Palva et al. (2010) used combined recordings of MEG and EEG to characterize phase coupled networks underlying the maintenance phase of delayed match to sample task (DMS). The inter-areal phase coupling was assessed by PLV, and statistically significant couplings were represented as undirected graphs in which vertices were the cortical areas and edges the significant couplings. Network hubs were identified by using vertex degree and betweenness centrality (graph theoretical indices). The phase coupling in alpha, beta, and gamma bands was shown to be sustained and stable throughout the visual working memory (VWM) retention period. Increasing memory load strengthened interareal coupling among the frontoparietal regions particularly strongly in the alpha band, while beta and gamma bands underlay coupling in visual regions. These observations, combined with the trend of alpha band hubs being located more frontally compared to beta and gamma band hubs, led to the suggestion that alpha band network underlies higher level attentional functions. Conversely, coupling in the beta and gamma bands were suggested to be involved in binding neuronal representations. The analysis of the most important hubs revealed that
