ABSTRACT
We report preliminary findings on EEG oscillatory correlates of working memory in mild cognitive impairment (MCI) and Alzheimer's disease (AD). Event-related desynchronization (ERD) and synchronization (ERS) of the 1-20 Hz EEG frequencies were studied using wavelet transforms in elderly controls, MCI patients and mild probable AD patients performing an auditory-verbal Sternberg memory task. Behaviourally, the AD patients made more errors than the controls and the MCI group. Statistically significant differences during the encoding of the memory set were found between the controls and the MCI group, such that the latter group showed ERD in the approximately 10-20 Hz frequencies. The findings may reflect different, compensatory encoding strategies in MCI. During retrieval, the most obvious differences were observed between the controls and the AD group: the ERD in the approximately 7-17 Hz frequencies was absent in the AD group particularly in anterior and left temporal electrode locations. This finding might indicate that AD is associated with deficient lexical-semantic processing during the retrieval phase in working memory tasks. Future studies with larger patient groups are needed to establish the diagnostic value of ERD/ERS patterns in MCI and AD.
Subject(s)
Alzheimer Disease/physiopathology , Cognition Disorders/physiopathology , Cortical Synchronization , Evoked Potentials/physiology , Verbal Learning/physiology , Acoustic Stimulation , Aged , Aged, 80 and over , Alzheimer Disease/diagnosis , Analysis of Variance , Cognition Disorders/diagnosis , Female , Humans , Male , Matched-Pair Analysis , Memory, Short-Term/physiology , Middle Aged , Reference Values , Severity of Illness Index , Statistics, NonparametricABSTRACT
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.
