THE STRIATUM IN A PUTATIVE CEREBRAL NETWORK ACTIVATED BY VERBAL AWARENESS IN NORMALS AND IN ADHD CHILDREN

The aim of the present study was to evaluate the striatum's involvemen t 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 act ivation in response to tasks requiring verbal awareness. Regional cere bral blood flow (rCBF) was studied with the Xenon(133) 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 t he semantic processing (Passive Listening - White Noise) and supra-mod al attention components (Detection of Targets - Passive Listening of v erbal awareness). ADHD children had decreased rCBF in the right striat um when compared to normals (mean difference from grand mean of each s ubject 8.06 ml/100/g/min vs 14.16 ml/100/g/min, p < 0.05). Factor anal ysis of the rCBF data revealed high factor I loadings for the frontal and striatal regions, which, in conjunction with the nature of the exp erimental conditions supported the inference that factor I mediated ve rbal awareness. Factor scores, which summarized the activity of all of the regions of interest (ROI's) on factor I, were differentially affe cted by the language component of the experimental tasks. Function sco res were derived from factor I for the anterior cingulum and infero-fr ontal 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 th e language demands of the tasks. However, the striatum demonstrated re duced function scores ( p, 0.05) in ADHD for all tasks. Our finding th at the anterior gyrus cinguli were activated by supramodal attention a nd that the infero-frontal and striatal regions were activated by sema ntic processing supports the involvement of these ROI's in verbal awar eness. Furthermore, the depressed functional contribution of the stria tum to verbal awareness in ADHD children is consistent with and helps to explain their reduced cognitive control over behaviour and mental f unction.