Here, we discuss relevant literature findings on abnormal resting-state scalp-recorded electroencephalographic (rsEEG) rhythms in old patients with severe cognitive deficits and disabilities in activities of daily living (i.e., dementia) due to Alzheimer’s (ADD), Parkinson’s (PDD), and Lewy body (DLB) neurodegenerative diseases. Furthermore, we described a modern quantitative EEG (qEEG) methodology to explore those rhythms and related vigilance disorders.

The reviewed findings unveil consistent abnormalities in topographic and frequency (most in <12 Hz) features of the rsEEG rhythms recorded in ADD, PDD, and DLB patients, probably reflecting altered neurophysiological oscillatory mechanisms of synchronization and functional connectivity in neural brain populations underpinning the regulation and maintenance of the quiet vigilance. The proposed qEEG methodology showed significant differences in the posterior cortical sources of rsEEG alpha rhythms at individual frequencies among small groups of ADD, PDD, and DLB patients.

Although the above abnormalities may have a limited diagnostic value at the individual level, not specifically reflecting the neuropathological processes underlying ADD, PDD, and DLB, they have significant heuristic and clinical relevance. Namely, the rsEEG readouts at the alpha frequencies unveiled the altered neurophysiological oscillatory mechanisms responsible for vigilance disorders in ADD, PDD, and DLB patients and may be used as pathophysiological biomarkers to evaluate the efficacy of (non)pharmacological interventions to treat those disorders.

We recommend using the present qEEG methodology in longitudinal rsEEG studies carried out in ADD, PDD, and DLB patients to explore the abnormalities in the rsEEG biomarkers of vigilance dysregulations during the disease progression.