title: Changes in cortical activation during retrieval of clock time representations in patients with mild cognitive impairment and early Alzheimer's disease.
abstract: OBJECTIVE
  We investigated healthy controls (HCs), and patients with mild cognitive impairment (MCI) and early Alzheimer's disease (AD) to identify neuronal correlates of clock time representation and changes resulting from neurodegenerative processes using functional magnetic resonance imaging.
  
  
  METHODS
  Two clock-specific tasks demanding conceptual knowledge of clock hands, i.e. a minute hand and an hour hand task, were compared with a semantic control task.
  
  
  RESULTS
  We observed that the minute hand task provoked a stronger activation of areas in the parietal lobes known to be involved in spatial mental imagery, while the semantic task primarily activated regions of the superior temporal lobes associated with verbal conceptual knowledge. The performance of the MCI group did not differ from that of the HC group, but additional activation was found in several brain regions. Decreased activation was detected during the minute hand task in the right middle temporal gyrus. Patients with early AD showed deteriorated performance in both clock tasks along with reduced activation in the occipital lobes and the left fusiform gyrus. Additional activation was detected in the precuneus.
  
  
  CONCLUSIONS
  The fusiform gyrus might be crucial for the visual-semantic retrieval of clock time representation. In patients with early AD, access to this visual-semantic knowledge appears to be reduced.
authors.affiliation: Department of Psychiatry and Psychotherapy, University of Tübingen, Tübingen, Germany. thomas.leyhe@med.uni-tuebingen.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Leyhe
authors.forename: Michael
authors.initials: M
authors.lastname: Erb
authors.forename: Monika
authors.initials: M
authors.lastname: Milian
authors.forename: Gerhard W
authors.initials: GW
authors.lastname: Eschweiler
authors.forename: Thomas
authors.initials: T
authors.lastname: Ethofer
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Grodd
authors.forename: Ralf
authors.initials: R
authors.lastname: Saur
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000503:physiopathology / Q000523:psychology*; D000704:Analysis of Variance; D002540:Cerebral Cortex / Q000503:physiopathology*; D003072:Cognition Disorders / Q000503:physiopathology / Q000523:psychology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D009415:Nerve Net / Q000503:physiopathology; D009483:Neuropsychological Tests; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology