Journal
NEUROIMAGE
Volume 30, Issue 3, Pages 1010-1020Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.neuroimage.2005.10.008
Keywords
Alzheimer's disease; semantic dementia; episodic memory; semantic memory; PET
Funding
- Medical Research Council [G108/653, MC_U105559861, G9724461] Funding Source: researchfish
- MRC [G9724461, MC_U105559861, G108/653] Funding Source: UKRI
- Medical Research Council [G108/653, G9724461, MC_U105559861] Funding Source: Medline
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Semantic dementia (SD) and Alzheimer's disease (AD) are both disorders in which early pathology affects the temporal lobe Net they produce distinct syndromes of declarative memory impairment-loss of established semantic knowledge with relatively preserved episodic memory in the former and the converse in the latter. Groups with mild SD and mild AD who showed a double dissociation in these two aspects of declarative memory were studied-the SD group's episodic memory and the AD group's semantic knowledge each being comparable to controls. Positron emission tomography and volumetric magnetic resonance imaging were used to map deficits in regional cerebral metabolic rate and mesial temporal lobe MTL atrophy, respectively. Episodic memory impairment in AD was associated with dysfunction of an integrated network (mesial temporal lobe, mamillary bodies, dorsomesial thalamus and posterior cingulate). Semantic memory impairment in SD was associated with bilateral rostra] temporal lobe hypometabolism. The SD group had comparable MTL atrophy and hypometabolism to that found in AD but the remainder of their limbic-diencephalic network was preserved suggesting that the latter explains their ability to acquire new episodic memories. The results challenge the view that amnesia in early AD can be explained by the degree of MTL damage alone while showing that semantic impairment can occur with damage restricted to the rostral temporal lobes. (c) 2005 Elsevier Inc. All rights reserved.
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