Thesis (Ph. D.)--University of Texas at Austin, 2002. / Supervisor: Margaret Semrud-Clikeman. Vita. Includes bibliographical references. Also available from UMI.

Thesis (Ph. D.)--University of Oregon, 2002. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 156-162). Also available for download via the World Wide Web; free to University of Oregon users.

ADHD is a childhood onset disorder with the cardinal features of inattention, impulsivity, and hyperactivity. Research has verified the validity of two subtypes of ADHD, Inattentive type (ADHD/PI) and Combined type (ADHD/C), which have unique differences in behavioral, emotional, and social impairment. The question remains, however, as to whether the ADHD subtypes actually represent two separate and distinct disorders. Results from studies examining executive functioning ability in ADHD have provided inconsistent and confusing results; however, several studies have shown poorer performance on certain measures of executive function for children with ADHD. Additional research on ADHD suggests that ADHD/PI and ADHD/C may have specific executive functioning deficits. The majority of previous research exploring the executive functioning deficits of ADHD has focused on ADHD/C or has neglected to differentiate between the subtypes, resulting in limited or inconsistent findings. Thus, the exact relationship between executive functioning and the ADHD subtypes is understudied and unclear. This study attempted to identify the differential patterns in the executive functioning of children with ADHD by subtype. Using executive functioning tasks of inhibition, planning, and working memory, this study sought to determine whether children with ADHD/C and ADHD/PI displayed unique patterns of executive functioning. Participants included 60 children aged 8-15 years who were classified into three groups: ADHD/C, ADHD/PI, and control. Results from this study revealed significantly poorer performance by the ADHD subtypes on a task of inhibition. Although analyses using the remaining tasks indicated subtype differences on planning, working memory, and inhibition/ cognitive flexibility tasks, these results were not statistically significant. Results are consistent with previous research which has also detected performance differences by the ADHD subtypes on executive functioning tasks; however, not at the clinically significant level. Analyses examining symptom severity indicated a relation between inattentive symptoms and executive functioning performance. Thus, further exploration into executive functioning within the ADHD subtypes is needed for the clarification of the neuropsychological similarities and differences of these two ADHD subtypes. Such research could assist in the establishment of effective interventions and assessment tools to aid in the earlier and more accurate identification of children with ADHD. / text

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Boys with Attention-Deficit/Hyperactivity Disorder (ADHD) were recruited from a local neuropsychology office with controls recruited from the community to assess the relationship between prenatal androgen exposure and ADHD, as well as the possible cognitive correlates of this exposure. Putative physiological markers of prenatal androgen exposure that were measured for each child included several types of otoacoustic emissions (OAEs) as well as finger-length ratios (FLRs). Neurocognitive measures included tasks which assessed components of attention, general intelligence, reading ability, and visuospatial skills. Several other variables which may also be related to androgen exposure were included (e.g., sleep disturbance, handedness, number of older brothers) in the analyses. Children ranged in age from 7 to 12 years old with 13 controls, 19 children with ADHD/Combined Type (ADHD/C), 10 with ADHD/Inattentive Type (ADHD/IA), and an additional 11 children with ADHD/IA who were rated by their parents as having relatively high levels of an experimental construct (sluggish cognitive tempo; SCT). Because more boys than girls are diagnosed with ADHD, it was hypothesized that ADHD may be associated with prenatal masculinizing hormones (i.e., androgens), and that children with ADHD would appear more masculine on markers of androgen exposure (OAEs and FLRs) than controls. However, in our current study children with ADHD did not differ from controls on these measures. There was some evidence that children with SCT may represent a more homogenous group of children within the ADHD/IA diagnostic group, and that they may share a deficit in alerting attention. Consistent with theories suggesting subtype differences in attention, children with ADHD/C did not appear to have a deficit in alerting attention, but rather appeared more cognitively impulsive and to have a deficit in auditory attention. Children with SCT were more likely to be rated by their parents as having disrupted sleep.

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Three experiments investigated the hypothesis that high doses of methylphenidate (MPH) are particularly effective in enabling boys with Attention-Deficit Hyperactivity Disorder (ADHD) to regulate the allocafion of effort and persistence under high information processing demands. In Experiment 1, the performance of boys with ADHD, ages 7 to 13, was investigated on placebo and three dosages of MPH, on a visual-memory search (VMS) task across a wide range of processing loads. Accuracy increased with dosage in a linear fashion. Findings on reaction times (RTs) revealed, however, that MPH dosage had a differential effect depending on processing load. All doses of MPH improved accuracy on low loads without a concomitant increase in processing times. When both processing load and (MPH) dosage were high, however, the ADHD boys shifted to a more cautious, time comsuming strategy, apparently in order to achieve continuing gains in accuracy. Experiment 2 compared the performance of ADHD and control boys on the VMS. It established that the ADHD group had difficulty meeting the processing demands of the VMS across all of the information loads studied, as revealed by higher error rates and slower RTs. The ADHD-control comparison also established that the effects of high doses of MPH at high loads in Experiment 1 constituted a further slowing of the ADHD boys' already slow RTs. A third, normal developmental study of boys ages 7 to 13 showed that both error rates and RTs on the VMS task decreased with age. This study also revealed considerable similarity between the performance patterns of ADHD boys and those of younger control boys on the VMS.