FDG-PET mapping the brain substrates of visuo-constructive processing in Alzheimeŕs disease

Department of Nuclear Medicine, Ludwig-Maximilian University, Munich, Germany.
Journal of Psychiatric Research (Impact Factor: 3.96). 10/2009; 44(7):462-9. DOI: 10.1016/j.jpsychires.2009.09.012
Source: PubMed


The anatomical basis of visuo-constructive impairment in AD is widely unexplored. FDG-PET can be used to determine functional neuronal networks underlying specific cognitive performance in the human brain. In the present study, we determined the pattern of cortical metabolism that was associated with visuo-constructive performance in AD. We employed two widely used visuo-constructive tests that differ in their demand on visual perception and processing capacity. Resting state FDG-PET scans were obtained in 29 probable AD patients, and cognitive tests were administered. We made a voxel-based regression analysis of FDG uptake to scores in visual test performance, using the SPM5 software. Performance in the CERAD Drawing test correlated with FDG uptake in the bilateral inferior temporal gyri, bilateral precuneus, right cuneus, right supramarginal gyrus and right middle temporal gyrus covering areas of dorsal and ventral visual streams. In contrast, performance in the more complex RBANS Figure Copy test correlated with FDG uptake in the bilateral fusiform gyri, right inferior temporal gyrus, left anterior cingulate gyrus, left parahippocampal gyrus, right middle temporal gyrus and right insula, encompassing the ventral visual stream and areas of higher-level visual processing. The study revealed neuronal networks underlying impaired visual test performance in AD. The extent of involvement of visual and higher order association cortex increased with greater test complexity. From a clinical point of view, both of these widely used visual tests evaluate the integrity of complementary cortical networks and may contribute complementary information on the integrity of visual processing in AD.

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    • "The dorsal stream, including the precuneus (BA7) and the middle temporal gyrus (BA21), is also known as the " where/how pathway " , and it is implicated in spatial localization of objects and shape [54]. The atrophy we detected in all these cortical areas of ADca patients is likely to be crucial for their characteristic symptoms, as also suggested by a previous FDG-PET study [55]. "
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    ABSTRACT: Constructional apraxia (CA) is often, but not always, observed in patients with Alzheimer's disease (AD). CA is usually explained by impairment of either basic perceptual and motor abilities, or of executive functions. This study aims to evaluate the structural correlates of CA in AD. Forty-eight patients with AD and 20 healthy age-matched controls underwent a thorough neuropsychological investigation and an MRI scan to collect high-resolution T1-weighted data. Patients were classified as having (ADca) or not having (ADnonca) CA based on performance on the Freehand copying of drawings task. T1-weighted volumes were processed according the voxel-based morphometry protocol, to assess the presence of significant differences in local grey matter volume in patients compared to controls and in ADca compared to ADnonca. Post-hoc, the mean grey matter volume of clusters that resulted significantly different between groups was regressed against the neuropsychological scores in which the two patient groups performed differently. A pre-senile disease onset was significantly more frequent in patients with CA compared to ADnonca. ADca patients also showed worse performances than patients with ADnonca at some tests requiring the processing of visuo-spatial data and testing working memory. They also showed widespread reductions in grey matter volume, mainly located in areas known to be implicated in object recognition and localization, and in maintenance and re-orienting of spatial attention. These findings suggest that the occurrence of CA in AD is often associated with a peculiar clinical onset (i.e., pre-senile), neuropsychological profile, and distribution of grey matter atrophy.
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    • "The RBANS has also been reported to be predictive of functional capacity (i.e., driving) in patients with MCI (Badenes Guia, Casas Hernanz, Cejudo Bolivar, & Aguilar Barbera, 2008). The RBANS correlates with all six domains of the Clinical Dementia Rating Scale in patients with MCI and AD (Hobson, Hall, Humphreys-Clark, Schrimsher, & O'Bryant, 2010), and the RBANS has been shown to correlate with AD biomarkers, including functional neuroimaging data in patients with AD (Forster et al., 2010; Wilson et al., 2009). Finally, the RBANS has been shown to be sensitive to detecting cognitive enhancement in computer training designed to boost memory functioning in non-demented older adults (Mahncke et al., 2006) and in a small clinical trial in MCI (Kotani et al., 2006). "
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    • "The right hemisphere is known to be mainly involved in visuospatial ability and attention, musical, and emotional functions (Joseph, 1988), whereas the left hemisphere is deemed to be predominantly associated with language and its related semantic knowledge processing (Geschwind and Galaburda, 1985; Foxe et al., 2003; Caplan, 2006; Bartolomeo et al., 2012). Especially, the right inferior temporal gyrus (BA 20) has been implicated in cortical processing of complex visual objects including face or clock (Forster et al., 2010), and the right inferior parietal regions including the supramarginal (BA 40) and angular gyri (BA 39) are vital for good visuoconstructive performance (Villa et al., 1986). Patients with lesions in the right BA 39/40 usually very poorly copy and depict the size, shape, proportions, and relationships of visual percepts (Caplan, 2006). "
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