ADHD Impairment Research Articles

Attention and Neurocognitive Impairment in ADHD

Specific executive functions (EFs) and attention deficit patterns in ADHD subtypes were studied in 50 boys (ages 8-14 years, mean 10.42) with ADHD and 44 controls, at the University of Rome, Italy.

Neuropsychological functioning in people with ADHD across the lifespan

ADHD is defined by behavioral characteristics similar to neuropsychological disorders of executive dysfunction. This paper is a literature review of the neurocognitive characteristics of ADHD from early childhood through adulthood. The author addresses the development of the concept of attention and executive function (EF) deficits in ADHD, clinical neuropsychological studies of pre-teenage children, teenagers and adults with ADHD, gender and the role of psychiatric co-morbidity including the relationship of learning disabilities to ADHD, heterogeneity of neuropsychological dysfunctions, experimental neuropsychological studies, the relationship of brain structure to function, psychopharmacology of ADHD, and clinical neuropsychological assessment. The group data clearly supports the hypothesis that executive dysfunctions are correlates of ADHD regardless of gender and age, and these EF deficits are exacerbated by co-morbidity with learning disabilities such as dyslexia. However, there is limited data on children under the age of 5, teenagers from age 13–18, and adults with ADHD over the age of 40. Studies of individual classification of people with ADHD compared to healthy, non-psychiatric controls do not support the use of neuropsychological tests for the clinical diagnosis of ADHD, and indicate that not all persons with ADHD have EF deficits. Some persons with ADHD may have deficits in brain reward systems that are relatively independent of EF impairments. Future research should clarify the multiple sources of ADHD impairments, continue to refine neuropsychological tools optimized for assessment, and incorporate longitudinal, developmental designs to understand ADHD across the lifespan.

Differential measures of ‘sustained attention’ in children with attention-deficit/hyperactivity or tic disorders: relations to monoamine metabolism

Controversy exists on whether the constructs tested by paper/pencil and computerized continuous-performance tests (CPT) are similar, and the deficits recorded in children with attention-deficit/hyperactivity symptoms (ADHD) are comparable. Signal-detection measures were recorded on four such tests of ‘sustained attention’, with increasing working-memory requirements in healthy children (14; mean 10 years), and those with ADHD (14; mean 10 years) or a tic syndrome (TS, 11; mean 11 years). Clinical associations were sought from 24-h urinary measures of monoamine activity. The cancellation paper/pencil test revealed no group differences for errors or signal detection measures. On the CPT, ADHD children made more omission and commission errors than control subjects, but TS children made mostly omissions. This reflected the poor perceptual sensitivity ( d-prime, d′) for ADHD and conservative response criteria (β) for TS children. This group difference extended to the CPTax, 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 reduced omissions, and modestly improved d′. CPTax performance related negatively to dopamine metabolism in control subjects 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′. 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 (working-memory) performance in ADHD patients.