Similarities and differences in the default mode network across rest, retrieval, and future imagining

Abstract

The default mode network (DMN) has been identified reliably during rest, as well as during the performance of tasks such as episodic retrieval and future imagining. It remains unclear why this network is engaged across these seemingly distinct conditions, though many hypotheses have been proposed to account for these effects. Prior to generating hypotheses explaining common DMN involvement, the degree of commonality in the DMN across these conditions, within individuals, must be statistically determined to test whether or not the DMN is truly a unitary network, equally engaged across rest, retrieval and future imagining. To provide such a test, we used comparable paradigms (self-directed, uninterrupted thought of equal duration) across the three conditions (rest, retrieval, and future imagining) in a within-participant design. We found lower than expected pattern similarity in DMN functional connectivity across the three conditions. Similarity in connectivity accounted for only 40-50% of the total variance. Partial Least Squares (PLS) analyses revealed the medial temporal regions of the DMN were preferentially coupled with one another during episodic retrieval and future imagining, whereas the non-medial temporal regions of the DMN (e.g., medial prefrontal cortex, lateral temporal cortex, and temporal pole) were preferentially coupled during rest. These results suggest that DMN connectivity may be more flexible than previously considered. Our findings are in line with emerging evidence that the DMN is not a static network engaged commonly across distinct cognitive processes, but is instead a dynamic system, topographically changing in relation to ongoing cognitive demands. Hum Brain Mapp 38:1155-1171, 2017. © 2016 Wiley Periodicals, Inc.

Increased fMRI activity correlations in autobiographical memory versus resting states

“…Different cognitive processes also influence both the activation and connectivity of the DMN during resting-state scanning (Bellana, et al, 2017; Benjamin, et al, 2010; Chou, et al, 2017; Demertzi, et al, 2011; Van Calster, et al, 2016; Yan, et al, 2009). Although task-based fMRI has indicated that DMN regions increase in activity for episodic memory and internally driven mentalizing tasks (Buckner, et al, 2008), our findings suggest that relatively long bouts of minimally guided autobiographical retrieval can produce robust changes in the same activity correlation measures used to define networks via resting-state fMRI.…”

“…Bellana, et al (2017) compared autobiographical retrieval versus resting states specifically in the DMN. They found that DMN similarity across autobiographical retrieval and rest accounted for about 42% of the variance of this network, indicating that while there is some stability, a great deal of variability in connectivity exists between these states.…”

Episodic future thinking: mechanisms and functions

“…Related evidence reveals differences in functional connectivity among regions within the default network during episodic remembering and future imagining (48) and indicates that some default network regions (i.e., parahippocampal and retrosplenial cortices) show increased activity during episodic remembering relative to future imagining, likely reflecting enhanced contextual processing for the former compared with the latter (49). …”

Regional Dysregulation and Aberrant Functional Connectivity in ADHD

“…The "default mode network", a regional brain interlocking nexus distinct from other networks, represents a confluence of interacting brain regions, expressing more-or-less synchronically correlated activity, and pathways under activation at times when individuals are unfocused upon the surrounding environment and their brains remain in a state of wakeful rest (Bellana et al, 2016) [14]. It has been found that abnormalities in the intrinsic activity of resting state networks may contribute to the etiology of conduct disorder and poor prognosis of ADHD in combination with conduct disorder (Uytun et al, 2016) [15]; whereas reduced default mode functional connectivity is associated with expressions of conduct disorder (Broulidakis et al, 2016) [16], individuals presenting ADHD present disproportionately high expressions of default mode network activity related to goal-directed tasks accompanied by 'switch-specificity alterations in the right insula region (Sidlauskaite et al, 2016) [17].…”