A lack of default network suppression is linked to increased distractibility in ADHD. Brain Research, 1273, 114-128

M.I.N.D. Institute, Department of Psychiatry and Behavioral Sciences, University of California Davis Medical School, 2825 50th St., Sacramento, CA 95817, USA.
Brain research (Impact Factor: 2.84). 04/2009; 1273:114-28. DOI: 10.1016/j.brainres.2009.02.070
Source: PubMed

ABSTRACT Heightened distractibility in participants with ADHD as indexed by increased reaction time (RT) variability has been hypothesized to be due to a failure to sufficiently suppress activation in the default attention network during cognitively demanding situations. The present study utilized fMRI to examine the relationship between intra-individual variability (IIV) in task RT and suppression of BOLD response in regions of the default network, using a working memory paradigm and two levels of control tasks. IIV was calculated separately for thirteen healthy control and twelve children with ADHD, Combined Type. Children with ADHD displayed significantly more RT variability than controls. Neural measures showed that although both groups displayed a pattern of increasing deactivation of the medial prefrontal cortex (PFC) with increasing task difficulty, the ADHD group was significantly less deactive than controls. Correlations between IIV and brain activation suggested that greater variability was associated with a failure to deactivate ventromedial PFC with increasing task difficulty. T-tests on brain activation between participants with ADHD with low versus high IIV implicated a similar region so that high variability was associated with greater activity in this region. These data provide support for the theory that increased distractibility in at least some participants with ADHD may be due to an inability to sufficiently suppress activity in the default attention network in response to increasing task difficulty.

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Available from: Julie B Schweitzer, Sep 26, 2015
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    • "literature (Fassbender et al., 2009; Liddle et al., 2011), as well as the default mode interference hypothesis (DMI; Sonuga-Barke and Castellanos, 2007), which predicts periodic attentional lapses (e.g. periodic clusters of longer reaction time or increased performance errors) when default activity persists during a task. "
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    • "Indeed the degree of attenuation of VLF oscillations in the DMN has been suggested to reflect the amount of mental effort or sustained attention required by a task (Fassbender et al., 2009). Empirical evidence suggests that task-related attenuation of VLF oscillations is more prominent during challenging tasks, whereas it is reduced during well-practiced or low attention demanding tasks (Fassbender et al., 2009; Jolles et al., 2010; Singh and Fawcett, 2008). While resting, subjects often " tune out " their attention from external stimuli and become more internally focused. "
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    • "On the other hand, DMN attenuation following the onset of goal-directed tasks appears to be necessary for effective switching from resting to working brain states (Fox et al., 2005; Greicius et al., 2003; Raichle and Snyder, 2007): Excess DMN activity when individuals are working on laboratory information processing tasks during fMRI studies is associated with performance deficits (Sonuga-Barke and Castellanos, 2007; Weissman et al., 2006). Individuals with ADHD fail to effectively suppress the DMN activity during cognitive task performance (Fassbender et al., 2009; Peterson et al., 2009), which may explain patterns of ADHDrelated periodic attentional lapses and intra-individual reaction time variability (Helps et al., 2011). Compared to fMRI BOLD signals, which map neural activity by imaging haemodynamic responses, DC-EEG offers a more direct measure of spontaneous VLF oscillations (VLFOs), albeit with relatively limited spatial resolution. "
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    ABSTRACT: Background: Spontaneous very low frequency oscillations (VLFO), seen in the resting brain, are attenuated when individuals are working on attention demanding tasks or waiting for rewards (Hsu et al., 2013). Individuals with attention-deficit/hyperactivity disorder (ADHD) display excess VLFO when working on attention tasks. They also have difficulty waiting for rewards. Here we examined the waiting brain signature in ADHD and its association with impulsive choice. Methods: DC-EEG from 21 children with ADHD and 21 controls (9-15 years) were collected under four conditions: (i) resting; (ii) choosing to wait; (iii) being "forced" to wait; and (iv) working on a reaction time task. A questionnaire measured two components of impulsive choice. Results: Significant VLFO reductions were observed in controls within anterior brain regions in both working and waiting conditions. Individuals with ADHD showed VLFO attenuation while working but to a reduced level and none at all when waiting. A closer inspection revealed an increase of VLFO activity in temporal regions during waiting. Excess VLFO activity during waiting was associated with parents' ratings of temporal discounting and delay aversion. Conclusions: The results highlight the potential role for waiting-related spontaneous neural activity in the pathophysiology of impulsive decision-making of ADHD.
    Developmental Cognitive Neuroscience 01/2015; 29. DOI:10.1016/j.dcn.2015.01.007 · 3.83 Impact Factor
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