Wandering Minds: The Default Network and Stimulus-Independent Thought
19 Jan 2007-Science (American Association for the Advancement of Science)-Vol. 315, Iss: 5810, pp 393-395
TL;DR: It was demonstrated that mind-wandering is associated with activity in a default network of cortical regions that are active when the brain is “at rest” and individuals' reports of the tendency of their minds to wander were correlated with activity on this network.
Abstract: Despite evidence pointing to a ubiquitous tendency of human minds to wander, little is known about the neural operations that support this core component of human cognition. Using both thought sampling and brain imaging, the current investigation demonstrated that mind-wandering is associated with activity in a default network of cortical regions that are active when the brain is "at rest." In addition, individuals' reports of the tendency of their minds to wander were correlated with activity in this network.
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TL;DR: Past observations are synthesized to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment, and for understanding mental disorders including autism, schizophrenia, and Alzheimer's disease.
Abstract: Thirty years of brain imaging research has converged to define the brain’s default network—a novel and only recently appreciated brain system that participates in internal modes of cognition Here we synthesize past observations to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment Analysis of connectional anatomy in the monkey supports the presence of an interconnected brain system Providing insight into function, the default network is active when individuals are engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others Probing the functional anatomy of the network in detail reveals that it is best understood as multiple interacting subsystems The medial temporal lobe subsystem provides information from prior experiences in the form of memories and associations that are the building blocks of mental simulation The medial prefrontal subsystem facilitates the flexible use of this information during the construction of self-relevant mental simulations These two subsystems converge on important nodes of integration including the posterior cingulate cortex The implications of these functional and anatomical observations are discussed in relation to possible adaptive roles of the default network for using past experiences to plan for the future, navigate social interactions, and maximize the utility of moments when we are not otherwise engaged by the external world We conclude by discussing the relevance of the default network for understanding mental disorders including autism, schizophrenia, and Alzheimer’s disease
8,448 citations
Cites background from "Wandering Minds: The Default Networ..."
...The default network also includes connections with the HF and overlaps with regions active during episodic remembering (e.g., Greicius et al. 2004, Buckner et al. 2005, Vincent et al. 2006)....
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...Mason et al. (2007) recently extended these approaches to study individual differences....
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...The sentinel hypothesis is consistent with certain properties of the default network as well as attentional deficits following bilateral posterior lesions....
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TL;DR: New findings suggest a fundamental role for the AIC (and the von Economo neurons it contains) in awareness, and thus it needs to be considered as a potential neural correlate of consciousness.
Abstract: The anterior insular cortex (AIC) is implicated in a wide range of conditions and behaviours, from bowel distension and orgasm, to cigarette craving and maternal love, to decision making and sudden insight. Its function in the re-representation of interoception offers one possible basis for its involvement in all subjective feelings. New findings suggest a fundamental role for the AIC (and the von Economo neurons it contains) in awareness, and thus it needs to be considered as a potential neural correlate of consciousness.
5,279 citations
TL;DR: The use of spontaneous resting-state fMRI in determining functional connectivity, how functional connections tend to be related to structural connections in the brain network and how functional brain communication may form a key role in cognitive performance are discussed.
2,763 citations
TL;DR: The anatomy and function of the default network is explored across three studies to resolve divergent hypotheses about its contributions to spontaneous cognition and active forms of decision making.
2,251 citations
Cites background from "Wandering Minds: The Default Networ..."
...Associations between default network activity and spontaneous thoughts have emerged in multiple studies (e.g. McKiernan et al., 2006; Mason et al., 2007; Christoff et al., 2009)....
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...Associations between default network activity and spontaneous thoughts have emerged in multiple studies (e.g., McKiernan et al., 2006; Mason et al., 2007; Christoff et al., 2009)....
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TL;DR: It is shown that, after global signal regression, correlation values to a seed voxel must sum to a negative value and that the relative phase of global and local signals can affect connectivity measures and that, experimentally,global signal regression leads to bell-shaped correlation value distributions, centred on zero.
2,214 citations
Cites background from "Wandering Minds: The Default Networ..."
...“day-dreaming” or a “wandering mind” (Buckner et al., 2008; Mason et al., 2007)....
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...It has been hypothesized that this activation is indicative of internal monitoring, e.g. “day-dreaming” or a “wandering mind” (Buckner et al., 2008; Mason et al., 2007)....
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References
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TL;DR: A baseline state of the normal adult human brain in terms of the brain oxygen extraction fraction or OEF is identified, suggesting the existence of an organized, baseline default mode of brain function that is suspended during specific goal-directed behaviors.
Abstract: A baseline or control state is fundamental to the understanding of most complex systems. Defining a baseline state in the human brain, arguably our most complex system, poses a particular challenge. Many suspect that left unconstrained, its activity will vary unpredictably. Despite this prediction we identify a baseline state of the normal adult human brain in terms of the brain oxygen extraction fraction or OEF. The OEF is defined as the ratio of oxygen used by the brain to oxygen delivered by flowing blood and is remarkably uniform in the awake but resting state (e.g., lying quietly with eyes closed). Local deviations in the OEF represent the physiological basis of signals of changes in neuronal activity obtained with functional MRI during a wide variety of human behaviors. We used quantitative metabolic and circulatory measurements from positron-emission tomography to obtain the OEF regionally throughout the brain. Areas of activation were conspicuous by their absence. All significant deviations from the mean hemisphere OEF were increases, signifying deactivations, and resided almost exclusively in the visual system. Defining the baseline state of an area in this manner attaches meaning to a group of areas that consistently exhibit decreases from this baseline, during a wide variety of goal-directed behaviors monitored with positron-emission tomography and functional MRI. These decreases suggest the existence of an organized, baseline default mode of brain function that is suspended during specific goal-directed behaviors.
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TL;DR: Tested the 2-process theory of detection, search, and attention presented by the current authors (1977) in a series of experiments and demonstrated the qualitative difference between 2 modes of information processing: automatic detection and controlled search.
Abstract: Tested the 2-process theory of detection, search, and attention presented by the current authors (1977) in a series of experiments. The studies (a) demonstrate the qualitative difference between 2 modes of information processing: automatic detection and controlled search; (b) trace the course of the
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3,876 citations
TL;DR: This work explores the possibility that there might be a baseline or resting state of brain function involving a specific set of mental operations, including the manner in which a baseline is defined and the implications of such a baseline for the understanding ofbrain function.
Abstract: Functional brain imaging in humans has revealed task-specific increases in brain activity that are associated with various mental activities. In the same studies, mysterious, task-independent decreases have also frequently been encountered, especially when the tasks of interest have been compared with a passive state, such as simple fixation or eyes closed. These decreases have raised the possibility that there might be a baseline or resting state of brain function involving a specific set of mental operations. We explore this possibility, including the manner in which we might define a baseline and the implications of such a baseline for our understanding of brain function.
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TL;DR: The presence of self-referential mental activity appears to be associated with increases from the baseline in dorsal MPFC, and reductions in ventral MPFC occurred consistent with the fact that attention-demanding tasks attenuate emotional processing.
Abstract: Medial prefrontal cortex (MPFC) is among those brain regions having the highest baseline metabolic activity at rest and one that exhibits decreases from this baseline across a wide variety of goal-directed behaviors in functional imaging studies. This high metabolic rate and this behavior suggest the existence of an organized mode of default brain function, elements of which may be either attenuated or enhanced. Extant data suggest that these MPFC regions may contribute to the neural instantiation of aspects of the multifaceted “self.” We explore this important concept by targeting and manipulating elements of MPFC default state activity. In this functional magnetic resonance imaging (fMRI) study, subjects made two judgments, one self-referential, the other not, in response to affectively normed pictures: pleasant vs. unpleasant (an internally cued condition, ICC) and indoors vs. outdoors (an externally cued condition, ECC). The ICC was preferentially associated with activity increases along the dorsal MPFC. These increases were accompanied by decreases in both active task conditions in ventral MPFC. These results support the view that dorsal and ventral MPFC are differentially influenced by attentiondemanding tasks and explicitly self-referential tasks. The presence of self-referential mental activity appears to be associated with increases from the baseline in dorsal MPFC. Reductions in ventral MPFC occurred consistent with the fact that attention-demanding tasks attenuate emotional processing. We posit that both self-referential mental activity and emotional processing represent elements of the default state as represented by activity in MPFC. We suggest that a useful way to explore the neurobiology of the self is to explore the nature of default state activity.
2,844 citations