Reactivity of posterior cortical electroencephalographic alpha rhythms during eyes opening in cognitively intact older adults and patients with dementia due to Alzheimer's and Lewy body diseases

•Nold, ADD and DLB subjects show a reduction in the posterior rsEEG alpha activities at the eyes-opening.•Compared to Nold, ADD and DLB subjects show less reactivity of the posterior alpha source.•Compared to ADD, DLB subjects show less reactivity of the posterior alpha source.