Control mechanisms in working memory: A possible function of EEG theta oscillations

Neural correlates of control mechanisms in human working memory are discussed at two levels in this review: (i) at 'item level', where in multi-item working memory information needs to be organized into sequential memory representations, and (ii) at a 'process level', indicating the integration and control of a variety of cognitive functions involved in working memory, independent of item representations per se. It will be discussed that at both levels electroencephalographic theta activity is responsible for control of working memory functions. On item level, exact phase coding, e.g., approached by coupling between theta and gamma oscillations or phase resetting of theta frequency, is suggested to integrate information into working memory representations. At process level interregional theta synchronization is discussed to integrate brain structures necessary for working memory. When discussing the specificity of theta activity for control of working memory processes it will be suggested that theta oscillations might play an important general integrative role in organization of brain activity. And as working memory often involves a variety of cognitive processes which need to be coordinated there is particular need for an integrative brain mechanism like theta activity as suggested in this review. (C) 2009 Elsevier Ltd. All rights reserved.