Effects of normal aging on event-related desynchronization/synchronization during a memory task in humans.

Event-related desynchronization (ERD) and event-related synchronization (ERS) of the 1-20Hz EEG frequencies were studied using wavelet transforms in young (n = 10, mean age 22) and elderly subjects (n = 10, mean age 65) performing an auditory Sternberg memory task with words as stimuli. In both age groups, encoding of the four-word memory set elicited ERS in the theta and alpha frequency range. Theta ERS, and ERD in the alpha and beta bands were observed during retrieval. During encoding, the elderly showed greater alpha ERS and smaller theta ERS. During retrieval, smaller alpha ERD and theta ERS was found in the elderly subjects. Also, in the elderly, beta ERD was elicited in the late time window during retrieval. The statistically significant differences between the age groups were more marked during retrieval than during encoding. The results indicate that although the two groups performed equally well behaviorally in the task and the elderly subjects were cognitively intact, normal aging affects oscillatory theta, alpha and beta responses particularly during retrieval from working memory. The ERD/ERS patterns of the elderly resemble those of children found in a recent study, which might suggest that those memory-related brain processes that evolve later in childhood are the first to be affected in older age.