The striatum in a putative cerebral network activated by verbal awareness in normals and in ADHD children

Abstract

The aim of the present study was to evaluate the striatum's involvement in verbal awareness (semantic processing and supra-modal attention) in normals and children with attention deficit hyperactivity disorder (ADHD). Our previous finding of striatal hypoperfusion in ADHD at rest, supports our prediction that the striatum will also show reduced activation in response to tasks requiring verbal awareness. Regional cerebral blood flow (rCBF) was studied with the Xenon133 SPECT method in 12 boys with ADHD and six normal controls. The experimental controls included: (1) White Noise, (2) Passive Listening to a series of animal names, and (3) Detection of Targets ("dangerous animals") from the same series of animal names. The conditions were selected to isolate the semantic processing (Passive Listening - White Noise) and supra-modal attention components (Detection of Targets - Passive Listening of verbal awareness). ADHD children had decreased rCBF in the right striatum when compared to normals (mean difference from grand mean of each subject 8.06 ml/100 g/min vs 14.16 ml/100 g/min, p < 0.05). Factor analysis of the rCBF data revealed high factor I loadings for the frontal and striatal regions, which, in conjunction with the nature of the experimental conditions supported the inference that factor I mediated verbal awareness. Factor scores, which summarized the activity of all of the regions of interest (ROI's) on factor I, were differentially affected by the language component of the experimental tasks. Function scores were derived from factor I for the anterior cingulum and infero-frontal regions to evaluate their respective involvement in supra-modal attention and semantic processing. Function scores were also developed for the striatum, because of its central location and potential role in ADHD. The anterior cingulum was activated by supra-modal attention. The infero-frontal and the striatal regions were both activated by the language demands of the tasks. However, the striatum demonstrated reduced function scores (p < 0.05) in ADHD for all tasks. Our finding that the anterior gyrus cinguli were activated by supramodal attention and that the infero-frontal and striatal regions were activated by semantic processing supports the involvement of these ROI's in verbal awareness. Furthermore, the depressed functional contribution of the striatum to verbal awareness in ADHD children is consistent with and helps to explain their reduced cognitive control over behaviour and mental function.

ADHD: increased dopamine receptor availability linked to attention deficit and low neonatal cerebral blood flow

“…pB, raclopride binding potential. A second line of evidence for deficiency in dopaminergic pathways was the early demonstration with 133 Xe in single PET of dysfunctional striatum in ADHD (Lou et al 1984), confirmed in an independent patient group (Lou et al 1998). This discovery established ADHD as the first member of a class of neurodevelopmental disorders of frontal-subcortical-cortical circuits controlling behaviour.…”

Effects of methylphenidate on resting-state brain activity in normal adults: an fMRI study

“…For instance, striatal hypoperfusion is found in ADHD at rest using SPECT, and the right striatum has low activation in a verbal awareness task in ADHD [80] . In a stop signal task, patients show lower power of response in the left caudate [10] .…”

Depressed Dopamine Activity in Caudate and Preliminary Evidence of Limbic Involvement in Adults With Attention-Deficit/Hyperactivity Disorder

“…9 As discussed earlier, there is also evidence of disruption in DAT levels in subjects with ADHD, although the findings are inconsistent (reviewed 5 ) and difficult to interpret because DAT levels are a function of both the density of DA terminals and the number of DATs per terminal. Decreased DA release could also reflect prefrontal pathology, which has been consistently documented in ADHD (reviewed 28,29 ) since frontal-striatal glutamatergic circuits regulate striatal DA release. 30,31 However, prefrontal pathology in ADHD could also indicate improper dopaminergic regulation of frontal regions.…”