Brain perfusion correlates of visuoperceptual deficits in mild cognitive impairment and mild Alzheimer's disease

Abstract

Visuoperceptual processing is impaired early in the clinical course of Alzheimer's disease (AD). The 15-Objects Test (15-OT) detects such subtle performance deficits in mild cognitive impairment (MCI) and mild AD. Reduced brain perfusion in the temporal, parietal, and prefrontal regions have been found in early AD and MCI patients. The objectives of this study were to confirm the role of the 15-OT in the diagnosis of MCI and AD and to investigate the brain perfusion correlates of visuoperceptual dysfunction (15-OT) in subjects with MCI, AD, and normal aging. Forty-two AD, 42 MCI, and 42 healthy elderly control subjects underwent a brain Single Photon Emission Tomography (SPECT) and separately completed the 15-OT. An analysis of variance compared 15-OT scores between groups. SPM5 was used to analyse the SPECT data. 15-OT performance was impaired in the MCI and AD patients. In terms of the SPECT scans, AD patients showed reduced perfusion in temporal-parietal regions, while the MCI subjects had decreased perfusion in the middle and posterior cingulate. When MCI and AD groups were compared, a significant brain perfusion reduction was found in temporo-parietal regions. In the whole sample, 15-OT performance was significantly correlated with the clinical dementia rating scores, and with the perfusion in the bilateral posterior cingulate and the right temporal pole, with no significant correlation in each separate group. Our findings suggest that the 15-OT performance provides a useful gradation of impairment from normal aging to AD, and it seems to be related to perfusion in the bilateral posterior cingulate and the right temporal pole.

Figure 1

The section rendering of the contrast between the EC and AD groups (SPECT images) projected onto the T1 template image from SPM5. The areas marked in yellow have significantly higher flow in the EC group compared to the AD patients (FDR= 0.05, extent threshold 100 voxels).

Figure 2

The mean and standard deviations of the eigenvariates derived from the SPM5 analysis. The values were taken at the peak voxel, with an area including a sphere of 1 voxel radius. The standard deviation was taken from the MANCOVA (controlling for age) and is group-specific. The differences between all of the groups were significant in each of the five brain regions (p< 0.001).

Figure 3

Scatterplots of performance on the MMSE (left panel) and the 15-OT (right panel) as a function of the eigenvariate from the posterior cingulate gyrus region of interest. Each point represents a single subject in each group, and the lines represent the best-fit regression lines for each group. The green lines represent the EC group, the orange the MCI, and the red AD.