Abstract
The default mode network (DMN) is a set of brain regions that consistently shows higher activity at rest compared to tasks requiring sustained focused attention toward externally presented stimuli. The cognitive processes that the DMN possibly underlies remain a matter of debate. It has alternately been proposed that DMN activity reflects unfocused attention toward external stimuli or the occurrence of internally generated thoughts. The present study aimed at clarifying this issue by investigating the neural correlates of the various kinds of conscious experiences that can occur during task performance. Four classes of conscious experiences (i.e., being fully focused on the task, distractions by irrelevant sensations/perceptions, interfering thoughts related to the appraisal of the task, and mind-wandering) that varied along two dimensions (“task-relatedness” and “stimulus-dependency”) were sampled using thought-probes while the participants performed a go/no-go task. Analyses performed on the intervals preceding each probe according to the reported subjective experience revealed that both dimensions are relevant to explain activity in several regions of the DMN, namely the medial prefrontal cortex, posterior cingulate cortex/precuneus, and posterior inferior parietal lobe. Notably, an additive effect of the two dimensions was demonstrated for midline DMN regions. On the other hand, lateral temporal regions (also part of the DMN) were specifically related to stimulus-independent reports. These results suggest that midline DMN regions underlie cognitive processes that are active during both internal thoughts and external unfocused attention. They also strengthen the view that the DMN can be fractionated into different subcomponents and reveal the necessity to consider both the stimulus-dependent and the task-related dimensions of conscious experiences when studying the possible functional roles of the DMN.
Highlights
During the last decade, the default mode network (DMN) of the brain—a network of brain regions that includes the medial prefrontal cortex (MPFC), the posterior cingulate cortex (PCC)/ restrosplenial cortex (Rsp), the medial and lateral temporal lobes, and the posterior inferior parietal lobes—has become the object of intensive focus and research in neuroscience [1,2]
A second analysis of variance (ANOVA) was conducted on the variability of response times (RTs): we observed a main effect of task-relatedness [F(1,21) = 4.39; p,0.05; partial g2 = 0.17], no main effect of stimulus-dependency [F(1,21) = 1.90; p = 0.18; partial g2 = 0.08], and a significant interaction [F(1,21) = 8.71; p,0.01; partial g2 = 0.29], indicating that reports of being completely focused on the task were preceded by more stable RTs than the three other classes of reports
The present study aimed at clarifying this issue by investigating the neural correlates of the various kinds of conscious experiences that can occur while participants perform a task requiring sustained focused attention and the cognitive processing of external stimuli
Summary
The default mode network (DMN) of the brain—a network of brain regions that includes the medial prefrontal cortex (MPFC), the posterior cingulate cortex (PCC)/ restrosplenial cortex (Rsp), the medial and lateral temporal lobes, and the posterior inferior parietal lobes (pIPL)—has become the object of intensive focus and research in neuroscience [1,2]. The dorsal anterior cingulate and lateral prefrontal cortex were engaged during off-task thoughts, suggesting a processing overlap between mind-wandering and central executive resources These neuroimaging findings suggest that mindwandering is associated with the recruitment of both DMN and executive network regions, it should be noted that participants were asked to report whether they were totally focused on the proposed task (on-task reports) or were distracted by taskunrelated thoughts (off-task reports). Region of interest (ROI) analyses were performed in order to investigate whether distinct subregions of the MPFC that have been identified in previous studies (see above) are differentially sensitive to task-relatedness and stimulus-dependency Results of these analyses demonstrate the relevance of our finer-grained conceptualization of ongoing conscious experiences for explaining variations in DMN activity. Both the ‘‘task-relatedness’’ and ‘‘stimulus-dependency’’ dimensions were related to activity in several regions of the DMN, suggesting that these regions underlie cognitive processes that are active during both internal thoughts and unfocused external attention
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