Search

Objective: Recent studies have suggested that attention deficit hyperactivity disorder (ADHD) is associated with abnormalities in basal ganglia and prefrontal cortical functioning. However, these studies have primarily relied upon cognitive tasks that reflect impulse control rather than attentional mechanisms., Method: The authors used functional magnetic resonance imaging to investigate the neural correlates of selective and divided attention in a randomized, double-blind, placebo-controlled pharmacological challenge with methylphenidate in 15 adolescents with ADHD (ages 14-17), eight adolescents with reading disorder (ages 12-17), and four adolescents with both reading disorder and ADHD (ages 14-18) who were scanned during both a methylphenidate and a placebo session. Fourteen healthy comparison subjects (ages 12-20) who were not given methylphenidate served as the primary comparison group., Results: During the divided attention task, unmedicated subjects with ADHD or reading disorder recruited the left ventral basal ganglia significantly less than the healthy comparison subjects. Methylphenidate led to an increase in activation in this region but had no effect on task performance. Subjects with ADHD also recruited the middle temporal gyrus significantly less than the comparison subjects, but methylphenidate did not have a direct effect on activation in this region., Conclusions: These results suggest that ADHD is associated with abnormal processing in attentional networks, with specific dysfunction in striatal circuitry. Methylphenidate may act to normalize activity within this network.

Children referred to the Learning Disorders Unit of the Yale-New Haven Hospital were evaluated for indications of prenatal exposure to ethanol. Our results suggest a continuum of teratogenic effects of ethanol on the central nervous system. Journal availability The C. V. Mosby Co., 11830 Westline Industrial Dr., St. Louis, MO 63141. (Author)

In this review, we focus on those studies using brain imaging modalities to examine children and adults with attention-deficit hyperactivity disorder (ADHD). The conceptualization of attention that frames our review stresses the adaptive function of attention systems in regulating and orchestrating operations of multiple processing systems to satisfy multiple and sometimes inconsistent goals, and to maintain behavioral coherence. More specifically, we postulate that attention should be conceptualized as consisting of multiple control systems, each of which is associated with a different repertoire of behaviors. A reasonable starting point is the posterior and anterior attentional systems proposed by Posner and associates. Recent functional brain imaging studies support such a notion, with perceptual selection involving the posterior system and executive function engaging distinct anterior frontal regions. To date, the morphometric studies as well as more recent functional imaging studies suggest that subjects with ADHD differ from controls primarily in more anterior brain regions as well as in anterior-striatal systems. Studies now in progress offer the promise of examining neural systems throughout the brain in individuals with ADHD, neural systems involving both anterior as well as posterior attentional systems. Although attention as a construct and ADHD as a disorder were historically described for the first time in the mid-to-late 19th century, it is now apparent that, despite the great progress within the last 4 decades, a full understanding of the neurobiology of ADHD must await the 21st century. MRDD Research Reviews 1999;5:185–190. © 1999 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Background Functional connectivity analyses of functional magnetic resonance imaging data are a powerful tool for characterizing brain networks and how they are disrupted in neural disorders. However, many such analyses examine only one or a small number of a priori seed regions. Studies that consider the whole brain frequently rely on anatomic atlases to define network nodes, which might result in mixing distinct activation timecourses within a single node. Here, we improve upon previous methods by using a data-driven brain parcellation to compare connectivity profiles of dyslexic (DYS) versus nonimpaired (NI) readers in the first whole-brain functional connectivity analysis of dyslexia. Methods Whole-brain connectivity was assessed in children ( n = 75; 43 NI, 32 DYS) and adult ( n = 104; 64 NI, 40 DYS) readers. Results Compared to NI readers, DYS readers showed divergent connectivity within the visual pathway and between visual association areas and prefrontal attention areas; increased right-hemisphere connectivity; reduced connectivity in the visual word-form area (part of the left fusiform gyrus specialized for printed words); and persistent connectivity to anterior language regions around the inferior frontal gyrus. Conclusions Together, findings suggest that NI readers are better able to integrate visual information and modulate their attention to visual stimuli, allowing them to recognize words on the basis of their visual properties, whereas DYS readers recruit altered reading circuits and rely on laborious phonology-based "sounding out" strategies into adulthood. These results deepen our understanding of the neural basis of dyslexia and highlight the importance of synchrony between diverse brain regions for successful reading. [ABSTRACT FROM AUTHOR]