The Brain Machinery Behind Daydreaming

New research shows how our brains make—and profit from—wandering thoughts

By Alison Gopnik

Like most people, I sometimes have a hard time concentrating. I open the file with my unwritten column and my mind stubbornly refuses to stay on track. We all know that our minds wander. But it’s actually quite peculiar. Why can’t I get my own mind to do what I want? What subversive force is leading it astray?

A new paper in Nature Reviews Neuroscience by Kalina Christoff of the University of British Columbia and colleagues (including the philosopher Zachary Irving, who is a postdoctoral fellow in my lab) reviews 20 years of neuroscience research. The authors try to explain how our brains make—and profit from—our wandering thoughts.

When neuroscientists first began to use imaging technology, they noticed something odd: A distinctive brain network lighted up while the subjects waited for the experiment to begin. The scientists called it “the default network.” It activated when people were daydreaming, woolgathering, recollecting and imagining the future. Some studies suggest that we spend up to nearly 50% of our waking lives in this kind of “task-unrelated thought”—almost as much time as we spend on tasks.

Different parts of the brain interact to bring about various types of mind-wandering, the paper suggests. One part of the default network, associated with the memory areas in the medial temporal lobes, seems to spontaneously generate new thoughts, ideas and memories in a random way pretty much all the time. It’s the spring at the source of that stream of consciousness.

When you dream, other parts of the brain shut down, but this area is particularly active.

Neuroscientists have recorded in detail rats’ pattern of brain-cell activity during the REM (rapid eye movement) sleep that accompanies dreaming. Rat brains, as they dream, replay and recombine the brain activity that happened during the day. This random remix helps them (and us) learn and think in new ways.

Other brain areas constrain and modify mind-wandering—such as parts of our prefrontal cortex, the control center of the brain. In my case, this control system may try to pull my attention back to external goals like writing my column. Or it may shape my wandering mind toward internal goals like planning what I’ll make for dinner.

Dr. Christoff and colleagues suggest that creative thought involves a special interaction between these control systems and mind-wandering. In this activity, the control system holds a particular problem in mind but permits the brain to wander enough to put together old ideas in new ways and find creative solutions.

At other times, the article’s authors argue, fear can capture and control our wandering mind. For example, subcortical emotional parts of the brain, like the amygdala, are designed to quickly detect threats. They alert the rest of the brain, including the default network. Then, instead of turning to the task at hand or roaming freely, our mind travels only to the most terrible, frightening futures. Fear hijacks our daydreams.

Anxiety disorders can exaggerate this process. A therapist once pointed out to me that, although it was certainly true that the worst might happen, my incessant worry meant that I was already choosing to live in that terrible future in my own head, even before it actually happened.

From an evolutionary point of view, it makes sense that potential threats can capture our minds—we hardly ever know in advance which fears will turn out to be justified. But the irony of anxiety is that fear can rob us of just the sort of imaginative freedom that could actually create a better future.

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