The brain’s default network was originally identified in a meta-analysis that mapped brain regions more active in passive as compared to active tasks (often referred to as task-induced deactivation). The displayed positron emission tomography (PET) data include nine studies (132 participants) from Shulman et al. (1997; reanalyzed in Buckner et al. 2005). Images show the medial and lateral surface of the left hemisphere using a population-averaged surface representation to take into account between-subject variability in sulcal anatomy (Van Essen 2005). Blue represents regions most active in passive task settings.That info comes from an excellent and more technical (i.e., more useful) article than the piece below from the LA Times. This article explains the default network and its relationship to disease and is available at Scribd as a free download. Here is the abstract:
The Brain’s Default NetworkFull Citation:
Anatomy, Function, and Relevance to Disease
Randy L. Buckner, Jessica R. Andrews-Hanna, and Daniel L. Schacter
Thirty years of brain imaging research has converged to define the brain’s default network—a novel and only recently appreciated brain system that participates in internal modes of cognition. Here we synthesize past observations to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment. Analysis of connectional anatomy in the monkey supports the presence of an interconnected brain system. Providing insight into function, the default network is active when individuals are engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others. Probing the functional anatomy of the network in detail reveals that it is best understood as multiple interacting subsystems. The medial temporal lobe subsystem provides information from prior experiences in the form of memories and associations that are the building blocks of mental simulation. The medial prefrontal subsystem facilitates the flexible use of this information during the construction of self-relevant mental simulations. These two subsystems converge on important nodes of integration including the posterior cingulate cortex. The implications of these functional and anatomical observations are discussed in relation to possible adaptive roles of the default network for using past experiences to plan for the future, navigate social interactions, and maximize the utility of moments when we are not otherwise engaged by the external world. We conclude by discussing the relevance of the default network for understanding mental disorders including autism, schizophrenia, and Alzheimer’s disease.
Buckner, R.L., Andrews-Hanna, J.R. & Schacter, D.L. (2008). The brain’s default network: Anatomy, function, and relevance to disease. Annals of the N.Y. Academy of Sciences. 1124: 1–38 (2008). doi: 10.1196/annals.1440.011
Here is the LA Times piece, which is a pretty good basic introduction to the ideas in the longer article:
Division of duty is the name of the brain game
Crisis management takes a village — a skull-centric, multi-tasking village called the default-mode network.
You may be lazing by the pool after a visit or two to the swim-up bar, but parts of your brain are always on duty — ready to leap into action should a stressful event require attention.May 30, 2011
This skeleton crew of sorts is called the default-mode network.It includes one of the busiest and most important structures in the entire brain, the hippocampus, which is responsible for processing memories. "Whenever you have to look something up or file something away, you ask your hippocampus to do it," says Jens Pruessner, an associate professor in the departments of psychology, psychiatry, neurology and neurosurgery at McGill University in Montreal.
It also includes the medial orbitofrontal cortex, an area involved with self-referential thoughts, and the anterior cingulate, which Pruessner calls an "error monitor.... Its job is to stay on guard for mismatches between what you expect to happen and what actually happens."
So, for example, suppose it's the first night of your vacation and you're at a karaoke bar, and your medial orbitofrontal cortex is busy thinking that maybe you should get up and sing a little. But then your killjoy hippocampus dredges up some memories of the last time you sang karaoke, causing your medial orbitofrontal cortex to start having second thoughts.
But then, before anything gets decided about your performing career, a stranger passing by trips over your chair and spills his drink on your head. Your anterior cingulate was not expecting that! So it quickly files an error report with your stress-response system and turns itself off temporarily so all your brainpower can concentrate on this critical situation. And your medial orbitofrontal cortex realizes that your brain has better things to do right now than to think about your musical talents, or lack thereof, so it turns itself off temporarily too.
Meanwhile, your hippocampus, as part of its endless job of filing away new information, stores the information that something wet has just fallen on your head. But because this is a little out of the ordinary and your hippocampus recognizes it as a possible source of stress, it puts on another of its many hats. "It's the secretary for all things memory," Pruessner says, "but it also has its hand on the button to turn on your stress response."
As soon as it pushes that button, the hippocampus also shuts itself down and waits while the response system arranges for your adrenal glands to release some cortisol. "The cortisol gives you additional energy to withstand this new stress," Pruessner says. As soon as there's enough of the hormone in circulation, the hippocampus turns itself back on.
Still, for the short time that it's offline, from seconds to minutes, you may not be quite as clever as usual. Which is why, although the perfect witty remark to make to the drink-spiller will surely come to you, that may not happen until you're back in your hotel room.
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