title: Dopaminergic therapy affects learning and impulsivity in Parkinson's disease.
abstract: OBJECTIVE
  The aim was to examine the effect of dopaminergic medication on stimulus-response learning versus performing decisions based on learning.
  
  
  METHODS
  To see the effect of dopaminergic therapy on stimulus-response learning and response selection, participants with Parkinson's disease (PD) were either tested on and/or off their prescribed dose of dopaminergic therapy during different testing days. Forty participants with PD and 34 healthy controls completed the experiment on consecutive days. On Day 1, participants learned to associate abstract images with spoken, "right" or "left" responses via feedback (Session 1). On Day 2, participants recalled these responses (Session 2) and indicated the location (i.e., right or left of center) of previously studied images intermixed with new images (Session 3).
  
  
  RESULTS
  Participants with PD off medication learned stimulus-response associations equally well compared to healthy controls. Learning was impaired by dopaminergic medication. Regardless of medication status, patients recalled the stimulus-response associations from Day 1 as well as controls. In Session 3 off medication, patients demonstrated enhanced facilitation relative to controls and patients on medication, when the stimulus location was congruent with the spoken response that was learned for the stimulus in Session 1.
  
  
  CONCLUSIONS
  Learning in PD was comparable to that of healthy controls off medication. Learning was worsened by dopaminergic therapy in PD. We interpret greater facilitation in participants with PD off medication for congruent responses as evidence of greater impulsivity. This motor or reflexive impulsivity was normalized by medication in PD. These findings shed light on the cognitive profile of PD and have implications for dopaminergic treatment.
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada, N6A 5B7 ; Department of Physiology and Pharmacology, University of Western Ontario London, Ontario, Canada, N6A 5C1.
authors.forename: Nole M
authors.initials: NM
authors.lastname: Hiebert
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada, N6A 5B7.
authors.forename: Ken N
authors.initials: KN
authors.lastname: Seergobin
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada, N6A 5B7 ; Department of Psychology, University of Western Ontario London, Ontario, Canada, N6A 5C2.
authors.forename: Andrew
authors.initials: A
authors.lastname: Vo
authors.affiliation: Department of Psychiatry, University of Western Ontario London, Ontario, Canada, N6A 5W9.
authors.forename: Hooman
authors.initials: H
authors.lastname: Ganjavi
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada, N6A 5B7 ; Department of Physiology and Pharmacology, University of Western Ontario London, Ontario, Canada, N6A 5C1 ; Department of Psychology, University of Western Ontario London, Ontario, Canada, N6A 5C2 ; Department of Clinical Neurological Sciences, University of Western Ontario London, Ontario, Canada, N6A 5A5.
authors.forename: Penny A
authors.initials: PA
authors.lastname: MacDonald