Article

An fMRI Study of the Effects of Psychostimulants on Default-Mode Processing During Stroop Task Performance in Youths With ADHD

Department of Biological and Medical Psychology, University of Bergen, Bergen, Hordaland, Norway
American Journal of Psychiatry (Impact Factor: 13.56). 09/2009; 166(11):1286-94. DOI: 10.1176/appi.ajp.2009.08050724
Source: PubMed

ABSTRACT The authors examined the effect of psychostimulants on brain activity in children and adolescents with ADHD performing the Stroop Color and Word Test.
The authors acquired 52 functional MRI scans in 16 youths with ADHD who were known responders to stimulant medication and 20 healthy comparison youths. Participants with ADHD were scanned on and off medication in a counterbalanced design, and comparison subjects were scanned once without medication.
Stimulant medication significantly improved suppression of default-mode activity in the ventral anterior cingulate cortex in the ADHD group. When off medication, youths with ADHD were unable to suppress default-mode activity to the same degree as comparison subjects, whereas when on medication, they suppressed this activity to comparison group levels. Greater activation of the lateral prefrontal cortex when off medication predicted a greater reduction in ADHD symptoms when on medication. Granger causality analyses demonstrated that activity in the lateral prefrontal and ventral anterior cingulate cortices mutually influenced one another but that the influence of the ventral anterior cingulate cortex on the lateral prefrontal cortex was significantly reduced in youths with ADHD off medication relative to comparison subjects and increased significantly to normal levels when ADHD youths were on medication.
Psychostimulants in youths with ADHD improved suppression of default-mode activity in the ventral anterior cingulate and posterior cingulate cortices, components of a circuit in which activity has been shown to correlate with the degree of mind-wandering during attentional tasks. Stimulants seem to improve symptoms in youths with ADHD by normalizing activity within this circuit and improving its functional interactions with the lateral prefrontal cortex.

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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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    • "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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    • "The default mode network is implicated in ADHD (Fair et al., 2010) and is associated with poorer attentional regulation in ADHD (Castellanos et al., 2008). Further, pharmacological interventions that improve ADHD symptoms normalize activity within this network (Liddle et al., 2011; Peterson et al., 2009). One proposed mechanism of mindfulness is reduced activity and altered connectivity in this network (Sood & Jones, 2013). "
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