Declarative memory impairments in Alzheimer's disease and semantic dementia

Anatomical and functional alterations in semantic dementia: A voxel-based MRI and PET study

“…While episodic memory deficits could be partly due to semantic memory impairments, the use of a visual episodic task in our study suggests genuine episodic memory impairment, although definitely less serious than in Alzheimer Disease patients [52,58]. Finally, all the patients who underwent the behavioural assessment presented various changes, in line with growing evidence that many patients with SD have behavioural changes, sometimes identical to those suffering from the frontal variant of frontotemporal dementia [5,18,39,54,65,67].…”

“…Our findings regarding the hippocampus are in keeping with the study of Good et al [25] which used an optimized VBM procedure. The presence of significant atrophy in this region has also been reported in other studies using the ROI method [7,22,52]. In contrast with our findings, these latter authors showed that medial temporal lobe damage in SD was not associated with episodic memory deficits.…”

“…Both methods are observer-dependent and although the latter is quantitative, it only explores a selected set of structures on the basis of a priori hypotheses, potentially missing other areas. Only two PET studies of regional glucose metabolism used an objective and comprehensive voxel-based analysis, thanks to the SPM software [17,52] to assess hypometabolism in SD. Diehl et al [17] reported significant hypometabolism over the whole left temporal neocortex (excluding the hippocampus) and in the right temporal pole.…”

“…This phenomenon is particularly dramatic when cortical atrophy is present, such as in degenerative dementia. PVE correction has been applied in the recent study carried out by Nestor et al [52] who showed hypometabolism in bilateral temporal lobes, including the perirhinal cortex and extending to the fusiform gyrus.…”

“…Some authors [29,9] did not find significant atrophy of the hippocampus and adjacent structures using the SPM software which allows a voxel-by-voxel analysis (Voxel Based Morphometry, VBM) of the entire brain. Nevertheless, some studies using the region-of-interest (ROI) method [7,12,22,52] emphasized bilateral hippocampal atrophy, predominant on the left hemisphere. According to Chan et al [7] and Galton et al [22] the failure to identify hippocampal abnormality using VBM possibly reflects the limited resolution of the voxel-by-voxel method for small complex structures such as the hippocampus.…”