Imaging the ADHD brain: Disorder-specificity, medication effects and clinical translation
Author: Katya Rubia, Analucia A. Alergia, Helen Brinson Publisher: https://www.researchgate.net/publication/261747133_Imaging_the_ADHD_brain_Disorder-specificity_medication_effects_and_clinical_translation Publish Date: 2014-4 Review Date: Status:💥
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The
only enhanced GM volume in the meta-analysis of Nakao
et al. [26] in ADHD patients relative to controls was in the pre-cuneus, which is part of the default mode network (DMN).
The DMN consists of intercorrelated coactivation of medial
frontal lobe, anterior and posterior cingulate and inferior tem-poral and parietal areas during rest that are parametrically attenu-ated during cognitive load, presumably reflecting increases in
attentional and computational resources that impinge upon
task-unrelated thoughts and processes. The DMN is therefore
thought to reflect self-referential and stimulus-independent
thought processes that need to be switched off for successful cog-nitive functioning, which is shown by increased attentional lapses
being associated with failure to inhibit the DMN [29]. ADHD
patients have shown to have more attentional lapses and attenu-ated deactivation of the DMN during attention tasks [30–32].
The enlarged volume size may hence potentially be a plastic
consequence of enhanced DMN activation (i.e., diminished
deactivation).
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Functional MRI studies
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Functional MRI (fMRI) studies have provided consistent evi-dence for fronto-striatal, fronto-parietal and fronto-cerebellar
deficits in ADHD during tasks of cognitive control. Further-more, there is some emerging, but less consistent evidence for
fronto-limbic abnormalities in the context of reward processing.
Several meta-analyses of whole-brain fMRI studies of EF and
timing tasks have been published recently. They showed cogni-tive domain-specific fronto-striatal, fronto-parietal and fronto-cerebellar brain dysfunctions in ADHD. Thus, a meta-analysis
of 21 whole-brain fMRI studies of cognitive and motor inhibi-tion, including 7 adult and 14 pediatric studies, showed that
287 ADHD patients relative to 320 healthy controls had con-sistently reduced activation in key regions of motor response
inhibition, in right IFC, supplementary motor area (SMA),
ACC, left striatum and right thalamus (FIGURE 1 A)[51]. When
inhibition tasks were split into motor response and interference
inhibition, the reduced activations were more prominently right
hemispheric and in the SMA for motor response inhibition,
while for tasks of interference inhibition, left ACC dysfunction
was more prominent in line with the prominent role of the
SMA for motor inhibition and the ACC for interference inhi-bition, respectively [51]. A meta-analysis on attention tasks
included mostly 13 pediatric whole-brain fMRI studies on a
relatively wide range of attention tasks such as selective, divided
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corroborate this hypothesis.
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The timing meta-analysis in addi-tion also showed increased activation in ADHD patients in
default mode regions, the PCC and precuneus (FIGURE 1 C)[31].
This was also found in a parametric task design fMRI study
where ADHD adolescents, unlike controls, did not progres-sively deactivate the precuneus with increasing attention load;
and furthermore, this was inversely associated with performance
and decreased fronto-striatal activation [30]. Problems to deacti-vate the DMN have been associated with more attention lapses,
both in normal development and in ADHD [32] and could also
reflect a developmentally delayed stage in attention process-i ng[4]. Both the problematic deactivation of the DMN con-comitant with poor activation of task relevant and age-correlated brain activation may hence reflect a developmental
delay of brain function and both are likely underlying the poor
performance in ADHD on attention-demanding higher level
cognitive tasks.
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- Broyd SJ, Demanuele C, Debener S, et al.
Default-mode brain dysfunction in mental
disorders: a systematic review. Neurosci
Biobehav Rev 2009;33(3):279-96
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enhanced activation was
observed predominantly in default mode regions as well as in
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there is
evidence for abnormally enhanced gray matter and function in
posterior regions of the default mode network. Evidence for
reduced anticorrelation between task-positive fronto-striatal/
fronto-cerebellar networks and the default mode network
suggests that both poor task-positive activation and reduced
deactivation of the default mode network underlie poor cognitive
functioning in ADHD.