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

Abstract

Objective The authors examined the effect of psychostimulants on brain activity in children and adolescents with ADHD performing the Stroop Color and Word Test. Method 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. Results 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. Conclusions 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.

Understanding the Effects of Stimulant Medications on Cognition in Individuals with Attention-Deficit Hyperactivity Disorder: A Decade of Progress

“…This was interpreted as consistent with the hypothesis of ADHD-related dysfunction of the prefrontal-parietal, anterior cingulate, and cerebellar brain regions proposed based on anatomical and functional imaging studies that we outlined in the Introduction (Bush, 2010;Castellanos and Tannock, 2002b). Peterson et al (2009) used the Stroop task in an fMRI study of children without ADHD (n ¼ 20) and children with ADHD (n ¼ 16) evaluated on and off of their established clinical doses of stimulant medication. They found significant differences in brain activation for the ADHD group off medication compared with the control group, suggesting that the ADHD group was not able to suppress activity in the DMN to the same degree as the control group, and in the ADHD group medication appeared to improve the suppression of DMN activity in the ventral anterior cingulate gyrus.…”

Delay of gratification is associated with white matter connectivity in the dorsal prefrontal cortex: a diffusion tensor imaging study in chimpanzees (Pan troglodytes)

“…Results of paired-sample t-tests indicated that the number of reconstructed fibres was significantly higher in the tract from the caudate to the oPFC than the tract to the dPFC in both the right (t 48 …”

“…inattention, impulsivity, hypersensitivity to reward) [6]. Although both developmental [46,47] and pharmacological [48] studies strongly suggest a causal association, it will be imperative for future research to examine the effects of targeted interventions, with regard to generalization of DG and related abilities, as well as functional connectivity changes.…”

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

“…While in the past explanatory models have focused on localized deficits in brain regions, such as dorsal lateral prefrontal, posterior parietal, anterior cingulate cortices, within attention systems [22], more recent studies have examined the alternative possibility that attentional failures in ADHD during task performance may relate to interference by residual DMN activity [11]. Indeed, there is now compelling evidence from fMRI and electroencephalographic (EEG) studies that individuals with ADHD show excess DMN activity during tasks and that this has an adverse effect on their performance [14,[23][24][25]. While the reason for this higher DMN activity during tasks remains to be determined, one possibility is that it is due to failures of the between-network switching mechanism governed by the SN [19,26].…”