Brain’s default mode network may hold key to better psychiatric diagnoses


A series of studies published in recent years suggests that in people with depression, autism, schizophrenia and post-traumatic stress disorder, the default mode network, that curious pattern of brain activity that ramps up when we daydream, works differently than it does in healthy control subjects.

And in each condition, the malfunctions look slightly different, holding out the prospect of better psychiatric diagnoses down the line.

In the case of schizophrenia, researchers from Harvard University and MIT found that the default mode network is overactive and faultily wired. Writing in the Proceedings of the National Academy of Sciences in 2009, they surmised that the ability of schizophrenics to focus on and respond to external realities was being overwhelmed by their inner stream of consciousness.

In depression, the default mode network also appears to be overactive: Several brain-scan studies have shown a pattern in depression of balky transitions from introspective thought to work that requires conscious effort and frequent slippage into the default mode during cognitive tasks.

Studies show plenty of poor wiring as well. In one paper published last year, brain scans of subjects seeking first-time treatment for depression showed especially weak links between the default mode network and a region involved in motivation and reward-seeking behavior.

Wiring abnormalities also were reported in June by a group led by Dr. Marcus E. Raichle, a neurologist at Washington University in St. Louis and a pioneer in research on the default mode network. The study, in people with depression, found the default mode network to be “hot-wired” to brain regions that process emotions or help focus attention on demanding mental tasks and that connections over-fire or fire unreliably.

The excessive crosstalk among those regions might account for the common symptoms of emotional hypersensitivity and lack of concentration in depression, the authors wrote. In healthy people, attending to mental labor will suppress the default mode network, letting a person “lose himself in his work,” Raichle says. But in those with depression, he adds, the network is not so easily suppressed. There is no escape from the self.

The idea that there may be a powerful link between the brain at rest and psychiatric illness doesn’t tell us which comes first. Does too little (or too much) downtime predispose us, say, to depression? Or does corrosive depression strip our brain’s gears so that instead of engaging in more productive activities, we keep getting “stuck” in neutral?

But whichever way it is, observations like these point to a future in which psychiatrists may be able to diagnose and treat developing and full-blown mental illness by looking at how the brain idles.

“Five minutes in an fMRI scanner can yield very interesting information” on a patient, says Yale psychiatrist Godfrey Pearlson, author of a study on schizophrenia and the brain’s resting state. Pearlson speculates that for a patient impaired by delusions but not yet fully psychotic, a peek at the function of his brain in neutral could help a psychiatrist see he’s in need of early intervention.

For a patient whose ability to communicate is hampered, say, by autism, a scan of the resting brain could reveal whether a treatment already underway is working.