EVENT-RELATED DESYNCHRONIZATION IN THE ALPHA-BAND AND THE PROCESSING OF SEMANTIC INFORMATION

The hypothesis was tested whether event-related power shifts in the up per alpha band are specifically related to semantic memory processes. In Expt. 1 subjects had to judge whether pairs of sequentially present ed words (W1-W2) were semantically congruent. In the following experim ents subjects were presented the W1 words of Expt. 1 and were asked to perform a free association task in Expt. 2 and a cued recall task in Expt. 3. It is assumed that semantic memory demands dominate in Expt. 1, whereas working memory demands dominate in Expt. 3 and that Expt. 2 takes an intermediate position with respect to both types of task dem ands. A significant task-related power change that responds selectivel y to semantic processing demands was found for the upper alpha band an d over the left side of the scalp. The lower alpha band, on the other hand, most likely reflects unspecific processing demands such as atten tion. A more general interpretation of these findings is that differen t cognitive processes such as semantic memory, perceptual encoding and attentional processes are reflected by band power changes in differen t and rather narrow frequency bands over localized regions in the brai n. (C) 1997 Elsevier Science B.V.