EEG-alpha rhythms and memory processes.

The results of several experiments indicate that alpha frequency varies as a function of memory performance. It was found that in samples of age matched subjects alpha frequency of good memory performers is about 1 Hz-higher than those of bad performers. The difference in alpha frequency between good and bad performers reaches a maximum during the retrieval of information, is much smaller during encoding and is minimal--but still significant--during a resting period. These results suggest that alpha frequency may be a permanent and not only a functional parameter that determines the speed with which information can be retrieved from memory. The calculation of changes in band power indicate further that the upper alpha band is particularly sensitive to semantic memory demands. The lower alpha band, on the other hand, seems to reflect attentional processes. These findings are discussed on the basis of a hypothesis which assumes that EEG frequencies within the alpha band stem at least in part from the thalamus and that the activity of thalamo-cortical networks reflects processes that are related to searching, accessing and retrieving information from (scmantic) long-term memory.