the Nold seniors, 77% of the ADD patients, and 64% of the DLB patients. In these participants, there was less reactivity of the posterior rsEEG alpha source activities in the ADD and DLB groups than in the Nold group. Furthermore, there was less reactivity of the occipital rsEEG alpha source activities in the DLB than in the ADD group (p < 0.05 corrected; Figure 1).ConclusionThese novel results suggest that neurophysiological oscillatory mechanisms regulating cortical arousal in the visual system during changes in vigilance may be more abnormal in DLB than ADD patients with dementia, possibly concurring to visual misperceptions, hallucinations, and vigilance fluctuations reported in DLB patients as a function of cholinergic functional connectivity to visual cortical areas. Furthermore, the present results suggest that many DLB patients may suffer from a pathological transition from “reactive” posterior rsEEG alpha rhythms during eye‐opening to “unreactive” theta rhythms becoming a dominant background frequency. Importantly, this transition may be erroneously considered as “alpha” if the reactivity of those rsEEG rhythms is not tested during both eyes‐closed and ‐opening conditions.