title: Extinction learning deficit in a rodent model of attention-deficit hyperactivity disorder.
abstract: BACKGROUND
  Deficient operant extinction has been hypothesized to be constitutive of ADHD dysfunction. In order to elucidate the behavioral mechanisms underlying this deficit, the performance of an animal model of ADHD, the spontaneously hypertensive rat (SHR), was compared against the performance of a control strain, the Wistar-Kyoto rat (WKY) during extinction.
  
  
  METHODS
  Following extensive training of lever pressing under variable interval schedules of food reinforcement (reported previously), SHR and WKY rats were exposed to two sessions of extinction training. Extinction data was analyzed using the Dynamic Bi-Exponential Refractory Model (DBERM) of operant performance. DBERM assumes that operant responses are organized in bouts separated by pauses; during extinction, bouts may decline across multiple dimensions, including frequency and length. DBERM parameters were estimated using hierarchical Bayesian modeling.
  
  
  RESULTS
  SHR responded more than WKY during the first extinction session. DBERM parameter estimates revealed that, at the onset of extinction, SHR produced more response bouts than WKY. Over the course of extinction, response bouts progressively shortened for WKY but not for SHR.
  
  
  CONCLUSIONS
  Based on prior findings on the sensitivity of DBERM parameters to motivational and schedule manipulations, present data suggests that (1) more frequent response bouts in SHR are likely related to greater incentive motivation, and (2) the persistent length of bouts in SHR are likely related to a slower updating of the response-outcome association. Overall, these findings suggest specific motivational and learning deficits that may explain ADHD-related impairments in operant performance.
authors.affiliation: Arizona State University, PO Box 871104, Tempe, AZ 85287-1104, USA. ryan.brackney@asu.edu
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Brackney
authors.forename: Timothy H C
authors.initials: TH
authors.lastname: Cheung
authors.forename: Katrina
authors.initials: K
authors.lastname: Herbst
authors.forename: Jade C
authors.initials: JC
authors.lastname: Hill
authors.forename: Federico
authors.initials: F
authors.lastname: Sanabria
mesh_terms: D000818:Animals; D001288:Attention / Q000502:physiology*; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology / Q000523:psychology*; D001522:Behavior, Animal / Q000502:physiology; D003216:Conditioning, Operant / Q000502:physiology*; D004195:Disease Models, Animal; D005108:Extinction, Psychological / Q000502:physiology*; D008297:Male; D009042:Motivation / Q000502:physiology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012055:Reinforcement Schedule; D013045:Species Specificity