A lack of default network suppression is linked to increased distractibility in ADHD

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.

“Can waiting awaken the resting brain?” A comparison of waiting- and cognitive task-induced attenuation of very low frequency neural oscillations

“…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.…”

“…This has been demonstrated using a broad range of cognitive tasks including those involving response inhibition (Liddle et al, 2011) and working memory (Fassbender et al, 2009) measured with both functional magnetic resonance imaging (fMRI; Fransson, 2006;Liddle et al, 2011) and electroencephalography (EEG; Broyd, Helps, & Sonuga-Barke, 2011;Helps, Broyd, James, Karl, & Sonuga-Barke, 2009). Moreover, this task-induced attenuation of VLF oscillations appears to occur irrespective of task content (Fox et al, 2005) although the extent of attenuation is related to task difficulty (Fassbender et al, 2009;Gilbert et al, 2012;Singh and Fawcett, 2008). Notably, persisting VLF oscillations in the DMN during the completion of a goal-directed cognitive task have been proposed as a major source of attentional lapses which constrain cognitive performance (Sonuga-Barke and Castellanos, 2007).…”

“…For example, patients with ADHD exhibit altered functional connectivity at rest and during task performance. They also display reduced task-induced attenuation of VLF oscillations in regions linked to DMN (Castellanos et al, 2008;Fair et al, 2010;Fassbender et al, 2009;Liddle et al, 2011;Tian et al, 2008). In line with neuroimaging findings, studies with DC-EEG have found reduced resting state VLF EEG power in adolescents with ADHD, along with decreased rest-to-task attenuation of VLF EEG power compared to healthy age-matched volunteers (Helps et al, 2010).…”

“…Notably, persisting VLF oscillations in the DMN during the completion of a goal-directed cognitive task have been proposed as a major source of attentional lapses which constrain cognitive performance (Sonuga-Barke and Castellanos, 2007). For instance, reduced task-induced attenuation of resting VLF oscillations in DMN regions is associated with increased response times (Weissman et al, 2006) and elevated response variability (Fassbender et al, 2009). …”

Altered intrinsic organisation of brain networks implicated in attentional processes in adult attention-deficit/hyperactivity disorder: a resting-state study of attention, default mode and salience network connectivity

“…This means that effective attentional engagement requires both -the "switching on" of the task-positive attention networks and the "switching off" of the DMN [10][11][12]. Indeed, there is compelling evidence that performance suffers when excess (residual) DMN activity is observed during attention demanding tasks [12][13][14].…”