title: Beyond the dual pathway model: evidence for the dissociation of timing, inhibitory, and delay-related impairments in attention-deficit/hyperactivity disorder.
abstract: OBJECTIVE
  The dual pathway model explains neuro-psychological heterogeneity in Attention Deficit/Hyperactivity Disorder (ADHD) in terms of dissociable cognitive and motivational deficits each affecting some but not other patients. We explore whether deficits in temporal processing might constitute a third dissociable neuropsychological component of ADHD.
  
  
  METHODS
  Nine tasks designed to tap three domains (inhibitory control, delay aversion and temporal processing) were administered to ADHD probands (n=71; ages 6 to 17 years), their siblings (n=71; 65 unaffected by ADHD) and a group of non-ADHD controls (n=50). IQ and working memory were measured.
  
  
  RESULTS
  Temporal processing, inhibitory control and delay-related deficits represented independent neuropsychological components. ADHD children differed from controls on all factors. For ADHD patients, the co-occurrence of inhibitory, temporal processing and delay-related deficits was no greater than expected by chance with substantial groups of patients showing only one problem. Domain-specific patterns of familial co-segregation provided evidence for the validity of neuropsychological subgroupings.
  
  
  CONCLUSIONS
  The current results illustrate the neuropsychological heterogeneity in ADHD and initial support for a triple pathway model. The findings need to be replicated in larger samples.
authors.affiliation: Institute for Disorder of Impulse and Attention, School of Psychology, University of Southampton, Highfield, Southampton SO17 1BJ, UK. ejb3@soton.ac.uk
authors.forename: Edmund
authors.initials: E
authors.lastname: Sonuga-Barke
authors.forename: Paraskevi
authors.initials: P
authors.lastname: Bitsakou
authors.forename: Margaret
authors.initials: M
authors.lastname: Thompson
mesh_terms: D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology / Q000523:psychology; D002648:Child; D003071:Cognition; D006801:Humans; D007266:Inhibition, Psychological; D007361:Intelligence Tests; D008570:Memory, Short-Term; D008959:Models, Neurological; D008960:Models, Psychological; D009042:Motivation; D009483:Neuropsychological Tests; D009484:Neuropsychology; D035781:Siblings; D013998:Time Perception