Bipartite Functional Fractionation within the Default Network Supports Disparate Forms of Internally Oriented Cognition

Abstract

Our understanding about the functionality of the brain’s default network (DN) has significantly evolved over the past decade. Whereas traditional views define this network based on its suspension/disengagement during task-oriented behavior, contemporary accounts have characterized various situations wherein the DN actively contributes to task performance. However, it is unclear how different task-contexts drive componential regions of the DN to coalesce into a unitary network and fractionate into different subnetworks. Here we report a compendium of evidence that provides answers to these questions. Across multiple analyses, we found a striking dyadic structure within the DN in terms of the profiles of task-triggered fMRI response and effective connectivity, significantly extending beyond previous inferences based on meta-analysis and resting-state activities. In this dichotomy, one subset of DN regions prefers mental activities “interfacing with” perceptible events, while the other subset prefers activities “detached from” perceptible events. While both show a common “aversion” to sensory-motoric activities, their differential preferences manifest a subdivision that sheds light upon the taxonomy of the brain’s memory systems. This dichotomy is consistent with proposals of a macroscale gradational structure spanning across the cerebrum. This gradient increases its representational complexity, from primitive sensory-motoric processing, through lexical-semantic representations, to elaborated self-generated thoughts.

Default Mode Network spatial configuration varies across task domains

“…Their spatial resemblance seems to indicate that, despite being orthogonal, these two components may be related to a similar phenomenon. In fact, we note that they both resemble the SemN (Chiou et al, 2020;Evans et al, 2020;Noonan et al, 2013). Furthermore, they remind the transitional module serving an integrative function with the frontoparietal task-positive system observed by Fornito and colleagues (2012), as well as with the Overlapping Community 6 found by Najafi and colleagues (2016).…”

“…Since those observations, many further functions were shown to be associated to this network. Other than self-referential and emotional processes (Buckner and Carroll, 2007; D’Argembeau et al, 2010; Denny et al, 2012; Engen et al, 2017; Fingelkurts et al, 2020; Fossati et al, 2003; Knyazev et al, 2020; Molnar-Szakacs and Uddin, 2013; Northoff et al, 2006; Northoff and Bermpohl, 2004; Ochsner et al, 2005, 2004; Satpute and Lindquist, 2019; Uddin et al, 2007), the DMN turned out to be related to memory and mental time-travel (Addis et al, 2007; Cabeza et al, 1997; Foster et al, 2012; Kim, 2016; Murphy et al, 2018; Rugg and Vilberg, 2013; Schacter et al, 2008, 2007; Spreng et al, 2015; Svoboda et al, 2006; Yang et al, 2013), mental simulation and scene construction (Gerlach et al, 2011; Hassabis et al, 2007; Hassabis and Maguire, 2007; Spreng and Grady, 2010), theory of mind (ToM) and social cognition (Amft et al, 2015; Mar, 2011; Mars et al, 2012; Mwilambwe-Tshilobo and Spreng, 2021; Rilling et al, 2004; Ruby and Decety, 2004; Saxe and Kanwisher, 2003; Saxe and Powell, 2006; Spreng and Andrews-Hanna, 2015), moral judgment (Bzdok et al, 2012; Greene et al, 2001; Harrison et al, 2008; Pujol et al, 2008), semantic processing (Binder et al, 1999, 2009; Chiou et al, 2020; Evans et al, 2020; Lanzoni et al, 2020), and reward mechanisms (Lopez-Persem et al, 2020; Martins et al, 2021; Xue et al, 2009). However, most of these psychological functions can still be somewhat associated with the resting state (Wen et al, 2020).…”

The Functional Convergence and Heterogeneity of Social, Episodic, and Self-Referential Thought in the Default Mode Network

“…Given these findings, future studies should consider further the relation between social cognition and the semantic control network, including the IFG. One possibility is that the IFG acts as a gateway to the DMN, via the semantic control network, when semantic retrieval is constrained by external stimuli ( Chiou et al. 2019 ).…”

“…2009 ; Humphreys and Lambon Ralph 2017 ), episodic ( Ranganath and Ritchey 2012 ; Rugg and Vilberg 2013 ), and self-referential ( Kelley et al. 2002 ; Chiou et al. 2019 ) cognition.…”

A tale of two gradients: Differences between the left and right hemispheres predict semantic cognition and visual reasoning

“…Just as we found a control network that was closer to the heteromodal end of the principal gradient in LH, DMN-B (the adjacent network), showed the same pattern. DMN-B includes regions such as lateral ATL, angular gyrus, inferior frontal gyrus and dorsomedial prefrontal cortex that are associated with semantic processing in the left hemisphere (Jackson, 2021; Jefferies, 2013; Lambon Ralph et al, 2017; Noonan et al, 2013; Rice et al, 2015), and this DMN variant has repeatedly shown functional dissociations with core DMN regions such as posterior cingulate cortex and more ventromedial prefrontal regions (Chiou et al, 2020; Zhang et al, 2020; referred to here as DMN-A). DMN-B is associated with lateralised cognitive processes, like language and semantics, as well as social cognition (Andrews-Hanna et al, 2014).…”