title: Examining dorsal striatum in cognitive effort using Parkinson's disease and fMRI.
abstract: OBJECTIVE
  Understanding cognition mediated by the striatum can clarify cognitive deficits in Parkinson's disease (PD). Previously, we claimed that dorsal striatum (DS) mediates cognitive flexibility. To refute the possibility that variation in cognitive effort confounded our observations, we reexamined our data to dissociate cognitive flexibility from effort. PD provides a model for exploring DS-mediated functions. In PD, dopamine-producing cells supplying DS are significantly degenerated. DS-mediated functions are impaired off and improved on dopamine replacement medication. Functional magnetic resonance imaging (fMRI) can confirm striatum-mediated functions.
  
  
  METHODS
  Twenty-two PD patients, off-on dopaminergic medication, and 22 healthy age-matched controls performed a number selection task. Numerical distance between number pairs varied systematically. Selecting between two numbers that are closer versus distant in magnitude is more effortful: the symbolic distance effect. However, selecting between closer versus distant number pairs is equivalent in the need to alter attention or response strategies (i.e., cognitive flexibility). In Experiment 2, 28 healthy participants performed the same task with simultaneous measurement of brain activity with fMRI.
  
  
  RESULTS
  The symbolic distance effect was equivalent for PD versus control participants and across medication sessions. Furthermore, symbolic distance did not correlate with DS activation using fMRI. In this dataset, we showed previously that integrating conflicting influences on decision making is (1) impaired in PD and improved by dopaminergic therapy and (2) associated with preferential DS activation using fMRI.
  
  
  CONCLUSIONS
  These findings support the notion that DS mediates cognitive flexibility specifically, not merely cognitive effort, accounting for some cognitive deficits in PD and informing treatment.
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada.
authors.forename: Alex A
authors.initials: AA
authors.lastname: MacDonald
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada.
authors.forename: Ken N
authors.initials: KN
authors.lastname: Seergobin
authors.affiliation: Faculty of Law, University of Ottawa Ottawa, Ontario, Canada.
authors.forename: Ruzbeh
authors.initials: R
authors.lastname: Tamjeedi
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada ; Department of Psychology, University of Western Ontario London, Ontario, Canada.
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Owen
authors.affiliation: Functional Neuroimaging Unit, Centre de Recherche, Institut Universitaire de Gériatrie de Montréal Montréal, Québec, Canada ; Department of Radiology, University of Montréal Montréal, Québec, Canada.
authors.forename: Jean-Sebastien
authors.initials: JS
authors.lastname: Provost
authors.affiliation: Functional Neuroimaging Unit, Centre de Recherche, Institut Universitaire de Gériatrie de Montréal Montréal, Québec, Canada ; Department of Radiology, University of Montréal Montréal, Québec, Canada.
authors.forename: Oury
authors.initials: O
authors.lastname: Monchi
authors.affiliation: Department of Psychiatry, University of Western Ontario London, Ontario, Canada.
authors.forename: Hooman
authors.initials: H
authors.lastname: Ganjavi
authors.affiliation: Brain and Mind Institute, University of Western Ontario London, Ontario, Canada ; Department of Clinical Neurological Sciences, University of Western Ontario London, Ontario, Canada.
authors.forename: Penny A
authors.initials: PA
authors.lastname: MacDonald