title: fMRI guided rTMS evidence for reduced left prefrontal involvement after task practice.
abstract: BACKGROUND
  Cognitive tasks that do not change the required response for a stimulus over time ('consistent mapping') show dramatically improved performance after relative short periods of practice. This improvement is associated with reduced brain activity in a large network of brain regions, including left prefrontal and parietal cortex. The present study used fMRI-guided repetitive transcranial magnetic stimulation (rTMS), which has been shown to reduce processing efficacy, to examine if the reduced activity in these regions also reflects reduced involvement, or possibly increased efficiency.
  
  
  METHODS
  First, subjects performed runs of a Sternberg task in the scanner with novel or practiced target-sets. This data was used to identify individual sites for left prefrontal and parietal peak brain activity, as well as to examine the change in activity related to practice. Outside of the scanner, real and sham rTMS was applied at left prefrontal and parietal cortex to examine their involvement novel and practiced conditions.
  
  
  RESULTS
  Prefrontal as well as parietal rTMS significantly reduced target accuracy for novel targets. Prefrontal, but not parietal, rTMS interference was significantly lower for practiced than novel target-sets. rTMS did not affect non-target accuracy, or reaction time in any condition.
  
  
  CONCLUSIONS
  These results show that task practice in a consistent environment reduces involvement of the prefrontal cortex. Our findings suggest that prefrontal cortex is predominantly involved in target maintenance and comparison, as rTMS interference was only detectable for targets. Findings support process switching hypotheses that propose that practice creates the possibility to select a response without the need to compare with target items. Our results also support the notion that practice allows for redistribution of limited maintenance resources.
authors.affiliation: Department of Neurology and Neurosurgery, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Johan Martijn
authors.initials: JM
authors.lastname: Jansma
authors.affiliation: Department of Neurology and Neurosurgery, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands ; Department of Child- and Adolescent Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Tamar R
authors.initials: TR
authors.lastname: van Raalten
authors.affiliation: Department of Neurology and Neurosurgery, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Ruud
authors.initials: R
authors.lastname: Boessen
authors.affiliation: Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Sebastiaan F W
authors.initials: SF
authors.lastname: Neggers
authors.affiliation: Department of Neurology and Neurosurgery, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Richard H A H
authors.initials: RH
authors.lastname: Jacobs
authors.affiliation: Department of Psychiatry, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: René S
authors.initials: RS
authors.lastname: Kahn
authors.affiliation: Department of Neurology and Neurosurgery, Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Nick F
authors.initials: NF
authors.lastname: Ramsey
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D017397:Prefrontal Cortex / Q000502:physiology*; D011930:Reaction Time; D012815:Signal Processing, Computer-Assisted; D013647:Task Performance and Analysis; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult