Abstract
The location and motion of sounds in space are important cues for encoding the auditory world. Spatial processing is a core component of auditory scene analysis, a cognitively demanding function that is vulnerable in Alzheimer's disease. Here we designed a novel neuropsychological battery based on a virtual space paradigm to assess auditory spatial processing in patient cohorts with clinically typical Alzheimer's disease (n = 20) and its major variant syndrome, posterior cortical atrophy (n = 12) in relation to healthy older controls (n = 26). We assessed three dimensions of auditory spatial function: externalized versus non-externalized sound discrimination, moving versus stationary sound discrimination and stationary auditory spatial position discrimination, together with non-spatial auditory and visual spatial control tasks. Neuroanatomical correlates of auditory spatial processing were assessed using voxel-based morphometry. Relative to healthy older controls, both patient groups exhibited impairments in detection of auditory motion, and stationary sound position discrimination. The posterior cortical atrophy group showed greater impairment for auditory motion processing and the processing of a non-spatial control complex auditory property (timbre) than the typical Alzheimer's disease group. Voxel-based morphometry in the patient cohort revealed grey matter correlates of auditory motion detection and spatial position discrimination in right inferior parietal cortex and precuneus, respectively. These findings delineate auditory spatial processing deficits in typical and posterior Alzheimer's disease phenotypes that are related to posterior cortical regions involved in both syndromic variants and modulated by the syndromic profile of brain degeneration. Auditory spatial deficits contribute to impaired spatial awareness in Alzheimer's disease and may constitute a novel perceptual model for probing brain network disintegration across the Alzheimer's disease syndromic spectrum.
Highlights
Sound is a major source of information from the world around us, where vision is unavailable or reduced
Whereas the typical Alzheimer’s disease and healthy control groups were well matched for age, the posterior cortical atrophy (PCA) group was on average significantly younger than both the control group [beta = 6.18, 95% confidence interval (CI) 4.5 to 7.8, P 5 0.001] and the typical Alzheimer’s disease group [beta = 5.67, CI 3.9 to 7.4, P 5 0.001]
We have shown that clinically typical amnestic Alzheimer’s disease and PCA are both associated with impaired auditory spatial processing
Summary
Sound is a major source of information from the world around us, where vision is unavailable or reduced. Auditory scene analysis and localization of sounds in space entail formidable computational problems (Bregman, 1990): these are solved efficiently and automatically by the normal brain but potentially significant in brain disorders associated with reduced spatial acuity, such as Alzheimer’s disease. The clinical and Received May 23, 2014.
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