Does a Resting Mind Correspond to the Brain's Default Mode?
Specific neural areas become active in fMRIs while the wakeful mind is resting.
Posted Aug 31, 2015
It's remarkable that "The world is too much with us" launched its poetic complaint about the hectic pace of life in 1807, long before 24-hour news, intrusive cell phones, and dystopian airports made it even more vital to pause for downtime. A relaxation practice of slow, regular breathing, step-by-step letting go of muscle tension, and pleasant mental imagery can be part of behavioral therapy for anxiety.
It was in this context that I came across the term "default mode" used by neuroscientists to describe brain activity when there are no visual scenes to look at or mental tasks going on. So I wondered how the resting state used in treatment corresponded to the default mode of the brain.
The default mode was described by Marcus E. Raichle when he discovered brain areas that become more active when volunteers are asked to simply lie in the functional MRI (magnetic resonance imagery) scanner, relax, and let their minds wander. Raichle called this activity a "default mode." The same structures decreased activity during a task like identifying objects in a picture.
A functional MRI scanner is a high-tech device that uses magnetic fields to map the brains of volunteers while they look, listen, or perform tasks. It has "made possible some of the greatest breakthroughs in modern neuroscience" while it looks "like a gleaming rocket ship lying on its side," as described by Susan Cain in her perceptive book, Quiet.
When Raichle's brain scans showed separate areas that became active while the mind was at rest, one of these areas was in the front end of the brain, in the prefrontal cortex (the cortex comprises the outer layers of the cerebrum). Another was towards the back, next to the visual cortex. Other studies have included a nearby structure in the midline, the posterior cingulate cortex. In the resting state, these areas show waves of spontaneous activity in sync, like dancers performing identical moves in a 1940's Hollywood musical. The synchronized activity suggested that these brain areas, although in separate locations, are part of a connected network, which Raichle called a default mode network.
What mental state corresponds to the brain's default mode? It's been variously described as the mind wandering, resting, empty, or daydreaming.
The default mode may also occur during mindfulness, when "nonjudgmental awareness of experience in the present moment" takes precedence over rumination about the past or worries about the future. While some types of meditation have been associated with the brain's default mode, other studies, often using different methods, found contradictory results.
More surprising to me were the results of spontaneous eye blinks observed by a research group at Osaka University. Why they recorded their results while their subjects watched videos of Mr. Bean, a favorite British comedian of mine, I don't know, but I assume the participants had some laughs even that high-tech lab environment. Their eye blinks were thought to signal a disengagement of attention. Each blink—lasting about one-third of a second—was associated with a brief activation in the default mode network, although there were some differences in the areas involved compared with those of Raichle.
While some observers would reduce subjective thoughts to be nothing more than neural activity, I disagree. I see your state of mind, influenced by your own intentions and communication with others, as a different domain from the brain activity inferred from the data collected during a brain imaging study, although one can influence the other.
Another complication is that the neuroscience results can be hard to interpret. Parts of the prefrontal cortex, for example, are associated with several roles, including the control of emotional impulses and the re-evaluation of facial expressions. UCLA neuroscientists recently reported increased activity in this area when people are quietly preparing to make social connections.
So if the resting mind corresponds to temporary activity in a "default mode network" found in brain scans, being in the moment might parallel a built-in biological pause for neural refreshment. But how these terms are defined, how these states begin, and how well a relaxed mental state parallels the brain's default mode, are works in progress.