Where is your mind?

Last week, I had a very embarrassing dialogue with my colleague F. I just came out of the seminar room, chewing a pen (there goes the New Year's resolution). F. said, he was sorry to have missed the seminar and how was it? Well, oohm, I made some vague sounds between so-so and ah-well. Unfortunately, he asked what the seminar was about, and I had to realize that I could neither remember the name of the speaker, nor what he was talking about. Just that he used too much red on his slides.

Anyway, after I've been listening to 'Where is my mind' a whole day (very mind-numbing indeed), I stumbled upon an article in the recent Science issue about the question where wandering minds go

Wandering Minds: The Default Network and Stimulus-Independent Thought
By: Malia F. Mason, Michael I. Norton, John D. Van Horn, Daniel M. Wegner, Scott T. Grafton, C. Neil Macrae

Despite evidence pointing to a ubiquitous tendency of human minds to wander, little is known about the neural operations that support this core component of human cognition. Using both thought sampling and brain imaging, the current investigation demonstrated that mind-wandering is associated with activity in a default network of cortical regions that are active when the brain is "at rest." In addition, individuals' reports of the tendency of their minds to wander were correlated with activity in this network.

In case you don't have a subscription, there is a brief free summary by Greg Miller: Peering Inside the Wandering Mind.

The researchers examined the activity of brain regions with the use of functional magnetic resonance imaging (fMRI). Roughly spoken, magnetic resonance imaging is a way to measure the reaction (resonance) of particles to a magnetic field. If the field is tuned appropriately, the particles resonate and extract energy from the field which can be measured. The strength of the signal depends on the concentration of particles that resonate. More information can be obtained by using pulses and measure the reaction of the particles, such as the relaxation time. You find a more precise introduction here.

So far, so good. Theoretically this can be computed with elementary quantum mechanics. The really challenging task is to get useful 3D-pictures out of the data (essentially a Fourier-transform). By now, this can be done with amazing precision. For some more images, see e.g. this site.

For medical purposes, one mostly uses protons (H), of which there are plenty in water, as well as in proteins. The latter have slightly different resonance properties because they are bound differently. Generally, part of the signal depends on the magnetic properties of the surrounding. Now it turns out that the blood oxygen level influences the magnetic properties since haemoglobin is diamagnetic when oxygenated but paramagnetic when deoxygenated. The signal of blood is therefore slightly different depending on the level of oxygenation. These different signals can be detected using an appropriate magnetic resonance pulse sequence, and is called the blood-oxygen-level dependent (BOLD) contrast.

It is generally believed that the BOLD signal is a measure for neural activity, and this has been used in the study of Mason et al. They examined the active regions of the brains of 19 volunteers which were faced with more or less demanding tasks. The researchers found a particular set of brain regions - the 'default network' - which was more active when tasks were less demanding. If the use of this default network during tasks with low processing demands would indeed reflect mind-wandering, changes in the default networks activity during practiced or novel tasks should be related to the participants score on the 'daydream frequency scale'. The results of the study revealed 'a significant positive relation between the frequency of mind-wandering and the change in BOLD signal observed when participants performed practiced relative to novel' working-memory tasks.

However, the researches also note that day-dreaming likely isn't the only thing that goes on in your brain when tasks 'cease to require conscious supervision' - there might as well be the 'general housekeeping functions' being processed. It also leaves open the question why minds wander:

"Although the thoughts the mind produces when wandering are at times useful, such instances do not prove that the mind wanders because these thoughts are adaptive; on the contrary the mind might simply wander because it can."

One way or the other, if you are sitting in a boring seminar chewing a pen, you're not just inattentive, but you're inspiring your brain's default network to increased activity. If nothing else, it sounds at least more scientific than day-dreaming.

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TAGS: SCIENCE, DAY-DREAMING, MRI, BRAIN