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.”

Executive-function vs. Executive-failure theories of mind wandering

     This blog focuses on the discourse between Smallwood & Schooler (2006), McVay & Kane (2010), and Smallwood (2010), in which two compelling theories of mind wandering are juxtaposed in order to address the advantages and potential flaws of each.

Smallwood and Schooler (2006) present an executive-function theory, in which they suggest that mind wandering results from the automatic activation of control processes, causing attention to shift away from the task-relevant external environment, and instead towards personally-relevant goals.  Mind wandering, in this viewpoint, is caused by the activation of unresolved goals (also called current concerns).  Tasks that therefore rely on control processing should cause a suppression of mind wandering.  When the mind does wander, one’s ability to coordinate task-relevant information into awareness will be impaired as the necessary control processes are directed elsewhere.  In other words, consciousness becomes decoupled with the external task environment and instead is coupled with internalized processes.
       In direct response to the theory suggested by Smallwood & Schooler (2006), McVay & Kane (2010) instead propose an executive-control failure theory of mind wandering, in which, unlike the executive-function theory, mind wandering does not rely on the same executive control resources allocated towards the present task. Instead they argue that mind wandering is the result of a failure of executive control over task-irrelevant thoughts. While both of these theories suggest that the content of mind wandering thoughts consists of present, urgent, and task-irrelevant goals, in the executive-failure theory, these thoughts occur only when the executive control system fails to defend against them.  This difference between the two theories is critical to understand how each has very different implications in relation to the processes of mind wandering.

       It does seem that the executive-failure theory is better at explaining evidence of individual differences as well as findings found in studies involving alcohol intake as well as disorders like ADHD.  ADHD is associated with deficits on executive-function tasks.  Those diagnosed with ADHD show increased reports of TUTs compared to healthy controls.  It is postulated that if the executive-function theory were true then the deficits in executive functions would cause a decrease in TUT propensity compared to controls, given that the same resources for executive-function tasks (which show deficits) would be needed for mind wandering.  Therefore, this data would seem to directly contradict the executive-function theory.  However, is it possible that those with ADHD show deficits on executive-function tasks because they mind wander more?  In other words, compared to normal subjects do individuals with ADHD just more readily devote their resources to mind wandering?  If so, these findings would not only fail to contradict the executive-function theory, but would also help explain why these deficits on executive-function tasks occur for those with ADHD.  Depending on the proportion of resources devoted to mind wandering, this deficit could be the result of a higher propensity of those with ADHD to attend more strongly to mind wandering than controls not because of a significant lack of executive resources but rather the way in which they prioritize where to allocate them.  

        McVay & Kane (2010) encounter a slight problem while trying to explain results of studies looking into aging, as older adults have been found to report less mind wandering than younger adults, despite the fact that older adults have more executive control deficits than younger adults.  In order to account for this discrepancy, the researchers introduce a second factor—the current concerns theory—in which they argue that older adults have fewer concerns during testing and, therefore, report less mind wandering than younger adults.  This seems like an unsupported conclusion to explain these findings, and the results actually support the executive-function theory quite well, which causes me to question this explanation further.

       Neuroimaging has offered some important insight into the functionality of mind wandering, implicating brain regions mainly associated with executive control.  fMRI studies have shown that the default network regions are significantly more activated prior to reports of mind wandering compared to activation prior to reports of being “on-task” (Christoff et. al, 2009). This finding that the default network regions are employed more during mind wandering episodes offers support of the executive-function theory through a measure based on more than just self-report. In addition Christoff et al. compared activation of these regions during mind wandering with and without meta-awareness (see Figure 4).

Figure 4

These images show that there is more activity in these default regions when subjects are unaware of mind wandering, compared to during states of meta-awareness.  This raises problems in light of the executive-failure theory.  McVay & Kane try to reconcile why there might be more activation during mind wandering without meta-awareness by suggesting that such activation may reflect one’s effort to refocus on the present task and that conscious awareness is not needed for this refocusing to happen. Not only does this seem unlikely, but the researchers also ultimately do not offer any reasoning as to why this might be the case.  McVay & Kane’s lack of explanation, in addition to the activation visibly seen in the fMRI images, cause me to lean further in favor of the executive-function theory of mind wandering.  Additionally, I think that the increase in eye movement during meta-awareness (self-caught) compared to mind wandering without meta-awareness (probe-caught), in eye-tracking studies reflects the subjects’ attempts to refocus on the task at hand. If so, then this refocusing during a state of meta-awareness would refute McVay & Kane’s claim. 
     In light of mind wandering research findings since 2006, Smallwood (2010) explains and re-articulates the claims made by Smallwood & Schooler (2006) that McVay & Kane (2010) argue against.  Smallwood assumes the position that, because mind wandering is a conscious, reportable state, implies that it is globally available to the system and therefore does demand resources.  While the executive-failure theory explains mind wandering during difficult tasks, unlike this global availability hypothesis, it fails to do so across all contexts.  More specifically, while the executive-failure theory is promising in relation to keeping unwanted thoughts out of the mind, it is not as firmly supported when explaining mind wandering in relatively easy, nondemanding tasks where thoughts are most likely not “unwanted,” as such thoughts may actually be advantageous for planning and creativity.  While the cognitive failure theory may be applicable during demanding tasks, in which mind wandering does result from a failure in proactive maintenance of task-relevant environment, Smallwood (2010) argues that this would occur within the context of the executive-function theory because mind wandering itself is a conscious process.

      Based on these articles and the evidence provided, the executive-function theory seems to support the majority of these lapses found in mind wandering research, though further research is needed to address the discrepancies which have been found (e.g. the ADHD studies previously mentioned). Within the executive-function theory approach, it is important to note the paradox of mind wandering itself, as decoupling from one’s present environment is detrimental to current task goals, while the coupling with internalized goals that results may provide important cognitive benefits in regards to planning and creativity.

The consequences of our wandering minds

           
          Our minds wander-it's an unavoidable truth.  Studying how and why we enter these periods of unintended thought is therefore crucial to understand how our minds function.  Giambra (1995) found that the propensity of task-unrelated images and thoughts (TUITs) is a reliable measure over a variety of vigilance tasks. In these studies he used a probe-TUIT method to measure TUIT propensity, which was found to be both sensitive to conditions of a concurrent task and also able to maintain individual differences over different tasks and task conditions, as well as over short and long time-intervals. 

Consistent with past vigilance research, Giambra found that target response time was faster for the condition with a larger percentage of target stimuli. However, the reported interaction between response time and event rate was atypical, with response time progressively increasing as event rate increased.  This finding contradicts past literature, in which it has been found that an event rate of 15/min has a faster response time than that of 30/min.  In order to account for both findings, Giambra suggests that the relationship between target response time and event rate may be u-shaped (see graph below for a rough depiction). This explanation definitely raises some flags as this u-shaped curve is unsupported by past research and seems to be a forced way to make both results fit together. However, there was also no association found between response time and P-TUIT frequency, so it remains unclear what caused these unique results.

           The work of Reichle, Reineberg, & Schooler (2010) examines readers’ eye-movements in normal reading, mindless reading, and during meta-awareness, in order to assess the degree that cognition influences eye movements during normal reading. Just as Giambra used the probe- method to measure TUIT frequency, here a probe-caught mind wandering method is used to measure eye movements when participants are in the middle of mind-wandering (i.e. they have not entered meta-awareness, which occurs when mind wandering is self-caught).  Results indicate that longer text fixations are indicative of mindless reading and that the mind wanders for a considerably long time before self-caught (2-4 minutes), during which eye movements become increasingly decoupled from text processing.  This study provides evidence for the use of tracking eye movements as on-line indicators of mind wandering.  However, it is important to note the small sample size, 75% of which was female (3 females and 1 male).

            This being said, it is crucial to note the significant implications gender effect had in many of the mentioned studies. This is specifically noteworthy in the work of Antrobus, Singer, & Greenberg (1966) when testing the interaction between task significance (i.e. payoff) on responding to stimuli and amount of TUITs generated.  Researchers hypothesized that increasing the payoff of signal detection would cause a decrease in the reported occurrence of TUITs. With a starting value of $3.00, participants in three experimental conditions were told there would be a penalty for detection error (1/5, 2/5, or 4/5 cents per error). When analyzing the findings across all subjects (Figure 1), the expected increase in penalty associated with a decrease in TUITs was not as strong as predicted. However, this relationship drastically changed when gender was accounted for (Figure 2). 

1]

[2]

             By comparing this difference between male and female subjects, researchers concluded that the predicted payoff effect was exclusively and strongly characteristic of male subjects.  They suggested that this difference might indicate that the reward of mastering the task and performing well for these “high-achieving college girls” was more important than the monetary payoff. Studies, such as that of   Vallerand & Bissonnette (1992), have found that compared to males, females tend to be more intrinsically motivated, less externally regulated, and display higher levels of behavioral persistence. Even further, this is not specific to “high-achieving college girls,” as this gender difference has been found as early as kindergarten.  These findings therefore support the proposed explanation provided by Antrobus et al. when trying to account for the reported gender effect. However, in order to measure this more accurately, researchers should have used a self-report measure to assess the importance each participant placed on monetary value and task performance.

           Further, when analyzing the probability of missing a signal (P(Miss)) as a function of penalty, increasing penalty was associated with a decrease in TUITs (P(Report)), which resulted in the predicted decrease in P(Miss) for the male subjects. A point that the authors should have addressed was the lack of gender effect in the interaction of P(Miss) and penalty (see Figure 3).  Given the significant gender effect in the interaction of P(Report) and penalty (Figure 2), would mean that, for these female subjects, P(Miss) was not inversely related to P(Report).  This suggests that the same cognitive resources were actually not being used for both TUIT and signal detection for these females. Whether this is a result of the undemanding task or the weak relation between payoff and detection accuracy, it highlights the impact that gender may play in mind wandering research.

In a study by Teasdale et al. (1995) task practice reduced the extent that task performance interfered with TUIT frequency.  Supporting past research that TUIT production and task performance both demand central resources of control and coordination, this finding suggests that practice reduces the resources demanded for the task, thus increasing resource availability for TUIT production. However, it is important to note that only female subjects were tested in these studies. After observing the gender effect in the study by Antrobus et al., I would refrain from generalizing Teasdale’s findings to male subjects.  This previously observed gender effect suggests the possibility that task practice might only mediate the central resource demands of females, as a result of their higher levels of intrinsic motivation, which may increase their likelihood to learn from practice and perform well on a task, compared to males.

            So far in this post, research has focused on the negative effects of TUITs, however, a subsequent experiment by Antrobus et al. addresses the importance of cognitive spontaneous thought, especially when incompatible with one’s existing conception of his/her projected environment.  A significant effect of pretask condition on TUIT frequency during a subsequent task was found, such that subjects exposed to a radio broadcast announcing that the US had declared war reported a significant increase in TUITs compared to the control group.

          Based on these findings, when conducting his study, Giambra acknowledged that prior events could influence subsequent TUIT frequency, and therefore manipulated whether participants played an uninteresting video game (control condition) or solved a mental puzzle (experimental condition), with the puzzle expected to produce more TUITs, as subjects would still be thinking about it during the relatively boring subsequent vigilance task. However, I do not believe that Giambra’s pretask conditions were comparable to those of Antrobus et al. While Giambra’s mental puzzle condition might engage and frustrate subjects, I would expect emotions evoked from the broadcast in Antrobus’ experiment to be much stronger with more of a lasting impression, as it presented life-changing news with serious implications directly affecting the subjects.  In addition, to me, the “condition group” of the video game sounded just as frustrating as the puzzle (if not more so) as it provided no instructions, made no logical sense, and therefore could have made subjects upset and frustrated after realizing they lacked any control in the outcome, which could have equally carried over as much distraction as the thoughts from the puzzle pretask condition.  The fact that thoughts reported by the experimental condition in the study by Antrobus et al. were related to the war and its potential effects on the subjects' lives, suggests an increase in payoff for this planful spontaneous thinking.  This is an interesting extension from Antrobus’ previous experiment (mentioned earlier) which had involved a monetary penalty for wrong detection. While in the previous experiment the payoff was within the task itself, in this later study the payoff actually came from the production of TUITs related to information provided in the broadcast.  

[1] http://www.amsciepub.com/doi/pdf/10.2466/pms.1966.23.2.399

[2] http://www.amsciepub.com/doi/pdf/10.2466/pms.1966.23.2.399