Alzheimer’s disease as a window to neural mechanisms of cognition

Two articles in this issue of Neurology focus on neuropsychological studies in Alzheimer’s disease (AD). Using voxel-based MRI morphometry, Boxer et al.1 report a strong association between impaired copying performance on a modified version of the Rey–Osterrieth figure and gray matter loss in the right inferior temporal gyrus in AD. Monacelli et al.2 report a novel test of visuospatial learning in which subjects traverse a route through a complex environment. They find that a tendency to become lost is most strongly predicted by failure on a test of route learning that requires subjects to recall the visuospatial configurations at turning points and to place them in a mental map of the route. Both studies exemplify the use of AD as a lesion model to better understand the neural basis of cognitive function. Although somewhat cumbersome, the highly original test developed by Monacelli et al. holds promise as a sensitive early clinical marker of AD.

By testing the ability of their subjects to copy a modified version of the Rey–Osterrieth figure, Boxer et al. probed the function of the “what” visual pathway in a topographic domain (stimulus elements related to each other in terms of spatial configuration rather than sequence), thereby engaging the “what” pathway in the right hemisphere.3 Consequently, their findings are logical. Moreover, they have provided empirical validation that has not been possible with other lesion models. Patients with right hemisphere (middle cerebral artery distribution) strokes commonly demonstrate constructional apraxia characterized by detailed but disorganized drawings that often fail to capture the gestalt of the target.4 However, …