Differences in EEG harmonic driving responses to photic stimulation between normal aging and Alzheimer's disease

In order to investigate whether Alzheimer's disease (AD) is the end result of aging of the brain or the result of some other mechanism, we analyzed EEGs showing the absolute power of harmonic responses to photic stimulation (PS) in younger subjects, non-demented elderly subjects and AD patients. At rest, the AD patients generally showed less absolute power than the younger and elderly subjects, with significant differences found at 10Hz and 20Hz. Analysis of EEGs recorded during PS indicated that the elderly subjects generally demonstrated more absolute power than the younger subjects and AD patients. These findings suggest a failure of stimulation-related brain activation in AD patients, and provide further evidence that normal aging and AD employ different mechanisms for functional organization during PS.