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Patients with Lesch-Nyhan disease have abnormally few dopaminergic nerve terminals and cell bodies. The abnormality involves all dopaminergic pathways and is not restricted to the basal ganglia. These dopaminergic deficits are pervasive and appear to be developmental in origin, which suggests that they contribute to the characteristic neuropsychiatric manifestations of the disease.

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We present a neuropsychological model of attention in normal and disordered states, including attention deficit hyperactivity disorder (ADHD). The model is based on a factor analysis of data derived from more than 600 children and adults. The robustness of the model is supported by its replication in a number of studies and its application in numerous investigations. It divides attention into a number of elements or factors including the capacities of encoding, focusing, and executing responses, sustaining attention, shifting attention, as well as a measure of response stability. The factors are assessed by measures derived from neuropsychological tests; we have posited a system of brain structures that maintains the elements of attention, each of which may be supported by a distinct cerebral region. We illustrate the use of the model in an investigation in progress of children referred to an inner-city family clinic for evaluation of ADHD. The ADHD study indicates that a number of aspects of attention are impaired in children diagnosed with ADHD, and that the deficient attention is probably not attributable to learning disorders. We also speculate on the possible role of immaturity of brain development in ADHD.

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Twenty-three children with autism and two control groups completed an attention battery comprising three versions of the continuous performance test (CPT), a digit cancellation task, the Wisconsin Card Sorting Test (WCST), and two novel, computerized tests of shifting attention (i.e., the Same-Different Computerized Task and the Computerized Matching Task). Children with autism could focus on a particular stimulus and sustain this focus as indicated by their performance on the digit cancellation task and the CPT. Their performance on the WCST suggested problems in some aspects of shifting attention (i.e., disengaging attention). The autism group performed as well as controls on the Same-Different Computerized Task, however, that required successive comparisons between stimuli. This implies that they could, in fact, shift their attention continuously. In addition, they did not differ from controls on the Computerized Matching Task, an analog of the WCST, suggesting that they do not have a general deficit in shifting attention.

Eighty-five non-referred school children were divided into four groups based upon the IOWA Conners Teacher's Questionnaire: pure hyperactive (HYP), pure aggressive (AGG), mixed hyperactive/aggressive (HYP/AGG), and normal controls. The groups were compared on neurobehavioral tests believed to assess inattention and impulsivity. A continuous performance test indicated that the HYP group was more inattentive than the other groups and the HYP/AGG group was most impulsive. The AGG group did not differ from controls. The data support the distinction between HYP, AGG and HYP/AGG groups of children selected by the IOWA Conners.