Differential measures of ‘sustained-attention’ in children with attention-deficit/hyperactivity or tic disorders : relationship to monoamine metabolism
Introduction: Controversy exists on whether the constructs related to sustained attention and tested by paper/pencil tasks and computerized continuous-performance-tests (CPT) are similar, and whether the deficits recorded in children with attention-deficit/hyperactivity symptoms (ADHD) using these different forms of testing information processing are comparable. Methods: Signal-detection measures (d-prime and beta-criterion) and type of error were recorded on four such tests of 'sustained attention', with increasing working-memory requirements (respond to 'x', respond to 'x' only after 'a') in healthy children (n = 14, mean 10 years of age), and those with ADHD (n = 14, mean 10 years of age) or a tic syndrome (TS, n = 11, mean 11 years of age). Clinical associations were sought from 24h-urinary measures of monoamine activity (parent amines and metabolites), - dopamine (DA), HVA, noradrenaline (NA), MHPG, serotonin (5-HT), 5-HIAA. Results: The cancellation paper/pencil test revealed no group differences for errors or signal detection measures. In contrast, on the CPTx ADHD children made more omission and commission errors than controls, but TS children made mostly omissions. This reflected the poor perceptual sensitivity (d-prime, d') for ADHD and conservative response criteria (beta) for TS children. This group difference extended to the CPT ax which was shown on a regression analysis to test for putative working-memory-related abilities as well as concentration. In all children immediate response-feedback (vs. feedback at the end of the test) reduced omissions, and modestly improved d'. CPT ax performance related negatively to dopamine metabolism in controls and to serotonin metabolism in the ADHD group. But comparisons between the metabolites in the ADHD group suggest that increased serotonin- and decreased noradrenaline- with respect to dopamine-metabolism may detract from CPT performance in terms of d-prime. Conclusions: CPT tasks demonstrated a perceptual-based impairment in ADHD and response conservatism in TS patients independent of difficulty. Catecholamine activity was implicated in the promotion of perceptual processing in normal and ADHD children, but serotonin activity may contribute to poor CPTax performance (emphasis on working-memory function) in ADHD patients
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