title: Intraindividual variability in inhibitory function in adults with ADHD--an ex-Gaussian approach.
abstract: OBJECTIVE
  Attention deficit disorder (ADHD) is commonly associated with inhibitory dysfunction contributing to typical behavioral symptoms like impulsivity or hyperactivity. However, some studies analyzing intraindividual variability (IIV) of reaction times in children with ADHD (cADHD) question a predominance of inhibitory deficits. IIV is a measure of the stability of information processing and provides evidence that longer reaction times (RT) in inhibitory tasks in cADHD are due to only a few prolonged responses which may indicate deficits in sustained attention rather than inhibitory dysfunction. We wanted to find out, whether a slowing in inhibitory functioning in adults with ADHD (aADHD) is due to isolated slow responses.
  
  
  METHODS
  Computing classical RT measures (mean RT, SD), ex-Gaussian parameters of IIV (which allow a better separation of reaction time (mu), variability (sigma) and abnormally slow responses (tau) than classical measures) as well as errors of omission and commission, we examined response inhibition in a well-established GoNogo task in a sample of aADHD subjects without medication and healthy controls matched for age, gender and education.
  
  
  RESULTS
  We did not find higher numbers of commission errors in aADHD, while the number of omissions was significantly increased compared with controls. In contrast to increased mean RT, the distributional parameter mu did not document a significant slowing in aADHD. However, subjects with aADHD were characterized by increased IIV throughout the entire RT distribution as indicated by the parameters sigma and tau as well as the SD of reaction time. Moreover, we found a significant correlation between tau and the number of omission errors.
  
  
  CONCLUSIONS
  Our findings question a primacy of inhibitory deficits in aADHD and provide evidence for attentional dysfunction. The present findings may have theoretical implications for etiological models of ADHD as well as more practical implications for neuropsychological testing in aADHD.
authors.affiliation: Department of Clinical Psychology and Neuropsychology, SRH Klinikum, Karlsbad-Langensteinbach, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Gmehlin
authors.affiliation: Department of Clinical and Developmental Neuropsychology, University of Groningen, Groningen, The Netherlands.
authors.forename: Anselm B M
authors.initials: AB
authors.lastname: Fuermaier
authors.affiliation: Section of Experimental Psychopathology and Neurophysiology, Department of child and adolescent Psychiatry, University of Heidelberg, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Walther
authors.affiliation: Schuhfried GmbH, Mödling, Austria.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Debelak
authors.affiliation: Department of Clinical Psychology and Neuropsychology, SRH Klinikum, Karlsbad-Langensteinbach, Germany.
authors.forename: Mirjam
authors.initials: M
authors.lastname: Rentrop
authors.affiliation: Department of Clinical Psychology and Neuropsychology, SRH Klinikum, Karlsbad-Langensteinbach, Germany.
authors.forename: Celina
authors.initials: C
authors.lastname: Westermann
authors.affiliation: Section of Experimental Psychopathology and Neurophysiology, Department of child and adolescent Psychiatry, University of Heidelberg, Germany.
authors.forename: Anuradha
authors.initials: A
authors.lastname: Sharma
authors.affiliation: Department of Clinical and Developmental Neuropsychology, University of Groningen, Groningen, The Netherlands.
authors.forename: Lara
authors.initials: L
authors.lastname: Tucha
authors.affiliation: Department of Clinical and Developmental Neuropsychology, University of Groningen, Groningen, The Netherlands.
authors.forename: Janneke
authors.initials: J
authors.lastname: Koerts
authors.affiliation: Department of Clinical and Developmental Neuropsychology, University of Groningen, Groningen, The Netherlands.
authors.forename: Oliver
authors.initials: O
authors.lastname: Tucha
authors.affiliation: Psychiatric Department, SRH Klinikum, Karlsbad-Langensteinbach, Germany; SüdWestAkadamie für Neuropsychologie (SWAN), Heidelberg, Germany; Section of Experimental Psychopathology and Neurophysiology, Department of child and adolescent Psychiatry, University of Heidelberg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Weisbrod
authors.affiliation: Department of Clinical Psychology and Neuropsychology, SRH Klinikum, Karlsbad-Langensteinbach, Germany; SüdWestAkadamie für Neuropsychologie (SWAN), Heidelberg, Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Aschenbrenner
mesh_terms: D000328:Adult; D000368:Aged; D001288:Attention / Q000502:physiology; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology*; D002755:Choice Behavior / Q000502:physiology; D005260:Female; D006801:Humans; D006948:Hyperkinesis / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D009484:Neuropsychology; D016011:Normal Distribution; D011930:Reaction Time / Q000502:physiology*