Similarities appear in regard to cognitive functioning and suggest beta-band synchronization may also correspond to a cognitive idling rhythm. Non-human primate studies have shown that synchronization in the beta-band is strongest during tasks requiring a high degree of endogenously-driven attention and lowest on tasks requiring processing of novel or unexpected external events [59, 60]. Engel and Fries [52] suggest that strong beta-band synchronization across a neuronal population promotes the maintenance of a motor or cognitive state because the signal of this neuronal assembly overrides any signals coming from new inputs. Building on this, they suggest that the DMN should be distinguished by prominent beta-band synchronization, since it constitutes a state characterized by low expectation of change. Indeed, several studies have revealed positive associations between absolute beta-band power and BOLD signal change in the DMN [5, 61–63]. In the context of our findings, the elevated beta-band synchronization involving DMN regions in the MDD group may reflect highly synchronized neuronal populations, the signal from which is processed at the expense of other inputs that signal the need to flexibly modulate the DMN
