title: Landmark recognition in Alzheimer's dementia: spared implicit memory for objects relevant for navigation.
abstract: BACKGROUND
  In spatial navigation, landmark recognition is crucial. Specifically, memory for objects placed at decision points on a route is relevant. Previous fMRI research in healthy adults showed higher medial-temporal lobe (MTL) activation for objects placed at decision points compared to non-decision points, even at an implicit level. Since there is evidence that implicit learning is intact in amnesic patients, the current study examined memory for objects relevant for navigation in patients with Alzheimer's dementia (AD).
  
  
  RESULTS
  21 AD patients participated with MTL atrophy assessed on MRI (mean MMSE = 21.2, SD = 4.0), as well as 20 age- and education-matched non-demented controls. All participants watched a 5-min video showing a route through a virtual museum with 20 objects placed at intersections (decision points) and 20 at simple turns (non-decision points). The instruction was to pay attention to the toys (half of the objects) for which they were supposedly tested later. Subsequently, a recognition test followed with the 40 previously presented objects among 40 distracter items (both toys and non-toys). Results showed a better performance for the non-toy objects placed at decision points than non-decision points, both for AD patients and controls.
  
  
  CONCLUSIONS
  Our findings indicate that AD patients with MTL damage have implicit memory for object information relevant for navigation. No decision point effect was found for the attended items. Possibly, focusing attention on the items occurred at the cost of the context information in AD, whereas the controls performed at an optimal level due to intact memory function.
authors.affiliation: Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands. r.kessels@donders.ru.nl
authors.forename: Roy P C
authors.initials: RP
authors.lastname: Kessels
authors.forename: Amy
authors.initials: A
authors.lastname: van Doormaal
authors.forename: Gabriele
authors.initials: G
authors.lastname: Janzen
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000503:physiopathology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D021641:Recognition, Psychology / Q000502:physiology*; D013037:Spatial Behavior / Q000502:physiology*