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: 4.69). 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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    • "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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    ABSTRACT: The default mode network (DMN) supports self-referential thought processes important for successful socialization including: theory-of-mind, episodic memory, and prospection. Connectivity between DMN's nodes, which are distributed between the frontal, temporal, and parietal lobes, change with age and may continue changing into adulthood. We have previously explored the maturation of functional connections in the DMN as they relate to autism spectrum disorder (ASD) in children 6 to 18 years of age. In this chapter, we refine our earlier study of DMN functional maturation by focusing on the development of inter-nodal connectivity in a larger pool of typically developing people 6 to 25 years of age (mean = 13.22 years ± 5.36 s.d.; N = 36; 42% female). Correlations in BOLD activity (Fisher's Z) between ROIs revealed varying strengths of functional connectivity between regions, the strongest of which was between the left and right inferior parietal lobules or IPLs (Z = 0.62 ± 0.25 s.d.) and the weakest of which was between the posterior cingulate cortex (PCC) and right middle temporal gyrus or MTG (Z = 0.06 ± 0.22 s.d.). Further, connectivity between two pairs of DMN nodes significantly increased as a quadratic function of age (p < 0.05), specifically the anterior cingulate cortex/medial prefrontal cortex (ACC/mPFC) and PCC nodes and the left IPL and right MTG nodes. The correlation between ACC/mPFC ↔ PCC connectivity and age was more significant than the correlation between left IPL ↔ right MTG connectivity and age by more than an order of magnitude. We suggest that these changes in functional connectivity in part underlie the introspective mental changes known to commonly occur between the preadolescent and adult years. A range of neurological and psychological conditions that hamper social interactions, from ASD to psychopathy, may be marked by deviations from this maturational trajectory.
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    • "The spatial pattern of the DMN could vary, corresponding to the task load (Greicius and Menon, 2004). Probably because of this, the DMN during the continuous feedback procedure mainly covered the precuneus/PCC of the reported spatial pattern (Fox et al., 2005; Damoiseaux et al., 2006). "
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    ABSTRACT: Motor feedback usually engages distinct sensory and cognitive processes based on different feedback conditions, e.g., the real and sham feedbacks. It was thought that these processes may rely on the functional connectivity among the brain networks. However, it remains unclear whether there is a difference in the network connectivity between the two feedback conditions. To address this issue, we carried out a functional magnetic resonance imaging (fMRI) study by employing a new paradigm, i.e., continuous feedback (8 min) of finger force. Using independent component analysis and functional connectivity analysis, we found that as compared with the sham feedback, the real feedback recruited stronger negative connectivity between the executive network (EN) and the posterior default mode network (pDMN). More intriguingly, the left frontal parietal network (lFPN) exhibits positive connectivity with the pDMN in the real feedback while in the sham feedback, the lFPN shows connectivity with the EN. These results suggest that the connectivity among EN, pDMN, lFPN could differ depending on the real and sham feedbacks, and the lFPN may balance the competition between the pDMN and EN, thus supporting the sensory and cognitive processes of the motor feedback.
    Neuroscience 03/2015; 289. DOI:10.1016/j.neuroscience.2014.12.075 · 3.33 Impact Factor
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    • "Changes in the functionality of the cortex at rest across the lifespan are particularly relevant to aging and neurodegeneration [23]. The resting state network (i.e., precuneus (PCu), posterior cingulate cortex (PCC), inferior parietal cortex, medial temporal lobes, medial frontal cortex, and anterior cingulate cortex [24] [25] [26], also called default mode network (DMN) [27]) is generally vulnerable to atrophy [28]. The disruption of DMN's functionality is correlated with amnestic MCI (aMCI) [29] and AD [30] and is thus related to the severity and the progression of neurodegeneration [31]. "
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    ABSTRACT: The present study investigates whether a combined cognitive and physical training may induce changes in the cortical activity as measured via electroencephalogram (EEG) and whether this change may index a deceleration of pathological processes of brain aging. Seventy seniors meeting the clinical criteria of mild cognitive impairment (MCI) were equally divided into 5 groups: 3 experimental groups engaged in eight-week cognitive and/or physical training and 2 control groups: active and passive. A 5-minute long resting state EEG was measured before and after the intervention. Cortical EEG sources were modelled by exact low resolution brain electromagnetic tomography (eLORETA). Cognitive function was assessed before and after intervention using a battery of neuropsychological tests including the minimental state examination (MMSE). A significant training effect was identified only after the combined training scheme: a decrease in the post- compared to pre-training activity of precuneus/posterior cingulate cortex in delta, theta, and beta bands. This effect was correlated to improvements in cognitive capacity as evaluated by MMSE scores. Our results indicate that combined physical and cognitive training shows indices of a positive neuroplastic effect in MCI patients and that EEG may serve as a potential index of gains versus cognitive declines and neurodegeneration.
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