Elsevier

Brain Research

Volume 1428, 5 January 2012, Pages 51-59
Brain Research

Research Report
Undirected thought: Neural determinants and correlates

https://doi.org/10.1016/j.brainres.2011.09.060Get rights and content

Abstract

While goal-directed thinking has received the lion's share of neuroscientific attention, its counterpart—the undirected thought flow that comes to mind unbidden and without effort—has remained largely on the sidelines of scientific research. Such undirected thought, however, forms a large part of our mental experience. The last decade of neuroscientific investigations marked a resurgence of interest and work into the neural basis of undirected thought. This article reviews the current status of the field and examines the research on the three most frequently discussed categories of undirected thought: spontaneous thought, stimulus-independent thought, and mind wandering. The terminology and paradigms for investigating undirected thought are still being developed, while research is gradually moving beyond strictly task- and rest-based paradigms and towards incorporating introspective first-person reports in order to better understand this phenomenon. It is impossible to say at this point that undirected thinking is preferentially linked to any one particular brain system. Although its connection to the default network has been disproportionately emphasized in the literature, other brain networks such as the executive system and the temporal lobe memory network appear to be equally involved. In addition to reviewing the literature, this article also presents novel findings regarding the functional connectivity between large-scale brain networks during mind wandering. These findings reveal the presence of positive functional connectivity between regions of the default and executive networks and negative functional connectivity between the default network and primary sensory cortices. Thus, the default and executive networks can closely cooperate in supporting undirected thought processes, and seem to do so at times when the primary sensory cortices are not busy with the processing of perceptual information from the external environment.

This article is part of a Special Issue entitled The Cognitive Neuroscience of Thought.

Introduction

Most people view thinking as a goal-directed phenomenon, or a mental process deliberately employed towards solving a problem or making progress on a task. In contrast, another much less dominant view has emphasized thinking's undirected, spontaneous nature—from William James' discussion of the thought's tendency to drift (James, 1980), to research on daydreaming during the 1960s (Antrobus et al., 1966, Singer and Schonbar, 1961), to more recent research on spontaneous thought and mind wandering (Christoff et al., 2009a, Christoff et al., 2004, Klinger and Cox, 1987, Smallwood and Schooler, 2006, Teasdale et al., 1995).

The last decade of neuroscientific investigations marked a resurgence of interest and work into the neural basis of undirected thought. The research is still in its infancy and there is no clear agreement about the most appropriate terminology to use. For example, is all daydreaming undirected? Is mind wandering the same as daydreaming? These questions remain unanswered. It is clear, however, that undirected thought forms a large part of our mental experience. Ninety-six percent of American adults report some kind of daydreaming each day (Singer and McCraven, 1961) and at least 30% of thoughts that people experience in their daily lives can be classified as mind wandering, as defined by their lack of relation to the current task (Kane et al., 2007, Killingsworth and Gilbert, 2011, Klinger and Cox, 1987). Furthermore, as many as 50% of thoughts can be classified as daydreaming, defined as a nonworking thought that was either spontaneous or fanciful (Klinger, 2009). Given this striking prevalence of undirected thought in our mental experience, it is clear that understanding its neuroscientific underpinnings is a necessary step towards improving our overall understanding of human thought.

The terms “spontaneous thought” (Christoff et al., 2011b, Christoff et al., 2004) “stimulus-independent thought” (Gilbert et al., 2007, Mason et al., 2007a, Mason et al., 2007b, McGuire et al., 1996), and “mind wandering” (Christoff et al., 2009a, Schooler et al., 2011, Smallwood and Schooler, 2006) have been used most frequently during the last decade of neuroscientific investigations. The term “task-unrelated thought” has also been used in the literature, largely overlapping with the way “mind wandering” has been operationally defined. All these terms are sometimes used interchangeably although they are by no means the same thing. Furthermore, the definition of each of these terms is often different across different researchers and sometimes even across different publications by the same researchers.

This terminological fluidity is understandable; the neuroscience of undirected thought is still in its infancy. To some extent such fluidity is useful in that it allows researchers to continue to improve their definitions as they learn more about the relevant phenomena. Partly because of this terminological uncertainty and partly because the experimental paradigms for its study are still developing, it is impossible to say at this point that undirected thinking is preferentially linked to any particular brain systems. A connection between undirected thought and the default network has been empirically demonstrated on a number of occasions (e.g., Christoff et al., 2009a, Mason et al., 2007b). However, other brain networks such as the executive system and the temporal lobe memory network appear to be equally involved (Christoff et al., 2009a, Christoff et al., 2004, Stark and Squire, 2001).

This article reviews the three most frequently investigated forms of thought—spontaneous thought, stimulus-independent thought, and mind wandering—that are considered to be largely undirected. Almost all of neuroscientific investigations so far have used rest as an experimental paradigm to study undirected thought. During rest, subjects are simply instructed to do nothing. No experimental task is given to them, and they are typically presented with a blank screen in front of them while they are lying in the scanner. This minimizes the external perceptual and cognitive demands on subjects, and as behavioral research has consistently shown (Filler and Giambra, 1973, Giambra and Grodsky, 1989), conditions of low external demands result in high rate of undirected thoughts, such as daydreaming, mind wandering, or stimulus independent thought. However, the existence of such undirected thoughts during rest is only indirectly inferred. By contrast, using experience sampling—a procedure during which subjects are asked to report on the quality of their thought experience in an online fashion, as these thoughts occur in the scanner—offers a more direct way of investigating undirected thought processes, but has only begun to be used very recently (Christoff et al., 2009a). As the field progresses, both experimental paradigms and terminology will undoubtedly become more sophisticated.

The term “undirected thought” is used here in the sense of “not deliberately directed” by the thinker, and in contrast to the usual way in which goal-directed thought is conceptualized. While undirected thought is not deliberately directed towards a particular goal or outcome, its direction may be implicitly biased or influenced by the thinker's current concerns or emotional states. In that sense, undirected thought is not necessarily completely undirected—for example, spontaneous thought can be biased by making personality traits self-relevant (Smallwood et al., 2011, Smallwood et al., 2009) or by priming an individual's “to do list” (Stawarczyk et al., 2011). However, the crucial feature of undirected thought is that it proceeds without the conscious, deliberate effort for channeling its course in particular direction on the part of the thinking person.

In addition to reviewing the current status of undirected thought research, this article also presents novel findings regarding the functional interactions between the default and executive network, on the one hand, and the primary sensory cortices, on the other hand. The functional interrelation between these large-scale brain networks during undirected thought is one of the most intriguing but as of yet largely unexamined research directions.

Section snippets

Spontaneous thought

Spontaneous thought can be defined as the unintended, nonworking, noninstrumental mental content that comes to mind unbidden and effortlessly (Klinger, 2009). What distinguishes spontaneous thoughts from deliberate thoughts is the way in which they occurred and the extent to which the thinker deliberately directs them (Klinger, 2009). Conceptually, spontaneous thought differs from mind wandering and stimulus-independent thought. For example, if mind wandering is defined as thinking that's

Stimulus-independent thought

Within the context of cognitive neuroscience, the term stimulus-independent thought is sometimes used interchangeably with the term mind wandering (e.g., Mason et al., 2007a, Mason et al., 2007b). However, the two are conceptually different. In general, stimulus-independent thought is easier to define than mind wandering. By definition, stimulus-independent thought is decoupled from current sensory information (Antrobus, 1968, Teasdale et al., 1993). This could occur in the form of mind

Mind wandering

Although there have been relatively few studies of mind wandering (Christoff et al., 2009a, Mason et al., 2007b, McKiernan et al., 2006), our neuroscientific knowledge of this phenomenon is greater than for either spontaneous thought or stimulus-independent thought due to these studies' use of individual differences analysis and experience sampling approach combined with fMRI measures.

Within the neuroimaging literature, so far mind wandering has most often been defined as thinking that is

Functional connectivity between large-scale brain networks during undirected thought

To examine the functional relationship between default and executive network regions during mind wandering, we performed functional connectivity analysis on the dataset from Christoff et al. (2009a). Time series were extracted from three main ROIs activated during mind wandering, as identified in the off-task versus on-task comparison (Fig. 1)—the dACC (part of the executive network), and the vACC and PCC/precuneus (both part of the default network). The ROIs were first defined at the group

Conclusions and future directions

The cognitive neuroscience of thought during the last decade has seen a newly emerged emphasis on undirected thought processes. This emphasis originally came from the ubiquitously observed neural recruitment during rest and was expanded through more recent direct empirical investigation of mind wandering. These investigations have revealed that contrary to most people's intuitive beliefs, the mind may be most active when it is freely wandering outside the confines of particular tasks or goals.

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