Abstract
BackgroundIn 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).Methodology/Principal Findings21 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.Conclusion/SignificanceOur 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.
Highlights
For successful navigation in our environment, information about landmarks, spatial locations and routes has to be efficiently processed
Conclusion/Significance: Our findings indicate that Alzheimer’s dementia (AD) patients with medial-temporal lobe (MTL) damage have implicit memory for object information relevant for navigation
Non-toys placed at decision points significantly differ from toys at decision points for AD patients but not for the controls (t(19) = 2.5, p,0.05)
Summary
For successful navigation in our environment, information about landmarks, spatial locations and routes has to be efficiently processed. Functional neuroimaging studies in healthy volunteers have demonstrated increased parahippocampal activation related to memory for objects relevant for navigation, i.e. landmarks at decision points, compared to objects that are irrelevant for navigation (objects placed at non-decision points). This latter finding was reported for landmark objects that were not correctly recognized in a later object recognition task, indicating that object information that is relevant for navigation may be processed in an automatic way [6,7,8]. 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)
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