The DMN is a set of regions being activated during rest. It is engaged during internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving others' perspectives. It is also hypothesized to support a broad low-level focus of attention when monitoring the external world for unexpected events. Defining an overarching function common to such widely different conditions, however, is implicitly difficult. An intriguing possibility is that "shifting operations" between series of internal thoughts, memories, and during passive observations of the environment might be the glue across these conditions. If so, shifts in selective spatial attention should also engage the DMN. We tested this hypothesis using monkey fMRI during a challenging covert selective attention task, previously used in humans. Two pairs of shapes were peripherally presented, each containing a relevant and irrelevant shape. Monkeys fixated and had to respond manually when the relevant stimulus dimmed. An event consisted of the replacement of the current stimulus pair by the other pair. In 1/3 of the trials this change between pairs elicited a spatial shift in attention as the relevant stimulus was replaced by an irrelevant one.
An event-related analysis (N=3) revealed an exceedingly high degree of overlap (97.2%) between shift-related activations and the DMN. Sustained contralateral attention activated an entirely different set of areas, except for portions of ACC, IPS, and area 12.
Our data show that the DMN is activated during a very specific cognitive operation (shifting attention from one location to another). It is therefore tempting to hypothesize that shifting operations in general, be it across memories, thoughts, and internally generated representations, are an important defining feature of the DMN. Cognitive shifting operations also break down in DMN-associated pathologies such as Alzheimer's disease, autism and schizophrenia.