|I think, therefore I am (unhappy)
Dept. of Epileptology, Univ. of Bonn, Germany
When not performing a task, we are usually engaged in a variety of thoughts, for instance about current problems, opportunities, our self-image, our relationships, about past experiences and about plans for the future. Such mind wandering was found to occupy almost half of our time spent awake (Killingsworth and Gilbert, 2010). Mind wandering may have had the evolutionary advantage of better adapation to changing environmental and social circumstances, because it allows the mental contemplation of issues remote from the here and now (Schooler et al., 2011).
But mind wandering also has substantional downsides. Even when we are performing a task, our minds tend to wander. This divagation into situation- independent thoughts usually goes unnoticed and it leads to impaired task performance (e.g. Christoff et al., 2009; Schooler et al., 2011). Depending on the task, this actually may be dangerous, for instance when driving a vehicle (He et al., 2011). Furthermore, mind wandering is related to negative emotions (e.g. Smallwood et al., 2009). A recent study has demonstrated that people are less happy when their minds are wandering to neutral topics than when their minds are focused on their current activity (Killingsworth and Gilbert, 2010). And even when thinking about pleasant topics, they are not happier than when they focus on the task at hand (Killingsworth and Gilbert, 2010).
Knowledge about the negative effects of mind wandering has been available for a long time in various religious traditions, in particular in Buddhism. The practice of mindfulness meditation aims at reducing the prevalance of uncontrolled thought chains by increasing meta-awareness of ongoing mental activities. The finding that mind wandering related brain activations (see below) are diminished in case of meta-awareness (Christoff et al., 2009) provides neuroscientific validation for this strategy. Today, elements of mindfulness meditation have been implemented in several therapeutic systems, such as mindfulness-based stress reduction (Ludwig and Kabat-Zinn, 2008) and mindfulness-based cognitive therapy (Segal et al., 2002). These techniques are applied, for instance, for the treatment of attention deficit disorder, psychosomatic disorders and depression.
But is there neuroscientific evidence that mindfulness training indeed reduces neural activations associated with mind wandering? Recent fMRI studies support this assumption. First of all, mind wandering was found to be associated with activations in so-called default mode brain areas (Christoff et al., 2009; Hasenkamp et al., 2012; Stawarczyk et al., 2011). These brain areas were demonstrated to exhibit increased activity during task-free periods and decreased activity during goal-oriented behaviour as measured by functional brain imaging (Raichle et al., 2001).
A recent study investigated activations in default mode areas in subjects with no, moderate and high meditation experience during daydreaming and mindfulness meditation (Ott et al., 2010). The authors observed an inhibition of default mode network activity during mindfulness meditation compared to the daydreaming condition. Moreover, the inhibition of anterior default mode areas, which have been argued to be associated with self-related and social cognition (Northoff et al., 2006), was more persistent in subjects with high compared to no meditation experience.
Another study addressed the neural correlates of conceptual processing in regular Zen (a particular kind of mindfulness meditation) practitioners compared to matched control subjects. Participants were required to decide whether sparsely presented visual stimuli were real English words or strings of letters with plausible readings but no semantic content (Pagnoni et al., 2008). The words, compared to the non-words, are likely to trigger a cascade of semantic associations. Moreover, participants were instructed to attend to their breathing throughout the scan and to promptly re-focus attention to their breathing after responding to the stimuli. The authors found that Zen practitioners, compared to controls, displayed a reduced duration of semantic processing effects in default mode brain areas suggesting greater ability to disengage from mind wandering.
Finally, a recent study investigated the neural substrates of mindfulness in subjects who had undergone a mindfulness-based stress reduction intervention and had practiced mindfulness daily for a minimum of 4 years (Ives-Deliperi et al., 2011). Activations during mindfulness meditation were compared to a number-generation control task. The authors observed mindfulness-related signal decreases mainly in cortical midline structures, which are known to be related to interoception and self-related mental processes (Northoff et al., 2006) and which are, again, part of the default mode network.
To conclude, recent fMRI studies revealed reduced neural activations within default mode brain areas during mindfulness practice. These data represent preliminary neuroscientific support for the idea that mindfulness training is an efficient method to reduce neural processes associated with mind wandering and task-independent thoughts. However, additional studies are needed to corroborate these initial findings. Furthermore, it is still unclear whether mindfulness-related alterations of neural activations are directly linked to modifications of behaviour and whether mindfulness training can induce persistent changes in the default mode network.