One would hope that, by starting from the beginning, the central

One would hope that, by starting from the beginning, the central issues will become clearer to the student or clinician interested in the topic. As such, this piece is not a comprehensive review, so it is recommended that readers explore several related reviews for a more thorough analysis.3-5 For those interested in a detailed historical account see refs 11 and 1211,12. The present piece will be especially useful to readers interested in a broad understanding of how the concept of the find more default network arose and how its discovery relates to contemporary research emphases. Origins of discovery

and implications The default network was discovered serendipitously when investigators began noticing that specific, Inhibitors,research,lifescience,medical reproducible brain regions were more active during passive control tasks than during active tasks targeted by the experimenters.6,7 In many instances,

Inhibitors,research,lifescience,medical responses in the passive (control) tasks were not reported, or were reported with minimal discussion. In one of our first studies of memory we noticed that a broad network of regions was active in the passive control task, during which participants simply fixated a crosshair. However the network was Inhibitors,research,lifescience,medical paradoxically less active in the targeted task, in which participants generated words.13 In an insightful anticipation of later work on the default network, Andreasen et al observed that passive tasks showed activation in regions that were also active when individuals recalled information from episodic memory.8 In an intentionally ironic twist, they labeled the passive “rest” condition “Random Episodic Silent Thinking” and suggested that “free-ranging mental activity (random episodic memory) produces

large activations in association cortex and may reflect Inhibitors,research,lifescience,medical both active retrieval of past experiences and planning of future Inhibitors,research,lifescience,medical experiences.” They further argued that the regions involved were specifically regions of association cortex that “are more highly developed (ie, comprise a larger portion of the brain volume) in human beings than in nonhuman primates or other animals, have the most complex columnar cortical organization, and are the last to myelinate. Apparently, when the brain/mind thinks in a free and unencumbered fashion, it uses its most human and complex parts” (p1583). The manner in which the default network was initially identified has ADP ribosylation factor had a lasting impact on how we think about its function and discuss the phenomena associated with the network. In typical task settings, the default network is most active in passive control tasks where the experimenter’s demands required are minimized. The observation that the default network is active in passive tasks has led to a split in ideas about its functions. In one class of ideas, the network is seen as playing a role in the exploratory, unfocussed state that takes place during passive tasks.

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