What is your brain doing when you’re just relaxing, staring into space?
Traditionally, when scientists think about brain function, they focus on its more obvious actions: feeling emotions, solving problems. That makes sense: aren’t we all most interested in what our all-too-human brains do? Adventurous neuroscientists have set up all manner of functional MRI experiments in which they put people in a scanner, then show photos of happy or sad faces, or get them to recall moments of trauma and loss. Even to address moral dilemmas: a trolley rolling down a track, about to run over either one of your loved ones or half a dozen strangers: which way will you turn the switch?
Not surprisingly, these studies come up with incredible pictures showing that particular parts of the brain activate when you re-experience trauma or see a beautiful face--and even by your effort to make a moral choice.
The problem is, such findings are often difficult to interpret. Results vary from one MRI machine to another, from one research group to the next. Also, there’s the question of cause and effect. When a particular brain center lights up, it‘s often difficult to know whether it is essential in processing a stimulus, or whether it just reflects more important activity going on elsewhere.
In contrast, when we daydream, apparently doing nothing, our brains have characteristic patterns of activity--which are actually very reproducible from one study to the next, between scanners and studies and investigators.
Daydreaming is, counterintuitively, an incredibly active brain state. Just close your eyes, let your mind wander, and the medial temporal lobe starts to chatter up a storm with the medial prefrontal cortex and the posterior cingulate cortex. What’s the function of all this activity? Perhaps to generate ideas, to integrate thoughts with experiences, or to consolidate memories--but it seems to be an essential aspect of normal brain functioning.
Just a few minutes in the MRI scanner--with the instruction, “just relax and lie still”--are sufficient to activate this Default Mode Network (DMN). Perhaps not surprisingly, people with depression, schizophrenia, and autism have very different patterns of default mode brain activity than the rest of us. In schizophrenia, for example, researchers believe that overactivity of the DMN makes it difficult to concentrate on the outside world, because of an excessive focus on internal realities.
In depression, likewise, there is increased DMN activity between certain brain centers, including the ventromedial prefrontal cortex, the anterior cingulate, and the lateral temporal cortex. The depressed brain appears to be particularly active in areas related to ‘self-referential processing’ or ruminations. It may have difficulty turning off DMN activity to focus on solving problems or to pay attention to others.
In a sense, depression may be an inability to stop mind-wandering!
These recent DMN findings fascinate me as both as a researcher and as a practicing psychiatrist.
As a researcher, DMN is appealing because it’s eminently practical. It doesn’t take long to do DMN testing: only a few minutes in a scanner (though it does take awhile to process the images). And since results are ‘reproducible’ from one scanner to the next, once you analyze them, you can be fairly confident that you’re measuring a real signal.
In fact, my research group at Columbia and the New York State Psychiatric Institute just recently finished a DMN study in people with chronic depression, both before and after treatment with antidepressant medicine or placebo. We are still analyzing our data, but hopefully we can answer whether chronic low-grade depression also shows increased DMN activity--similar to more severe major depression--and whether medicine quiets these hyperactive circuits.
But these questions also fascinate me as a practicing psychiatrist. As a doctor, I can’t help but think that my patients’ brains run differently when they’re depressed than when they’re feeling good...and that their brains differ from brains of people who have never been depressed.
With patients I often use the analogy that the depressed brain is like a car that isn’t properly tuned, its engine idling too fast, wasting gas; and that medication or therapy is a type of tuneup, correcting the mix of oxygen and gasoline, lowering the idle speed to normal. It’s a crude metaphor, true, but DMN research makes me think there may be something to it.
Like many psychiatrists, I often recommend that my depressed patients start meditating. Once they do that, they often get better at managing their moods, and become notably more able to calm themselves without Xanax. I’m particularly impressed how mindfulness techniques can help depressed people to stop their churning ruminations and to begin focusing calmly on the here and now. For a long time I’ve been willing to bet that meditation decreases DMN activity!
Then, just a few weeks ago I came across a fascinating study, by Judson Brewer and colleagues at Yale, looking at the effect of meditation on the DMN. Brewer found that the DMN is indeed different for experienced meditators, who have less activity in the main nodes of the DMN, including the medial prefrontal and posterior cingulate cortex. Beyond that, meditators had stronger connections between brain regions “previously implicated in self-monitoring and cognitive control”--both at rest and during meditation. They were able to change the activity of their default mode networks in a way consistent with decreased mind-wandering.
Of course, some mind-wandering is productive and creative, rather than destructive and self-sabotaging. My guess is that experienced meditators are able to do more of the former and to turn off the latter.
So that’s why I’m so excited about the DMN. Among other things, DMN research can open up new avenues to study the physiology of disorders and to find better treatments, including ‘complementary modalities’ like exercise and meditation. Beyond that, DMN research gives us new respect for the value--and potential dangers--of mind-wandering!