Temporal and spectral signatures of the default mode network

The existence of a structured pattern of neuronal activity in the brain at rest has been consistently reported in the neuroscience literature. Multiple techniques, such as fMRI, MEG and EEG, showed that spontaneous, slow fluctuations of cerebral activity are temporally coherent within distributed functional networks resembling those evoked by sensory, motor, and cognitive paradigms. Among these networks, the Default Mode network gained large interest because of its anatomical and functional architecture. In fact, this network seems to reflect the default brain activity at rest and it has been associated with internal mentation, autobiographical memory, thinking about one's future, theory of mind, self-referential and affective decision making. What processing demands are shared in common across such a variety of tasks is presently unclear, and to disentangle such high level tasks into component processes is challenging. Here, we address some of these aspects by reviewing the current MEG studies on this network. In fact, while MEG data confirm the observed fMRI spatial topography, some new intriguing temporal and frequency properties of this network are revealed. Such findings enrich the original fMRI scenario on the DMN functional roles in terms of internal coupling and cross-network communication in the brain at rest. The Default Mode Network's internal coupling seems to be characterized by slow frequencies in the alpha and beta range and the cross-network interaction reveals that the DMN plays a central role in the communication across many different resting state networks.