Article

Default-Mode Activity during a Passive Sensory Task: Uncoupled from Deactivation but Impacting Activation

Department of Neurology, Stanford University School of Medicine, CA 94301-5719, USA.
Journal of Cognitive Neuroscience (Impact Factor: 4.09). 12/2004; 16(9):1484-92. DOI: 10.1162/0898929042568532
Source: PubMed

ABSTRACT

Deactivation refers to increased neural activity during low-demand tasks or rest compared with high-demand tasks. Several groups have reported that a particular set of brain regions, including the posterior cingulate cortex and the medial prefrontal cortex, among others, is consistently deactivated. Taken together, these typically deactivated brain regions appear to constitute a default-mode network of brain activity that predominates in the absence of a demanding external task. Examining a passive, block-design sensory task with a standard deactivation analysis (rest epochs vs. stimulus epochs), we demonstrate that the default-mode network is undetectable in one run and only partially detectable in a second run. Using independent component analysis, however, we were able to detect the full default-mode network in both runs and to demonstrate that, in the majority of subjects, it persisted across both rest and stimulus epochs, uncoupled from the task waveform, and so mostly undetectable as deactivation. We also replicate an earlier finding that the default-mode network includes the hippocampus suggesting that episodic memory is incorporated in default-mode cognitive processing. Furthermore, we show that the more a subject's default-mode activity was correlated with the rest epochs (and "deactivated" during stimulus epochs), the greater that subject's activation to the visual and auditory stimuli. We conclude that activity in the default-mode network may persist through both experimental and rest epochs if the experiment is not sufficiently challenging. Time-series analysis of default-mode activity provides a measure of the degree to which a task engages a subject and whether it is sufficient to interrupt the processes--presumably cognitive, internally generated, and involving episodic memory--mediated by the default-mode network.

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    ABSTRACT: In the absence of stimulus or task, the cortex spontaneously generates rich and consistent functional connectivity patterns (termed resting state networks) which are evident even within individual cortical areas. We and others have previously hypothesized that habitual cortical network activations during daily life contribute to the shaping of these connectivity patterns. Here we tested this hypothesis by comparing, using blood oxygen level-dependent-functional magnetic resonance imaging, the connectivity patterns that spontaneously emerge during rest in retinotopic visual areas to the patterns generated by naturalistic visual stimuli (repeated movie segments). These were then compared with connectivity patterns produced by more standard retinotopic mapping stimuli (polar and eccentricity mapping). Our results reveal that the movie-driven patterns were significantly more similar to the spontaneously emerging patterns, compared with the connectivity patterns of either eccentricity or polar mapping stimuli. Intentional visual imagery of naturalistic stimuli was unlikely to underlie these results, since they were duplicated when participants were engaged in an auditory task. Our results suggest that the connectivity patterns that appear during rest better reflect naturalistic activations rather than controlled, artificially designed stimuli. The results are compatible with the hypothesis that the spontaneous connectivity patterns in human retinotopic areas reflect the statistics of cortical coactivations during natural vision.
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    • "DMN activity attenuates following engagement with tasks requiring externally orientated, goal-directed attention. The degree of attenuation (i) varies as a function of cognitive load (Greicius et al. 2003; McKiernan et al. 2003; Greicius & Menon, 2004; Fransson, 2006; Singh & Fawcett, 2008; Pyka et al. 2009) and (ii) is predictive of performance deficits linked to residual task-related DMN activity (Weissman et al. 2006; Li et al. 2007; Sonuga-Barke & Castellanos, 2007). Consistent with the default mode interference hypothesis (SonugaBarke & Castellanos, 2007) there is evidence of DMN hyperactivation during task performance in individuals with ADHD (Fassbender et al. 2009; Peterson et al. 2009; Helps et al. 2010; Liddle et al. 2011). "
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    • "The majority of cortical synapses forms between childhood and adulthood and follow a quadratic trajectory similar to the ones observed for functional connectivity observed above (Giedd et al., 1999; Gogtay et al., 2004). DMN is a network implicated in self-reflective thought processes crucial for socialization (Addis et al., 2007; Buckner et al., 2008; Greicius and Menon 2004; Kim 2010; Kim et al., 2010; Spreng and Grady 2010). Finding a maturational trajectory that extends from childhood to young adulthood, parallels synaptogenesis, and forms between two of DMN's key nodes suggests that this connectivity reflects maturational increases in self-reflective thought processes. "
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