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.