In the present study, we investigate the role of upper alpha oscillations for semantic access and retrieval processes. In each of a series of trials, subjects were presented trains of distorted pictures (with decreasing levels of degradation), and were asked to respond as quickly as possible when they recognize the meaning of the picture. The results show that during the time-window of picture recognition, upper alpha power decreased but inter-areal phase synchronization increased as compared to meaningless control pictures. We assume that synchronous alpha oscillations--particularly during a decrease in alpha power--reflect topographically specific neural network activity that is related to the access of semantic information in LTM.
