Neural Basis of Mind Wandering and other Spontaneous Thought Processes
When there is no external task to perform, thoughts often flow in a spontaneous and unconstrained manner. These 'undirected' forms of thought are a prevalent aspect of waking mental activity (Christoff, 2012). We have begun to examine the neural basis of such spontaneous thought. An initial fMRI study (Christoff, Ream, & Gabrieli, 2004) found evidence of a considerable contribution from regions in the medial temporal lobe, visual cortex, and the rostrolateral PFC, suggesting that long-term memory, visual imagery, and introspection may form the basis of spontaneous thought. A ubiquitous phenomenon is that of periodically becoming engrossed in such thoughts and losing track of a task at hand (i.e., 'mind wandering'). Yet, the neural underpinnings of mind wandering remain very poorly understood. While prior work suggested that frontal and posterior regions along the medial wall of the cortex (so called “default network” regions) may be the principle substrate underlying mind wandering, our recent work (Christoff, Gordon, Smallwood, Smith, & Schooler, 2009) suggests that default network regions and executive network regions (e.g., dorsolateral prefrontal cortex, rostrolateral prefrontal cortex, and dorsal anterior cingulate cortex) are concurrently engaged during mind wandering—a finding predicted by behavioral theories of off-task thought. This research utilized a combination of objective measures of mind wandering (errors in task performance), subjective self-reports, and brain imaging.
Beyond mind wandering, elucidating the cognitive and neural basis of other spontaneous thought processes has important implications, given the relations to creativity, memory consolidation, decision making, and so on (Christoff, Gordon, & Smith, 2011). Recently, we have argued that dreaming can be considered a form of mind wandering or spontaneous thought: the neural substrate of dreaming is highly similar to the default mode network regions strongly implicated in mind wandering, and subjective content reports from both waking 'daydreams' and night-time dreaming contain many strong similarities (Fox, Nijeboer, Solomonova, Domhoff, and Christoff, 2013). Expanding on the results of (Christoff et al., 2009), which suggested involvement of high-level PFC regions in mind wandering, we have highlighted a number of constructive interactions between metacognition and spontaneous thought processes (Fox and Christoff, 2014).