Relationship between central serotonergic function and aggression in prepubertal boys: effect of age and attention-deficit/hyperactivity disorder.

Data indicate that diminished central serotonergic (5-HT) function is related to aggression in adults, but discrepant findings in children suggest that age or the presence of attention-deficit/hyperactivity disorder (ADHD) may influence this relationship. This study examined whether age or ADHD affects the association between 5-HT and aggression in 7-11-year old clinically-referred boys. Forty-six boys were divided into non-aggressive ADHD, aggressive ADHD, and aggressive non-ADHD groups based on responses to interviews and ratings of behavior. Central 5-HT function was assessed by measuring the prolactin response to a 1-mg/kg oral dose of D,L-fenfluramine. There was no significant difference in the prolactin response across the three groups of boys. Furthermore, when examined dimensionally, prolactin response was largely unrelated to ratings of aggression, even after controlling for ADHD. Finally, age was not associated with prolactin response, and had no effect on the relationship between prolactin response and aggression. This study provides further evidence that there is no clear relationship between central 5-HT function and aggression in disruptive boys. Moreover, these data do not confirm the hypothesis that age or the presence of ADHD influence the relationship between 5-HT and childhood aggression.

The neurobiology of attention-deficit hyperactivity disorder.

Attention-deficit hyperactivity disorder is a childhood psychiatric disorder characterized by inattention, impulsivity, and overactivity. Considerable research has focused on the neurobiological substrates of this disorder. Although the specific nature of the brain dysfunction remains elusive, progress has been made and several models of the underlying pathophysiology have been suggested. Research in the fields of neuropsychology, neuroimaging, neurochemistry, and molecular genetics, which points to a multifactorial etiology for the disorder, is reviewed. While several inconsistencies exist across studies, evidence supports dysfunction of fronto-striatal dopaminergic and noradrenergic circuits with resultant executive deficits in cognitive functioning.

Neurobiological models of attention-deficit/hyperactivity disorder: a brief review of the empirical evidence.

Attention-deficit/hyperactivity disorder (ADHD) is a psychiatric disorder characterized by inattention, impulsivity, and overactivity that begins in childhood. While considerable research has focused on the neurobiological substrates of this disorder, the specific nature of the brain dysfunction in ADHD has remained elusive. However, early data from pharmacological treatment studies, as well as from basic research in animals and humans, initially led several investigators to develop neurobiological models of ADHD. These models of ADHD and more recent evidence from neuropsychological, neuroimaging, neurochemical, and genetic research are briefly reviewed. While not completely consistent, the empirical data suggest that dysfunction in prefrontal-striatal neural circuits, as well as in brain stem catecholamine systems that innervate these circuits, may underlie the executive function deficits in ADHD.

Predictors of physical aggression in children with attention-deficit/hyperactivity disorder.

The present investigation examined factors that predict physical aggression in children with attention-deficit/hyperactivity disorder (ADHD). Stepwise, multiple regression-analyses were used to examine predictors of children's physical aggression as rated by parents at a 1-year follow-up point and by teachers at both 1- and 2-year follow-up points. Early parent and teacher ratings of verbal aggression (ie, cursing, teasing, and threatening) accounted for the greatest proportion of the variance in physical aggression ratings obtained at follow-up. None of the other predictor variables, including early ratings of physical aggression and ADHD behaviors, contributed significant additional variance beyond that accounted for by early verbal aggression ratings. Temporal and cross-informant analyses revealed that the relationship between verbal aggression and later physical aggression was situation-specific for teacher ratings but not parent ratings. Although physical aggression may emerge early in development, these data suggest that verbal aggression represents a stable, temperamental characteristic that may be of greater value than early physical aggression for predicting later physically aggressive acts.

Neurocognitive functioning in adults with attention-deficit/hyperactivity disorder.

The performance of nine adults with attention-deficit/hyperactivity disorder (ADHD) was compared with the performance of 23 normal controls on computerized measures of target orientation, sustained attention, encoding speed, and motor output/response organization to determine the nature of the neurocognitive deficits of adults with ADHD. While the groups' performances on measures of sustained attention and encoding speed did not differ, significant group differences were seen on a task that targeted motor output/response organization. These data suggest that the neurocognitive difficulties of ADHD adults are not related to a primary deficit in sustained attentional functioning. Rather, the deficient information processing in ADHD adults is related to difficulties with motor output/response organization.

Identification of AD/HD subtypes using laboratory-based measures: a cluster analysis.

The current investigation used laboratory-based measures of inattention, impulsivity, and activity level to identify subgroups of children with attention-deficit/hyperactivity disorder (AD/HD). Data derived from solid state actigraphs and a continuous performance test (CPT) were obtained from a clinically referred sample and submitted to a cluster analysis. These empirically derived groups were then evaluated for clinical relevance and subsequently validated by parent and teacher ratings and tests of intellectual functioning and academic achievement. Four distinct subgroups emerged: Hyperactive-inattentive (HYP-IN), impulsive-inattentive (IMP-IN), inattentive only, and hyperactive only. The HYP-IN group was impaired on measures of intellectual functioning and academic achievement relative to the other three groups. In contrast, the IMP-IN group was generally rated as more aggressive, although this difference was not statistically significant for all measures. The data suggest that the augmentation of clinical descriptors with laboratory-based data may be an effective strategy by which to categorize diagnostic subgroups of AD/HD.