3D Shape Perception in Posterior Cortical Atrophy: A Visual Neuroscience Perspective

Abstract

Posterior cortical atrophy (PCA) is a rare focal neurodegenerative syndrome characterized by progressive visuoperceptual and visuospatial deficits, most often due to atypical Alzheimer's disease (AD). We applied insights from basic visual neuroscience to analyze 3D shape perception in humans affected by PCA. Thirteen PCA patients and 30 matched healthy controls participated, together with two patient control groups with diffuse Lewy body dementia (DLBD) and an amnestic-dominant phenotype of AD, respectively. The hierarchical study design consisted of 3D shape processing for 4 cues (shading, motion, texture, and binocular disparity) with corresponding 2D and elementary feature extraction control conditions. PCA and DLBD exhibited severe 3D shape-processing deficits and AD to a lesser degree. In PCA, deficient 3D shape-from-shading was associated with volume loss in the right posterior inferior temporal cortex. This region coincided with a region of functional activation during 3D shape-from-shading in healthy controls. In PCA patients who performed the same fMRI paradigm, response amplitude during 3D shape-from-shading was reduced in this region. Gray matter volume in this region also correlated with 3D shape-from-shading in AD. 3D shape-from-disparity in PCA was associated with volume loss slightly more anteriorly in posterior inferior temporal cortex as well as in ventral premotor cortex. The findings in right posterior inferior temporal cortex and right premotor cortex are consistent with neurophysiologically based models of the functional anatomy of 3D shape processing. However, in DLBD, 3D shape deficits rely on mechanisms distinct from inferior temporal structural integrity. Key words: Alzheimer's disease; depth perception; fMRI; Lewy body; voxel-based morphometry Significance StatementPosterior cortical atrophy (PCA) is a neurodegenerative syndrome characterized by progressive visuoperceptual dysfunction and most often an atypical presentation of Alzheimer's disease (AD) affecting the ventral and dorsal visual streams rather than the medial temporal system. We applied insights from fundamental visual neuroscience to analyze 3D shape perception in PCA. 3D shape-processing deficits were affected beyond what could be accounted for by lower-order processing deficits. For shading and disparity, this was related to volume loss in regions previously implicated in 3D shape processing in the intact human and nonhuman primate brain. Typical amnestic-dominant AD patients also exhibited 3D shape deficits. Advanced visual neuroscience provides insight into the pathogenesis of PCA that also bears relevance for vision in typical AD.

Tau PET imaging predicts cognition in atypical variants of Alzheimer's disease

“…The visuospatial eigenvector explained 85% of the variance in cognitive scores and was localized to right lingual gyrus, where both PCA and aAD patients had elevated uptake. Although this result suggests that tau accumulation in early visual areas may be a good predictor of visuospatial impairment, it does not imply that pathology in these regions alone accounts for patients' deficits; indeed, PCA patients often have impairments that suggest complex interactions of disease in the ventral and dorsal visual streams (e.g., Gillebert et al, ; Meek, Shelton, and Marotta, ), and PCA is associated with ventral and dorsal stream structural changes that can occur either in isolation or concurrently within an individual patient (Migliaccio et al, ). Moreover, recent consensus criteria for PCA diagnosis allow for subtypes of this syndrome that differ in the lateralization of disease (Crutch et al, ).…”

Cholinergic depletion and basal forebrain volume in primary progressive aphasia

“…Preprocessing of the T 1 -weighted images was performed with Voxel-Based Morphometry 8 (VBM8) (Ashburner and Friston, 2000), implemented in Matlab R2012b as described previously (Gillebert et al, 2015). This procedure generated non-linear only modulated GM maps, corrected for total intracranial volumetric differences.…”

Microstructural properties of the vertical occipital fasciculus explain the variability in human stereoacuity

“…This asymmetry is consistent with previous studies that report the lateralization of disparity processing to the right hemisphere. For example, neuropsychological studies have reported that brain damage causing the loss of stereoscopic depth perception is lateralized to the right hemisphere (18,64,(72)(73)(74)(75)(76)(77). Furthermore, fMRI studies have demonstrated some evidence for the lateralization of the cortical response to disparity-defined stimuli to the right hemisphere (41,43,(78)(79)(80).…”