Societe for Neuroscience edition:44 location:Washington DC date:15-19 November 2014
The default mode network (DMN) is a set of brain regions activated during rest in human (Shulman et al. 1997) and monkey (Mantini et al., 2011). It is engaged during internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others. In addition the DMN is hypothesized to support a broad low-level focus of attention when monitoring the external world for unexpected events (Buckner et al. 2008). 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, seemingly indifferent observation of the environment might be the glue across these conditions. If so, shifts in spatial attention should also engage the DMN. We tested this hypothesis using monkey fMRI during a covert selective attention task, previously used in humans (Molenberghs et al. 2007). Two pairs of shapes were peripherally presented and each pair contained a relevant and irrelevant shape. Monkeys fixated in the center 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 a high degree of overlap (>70%) in cortex posterior to the CS, between shift-related activations and the monkey DMN as defined in the consensus map of Mantini et al. (2011) (comparing rest vs. active task conditions in 15 expts). In contrast, shift-related activations anterior to the central sulcus, overlapped only to 8.15% with the monkey DMN, indicating possible functional subdivisions of the DMN. In the precentral sulcus and the ACC, shift- and DMN specific activations clustered adjacently. Sustained contralateral attention overlapped with the stimulus representations and activated an entirely different set of areas, except for portions of the ACC, the IPS, and area 12. Our data show that the posterior core of the DMN is clearly activated during shifting attention from one location to another, potentially mediated by frontal areas during top-down attentional control. It is therefore tempting to hypothesize that shifting operations in general, be it across memories, thoughts, and internally generated representations, are one important defining feature of the DMN. Cognitive shifting operations also break down in DMN-associated pathologies such as Alzheimer’s disease, autism and schizophrenia (Buckner et al. 2008).