Let's Talk Together: Memory Traces Revealed by Cooperative Activation in the Cerebral Cortex

Abstract

Publisher Summary This chapter provides an overview of magnetoencephalography (MEG) studies of different types of memory processes. The analysis of event-related magnetic fields (ERFs) has supported the involvement of temporo-parieto-frontal networks in visual long-term memory and added knowledge about the temporal dynamics of these activations. During working memory, a common finding has been increased ERF amplitude generated by parieto-prefrontal sources during the ∼300 to 600 ms after presentation of the stimulus that was to be encoded. The major part of this chapter focuses on cortical oscillatory activity as a correlate of working memory. Several studies have implicated activity in the theta (4 to 8 Hz) and gamma (∼30 to 100 Hz) bands in memory processing. Oscillatory activity, particularly in the higher frequency ranges, is thought of as a signature of the synchronous activation of distributed cortical networks. Studies investigating passive auditory deviance processing revealed increased gamma-band activity (GBA) over anterior temporal/inferior frontal areas during auditory pattern mismatch and over posterior temporo-parietal cortex during auditory spatial mismatch processing. The same regions were involved in the maintenance of spatial sound features and auditory patterns during short-term memory tasks. In addition, prefrontal GBA increases characterized short-term memory for both types of stimuli. Gamma phase synchronization between the auditory stream areas (possible higher sensory storage systems) and prefrontal cortex (putative central executive system) was enhanced throughout the memorization phases.