title: Attention deficit/hyperactivity disorder: a focused overview for children's environmental health researchers.
abstract: OBJECTIVE
  Attention deficit/hyperactivity disorder (ADHD) is the most frequently diagnosed childhood neurobehavioral disorder. Much research has been done to identify genetic, environmental, and social risk factors for ADHD; however, we are still far from fully understanding its etiology. In this review we provide an overview of diagnostic criteria for ADHD and what is known about its biological basis. We also review the neuropsychological functions that are affected in ADHD. The goal is to familiarize the reader with the behavioral deficits that are hallmarks of ADHD and to facilitate comparisons with neurobehavioral deficits associated with environmental chemical exposures.
  
  
  METHODS
  Relevant literature on ADHD is reviewed, focusing in particular on meta-analyses conducted between 2004 and the present that evaluated associations between measures of neuropsychological function and ADHD in children. Meta-analyses were obtained through searches of the PubMed electronic database using the terms "ADHD," "meta-analysis," "attention," "executive," and "neuropsychological functions." Although meta-analyses are emphasized, nonquantitative reviews are included for particular neuropsychological functions where no meta-analyses were available.
  
  
  RESULTS
  The meta-analyses indicate that vigilance (sustained attention), response inhibition, and working memory are impaired in children diagnosed with ADHD. Similar but somewhat less consistent meta-analytic findings have been reported for impairments in alertness, cognitive flexibility, and planning. Additionally, the literature suggests deficits in temporal information processing and altered responses to reinforcement in children diagnosed with ADHD. Findings from brain imagining and neurochemistry studies support the behavioral findings.
  
  
  CONCLUSIONS
  Behavioral, neuroanatomical, and neurochemical data indicate substantial differences in attention and executive functions between children diagnosed with ADHD and non-ADHD controls. Comparisons of the neurobehavioral deficits associated with ADHD and those associated with exposures to environmental chemicals may help to identify possible environmental risk factors for ADHD and/or reveal common underlying biological mechanisms.
authors.affiliation: Department of Comparative Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802, USA. aaguiar@illinois.edu
authors.forename: Andréa
authors.initials: A
authors.lastname: Aguiar
authors.forename: Paul A
authors.initials: PA
authors.lastname: Eubig
authors.forename: Susan L
authors.initials: SL
authors.lastname: Schantz
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000139:chemically induced* / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology; D001921:Brain / Q000503:physiopathology; D002648:Child; D003071:Cognition; D039721:Diagnostic and Statistical Manual of Mental Disorders; D004782:Environmental Health; D004785:Environmental Pollutants / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D012307:Risk Factors
chemical_list: D004785:Environmental Pollutants