The electrophysiological basis of the default mode network
Nearly half of the cortical surface is metabolically active at rest, and yet the function and neural dynamics of this network in various cognitive states is not well established. Elucidating the function and spatiotemporal dynamics of this ‘default mode’ network (DMN) can provide critical insight into internally-directed thought processes as well as the pathology of common neurological diseases. Here, we measured electrical activity directly from the cortical surface in eight patients undergoing epilepsy monitoring for surgical resection in order to examine the neural representation of the DMN at rest and in response to sensory and electrical stimulation. We first demonstrate that the DMN exhibits tight coupling of slow fluctuations of power in the high gamma (70-150Hz; HGP) frequency band. Next, we show that electrical stimulation evokes strong cortico-cortical responses within and between anatomically disparate nodes of the DMN. Finally, we demonstrate that task-related decreases in HGP are the most prevalent response within the DMN, yet account for only half of all task-related HGP decreases in the brain. Taken together, these findings suggest that the DMN represents an electrophysiological phenomenon consisting of tightly interconnected regions that become suppressed during goal-directed processes.