Default Mode Network Activation

These readings examine the role of the default mode network in attention-demanding tasks and associated mind-wandering.

Fox et al. (2005) analyze brain activity in the presence of attention-demanding cognitive tasks. They found that different regions increase in activity (task-positive network) while others decrease (task-negative network) and that this activation/deactivation dichotomy is observed when the brain is at rest, i.e. in the absence of an overt task. Their work therefore supports the model of both correlated and anticorrelated networks associated with the default network. 

Mason et al. (2007), Andrews-Hanna et al. (2010), and Stawarczyk et al. (2011) build on the findings of Fox et al. about the activation of the default mode network during mind-wandering experiences.

In an attempt to understand why and when mind-wandering affects default network activity, Mason et al. (2007) used a thought-sampling method and fMRI imaging to examine which regions of the default network were activated during mind-wandering. Instead of solely comparing SIT production and default network activation between a state of rest versus during a demanding task, they examine such effects during tasks varying in degree of mind-wandering likelihood, depending on whether a task is novel or practiced.  Extending on previous findings, they observe additional cortical areas implicated in the default network, specifically those of the premotor and supplementary motor cortex, which had not been included by Fox et al. (2005). If Mason et al.’s results are indeed correct, in that these regions are active at a resting state, one would expect that Fox et al. would have found them active only in the task-negative network. However, instead Fox et al. notes that the primary sensory and motor cortices are not included in either the task-positive or task-negative network because they are actually activated in both networks, and therefore show no intrinsic network preference. Therefore, these seemingly contradictory conclusions about the activation of the premotor and supplementary motor cortices seem to be a result of the fact that Mason et al. only examined when the brain was “at rest.” 

Using a self-report TUT method in addition to fMRI imaging during tasks varying in the degree of visual attention demanded, Andres-Hanna et al. (2010), attempted to distinguish default network activity resulting from the broadening of external attention compared to that associated with spontaneous cognitive processes (i.e., mind-wandering). As depicted in Figure A, significantly more task-unrelated thoughts were observed by the fMRI during the passive condition (with no event expectations) compared to either the broad or focal attention conditions, in which participants expected either peripheral or foveal events, respectively. From this finding the researchers concluded that default network activity is associated with spontaneous cognition, as those in the passive condition had an increased likelihood to engage in spontaneous cognition.

However, while Andrews-Hanna et al. examine mind-wandering by varying the degree of attention demanded (by manipulating subjects’ task expectations), thus affecting the likelihood of task-unrelated thoughts, the subjects’ conscious experience was not measured during scanning. Such reports were only recorded with a post-study questionnaire (Figure B).  Though these results do confirm the differences in spontaneous cognition observed during the fMRI scans, because they are reported after the scanning, the data could reflect default network activity resulting from factors other than mind-wandering.  Andrews-Hanna et al. therefore would have had more convincing findings had the self-reports been taken during scanning.

Stawarczyk et al. (2011), on the other hand, provide a better way to distinguish and therefore understand these task-unrelated thoughts than Andrews-Hanna (2010) by examining neural correlates of four different types of conscious experiences. They do so by categorizing thoughts by both task-relatedness and stimulus-dependency (See Figure 1) to examine if and how default network activation is associated with task-unrelated and stimulus-independent thought (i.e. mind-wandering). In doing so, they differentiate external distractions from mind-wandering thoughts, a distinction that has been poorly defined and at times completely neglected in the majority of past mind-wandering literature. By making such a distinction, we are able to better understand the default mode network and, more specifically, which of its regions correlate to different conscious experiences.

   

Stawarczyk et al. found that activation associated with task-unrelated and stimulus-independent thought (i.e. mind wandering) are both related to default mode network activity and that the effect can be additive in certain areas while other regions were found to be related to only one dimension. They suggest that, as opposed to being all or nothing, mind-wandering may be a gradual experience that is not necessarily mutually exclusive in relation to other conscious cognitive processes.  Compared to the other articles mentioned, the work by Stawarczyk et al. seems to provide the most valid approach to understanding the default network activity during mind-wandering as it uses thought-probes during fMRI image scans, therefore allowing for a more accurate depiction of the relationship between mind-wandering and associated default mode network activation. 

Everyday effects of mind wandering: where is the silver lining?

This blog post discuses a variety of studies that examine the effects that mind wandering has in our everyday life.  While Baird et al. (2012) examine its potential benefits for future creative problem solving, the majority of studies focus on the negative consequences of mind wandering.  Whether it affects memory (Delaney et al., 2012), reading comprehension (McVay & Kane, 2011), or overall happiness (Killingsworth & Gilbert, 2010), I believe there has to be some reason why we so often mind wander, whether or not it is done consciously. Therefore, while for the most part, these studies focus on negative implications seen in failures of engagement with the present environment, whether we mind wander to plan our future, understand our past, or defend ourselves from the present, there must be some silver lining.

While much research has focused on negative effects of mind wandering, Baird et al. (2012) examine mind wandering’s role in facilitating creative problem solving during breaks or incubation periods, using the Unusual Uses Task (UUT).  All participants solved UUT problems before an incubation periods, after which participants were shown both repeated UTT (repeated-exposure) problems and new UUT (new-exposure) problems.  The incubation period consisted of one of 4 possible conditions: a demanding task, undemanding task, rest condition, or no condition. As predicted, those in the undemanding task condition reported significant improvements in UUT uniqueness scores for the repeated-exposure problems compared to all other conditions (See blue circle marked in Figure 1), while there was no reported difference in uniqueness scores across all conditions on the new-exposure problems.  Because creativity improvement was limited to repeated-exposure problems, suggests that engaging in a task that facilitates mind wandering increases previous creative problem solving but not creativity in general.  It was surprising that those in the rest condition (just sitting quietly during the incubation period) showed no creativity increase for repeated-exposure problems (See red circle marked in Figure 1).  It would be interesting to see what these subjects were mind wandering about because, unlike those in the undemanding task, their mind wandering did not facilitate UUT uniqueness scores. These results may show the importance of undemanding tasks in facilitating the unconscious mind wandering associated with the increase in creative problem solving. Perhaps the control group disassociated completely from the experiment and, instead, engaged in more personally relevant mind wandering compared to the undemanding task condition who were still in an “experiment-mindset,” as they were engaged in an experimental task, causing them to focus on the UUT problems in mind wandering.

Delaney et al. (2012) study the impairments or amnesic effects associated with daydreaming based on a context-change approach.  They predict that increasing distance of thought-content (both temporally and physically) from the present environment will increase forgetting of just-learned information due to a reduced effectiveness of associated retrieval cues. In Experiment 1 (See Figure 1), as predicted, the far-change condition (thought of last time visited parents’ home) showed a significant impairment in remembering words presented immediately prior to daydreaming compared to both the near-change condition (thought of last time at own home) and the control condition (instead of daydreaming, told to quickly read a passage). It is interesting to note there was no significant difference between that remembered by the near-change and control conditions.  Does this insinuate that a similar mind wandering experience was occurring in both conditions, therefore suggesting that we typically mind wander in a near-time/near-distance frame of mind?  This might make sense in relation to the view that we mind wander to personally relevant goals, as it would suggest that we prioritize what is most near.  In addition, findings showed that the longer it had been since participants had visited their parents’ house, the fewer words remembered from List 1 (those presented before daydreaming).  While this finding supports the main hypothesis, I wonder if there is also a possible correlation between feelings associated with one’s home life and the time when they last visited.  If so, perhaps those who hadn’t visited for a relatively long time had stronger and more negative feelings associated with their parents’ home compared to those that visited more recently.  These elicited conflicting emotions could affect the content and strength of associated daydreaming. 

When examining distance (physically), as predicted, the far-change condition (think of an international vacation) reported more memory impairment of List 1 words compared to other conditions. While researchers examined the effect of distance to List 1 words remembered (See Figure 4), they did not test for a time effect. The study extended to include subjects that vacationed anytime within the last 3 years. I think that time since vacation is a crucial factor that should have been measured, especially given the significant time effect found in the previous experiment. 

Overall, while these findings are compelling and arguably plausible, they are meant to explain context-change daydreams, however, the studied “daydreams” are not consistent with what the researchers themselves define as a daydream: “a kind of mind wandering that involves off-task thought”(1036). Because researches directed thinking to daydream, the thoughts generated are actually task-relevant.  They also go on to say that “the more that one’s mental context is changed by daydreaming, the more difficult it becomes to access what one has just experienced” (1040).  However, I am left wondering if there is a difference between one’s mind drifting away from the present to a different context on its own, as opposed to being directed to daydream of a different context.

McVay & Kane (2011) study the mediating role that mind wandering plays in the association between working memory capacity (WMC) and reading comprehension, with individual differences in attention control explaining this relationship.  They take the Control Failures x Concerns View (McVay & Kane, 2010) in which off-task thoughts are automatically generated, based on individuals’ current concerns in addition to environmental cues, from a continuous stream of thought.  Their findings show that low WMC is associated with increased mind wandering and poor reading comprehension while higher WMC is associated with a decreased tendency to mind wander and better reading comprehension. In this executive control-failure view of main wandering, these off-task intrusions have negative effects on performance in demanding tasks, with individuals possessing weaker attention-control abilities (lower WMC) having an increased likelihood of succumbing to these interfering thoughts.  These findings therefore explain, at least in part, WMC’s predictive value for reading comprehension. 

By developing an iPhone application, Killingsworth & Gilbert (2010) created an innovative way to study the association between mind wandering and reported levels of happiness within a real-world context, across a diverse sample of people. Using a probe-caught method through participants’ iPhones, researchers were able to measure subjects during their daily activities and experiences.  In this sample, participants were caught mind wandering much more frequently than laboratory experiments have typically suggested.  This is an important finding as it suggests substantial differences in mind wandering generated in lab versus real-world settings, which could affect the generalizability of lab findings.  In general, subjects from this sample reported being less happy when mind wandering throughout all activities, despite that, for the most part, thoughts were related to pleasant topics. Happiness was strongly related to whether mind wandering occurred in the subject’s previous sample, while it had no significant effect on whether mind wandering occurred in the next sample. From this, Killingsworth & Gilbert conclude that mind wandering seems to be the cause of reported unhappiness. This study therefore demonstrates a possible emotional cost of mind wandering.

This study is noteworthy, mainly due to its use of technology to capture a more real-world picture of mind wandering, which may vary significantly from laboratory studies.  However, I do have reservations about some of the researchers’ conclusions.  Because mind wandering is probe-caught, it is possible that subjects misconstrue their reported unhappiness as a product of mind wandering, though it might actually stem from mind wandering disturbance. The reason I propose this is because participants often reported mind wandering about pleasant thoughts.  Because happiness was measured before questions about mind wandering were asked, it is possible that people attributed their unhappiness to the wrong source (i.e. to mind wandering as opposed to the probe pulling them away from their pleasant thoughts).  Another possibility for these results could be that being probed to notice one is mind wandering is in itself disturbing, leading people feel to unhappy when they become aware they were mind wandering and had no control over it (even though they were actually happy while mind wandering).  In addition, perhaps because mind wandering tends to be seen as a mental weakness or failure, the mere acknowledgement of mind wandering may make people unhappy due to a sense of “being caught in the act.”  While I am only speculating possible effects of this probe-caught method in relation to reported unhappiness, I remain unconvinced that it is the act of mind wandering itself that causes unhappiness.  Perhaps it is not that “a wandering mind is an unhappy mind,”(932) but rather that “a wandering mind caught is an unhappy mind.”