Distinct neuroanatomical bases of episodic and semantic memory performance in Alzheimer’s disease

• Published in: Neuropsychologia 2013-04, Vol.51 (5), p.930-937
• Main Authors: Hirni, Daniela I., Kivisaari, Sasa L., Monsch, Andreas U., Taylor, Kirsten I.
• Format: Article
• Language: English
• Subjects: Adult and adolescent clinical studies; Aged; Aged, 80 and over; Alzheimer Disease - complications; Alzheimer Disease - pathology; Alzheimer Disease - psychology; Alzheimer’s disease; Analysis of Variance; Anisotropy; Biological and medical sciences; Brain - pathology; Cognitive Dysfunction - pathology; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Diffusion Magnetic Resonance Imaging; Entorhinal cortex; Episodic memory; Female; Hippocampus; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Male; Medical sciences; Memory Disorders - etiology; Memory, Episodic; Neurology; Neuropsychological Tests; Organic mental disorders. Neuropsychology; Perirhinal cortex; Psychology. Psychoanalysis. Psychiatry; Psychopathology. Psychiatry; Semantic memory; Semantics
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/j.neuropsychologia.2013.01.013

Alzheimer’s disease (AD) neurofibrillary pathology begins in the medial perirhinal cortex (mPRC) before spreading to the entorhinal cortex (ERC) and hippocampus (HP) in anterior medial temporal lobe (aMTL). While the role of the ERC/HP complex in episodic memory formation is well-established, recent research suggests that the PRC is required to form semantic memories of individual objects. We aimed to test whether commonly used clinical measures of episodic and semantic memory are distinctly associated with ERC/HP and mPRC integrity, respectively, in healthy mature individuals and very early AD patients. One hundred thirty normal controls, 32 amnestic mild cognitive impairment patients, some of whom are in the earliest (i.e., preclinical) stages of AD, and ten early-stage AD patients received neuropsychological testing and high-resolution anatomic and diffusion MRI. Voxel-based regression analyses tested for regions where episodic memory (delayed recall scores on the California Verbal Learning and Rey Osterrieth Complex Figure Tests) and semantic memory (Boston Naming Test, category fluency) performance correlated with gray matter (GM) regions of interest and whole-brain fractional anisotropy (FA) voxel values. When controlling for the opposing memory performance, poorer episodic memory performance was associated with reduced bilateral ERC/HP GM volume and related white matter integrity, but not with mPRC GM volume. Poor semantic memory performance was associated with both reduced left mPRC and ERC/HP GM volume, as well as reduced FA values in white matter tracts leading to the PRC. These results indicate a partial division of labor within the aMTL and suggest that mPRC damage in very early AD may be detectable with common clinical tests of semantic memory if episodic memory performance is controlled. ► We assessed the functional specialization of episodic and semantic memory. ► Participants were healthy or had very early Alzheimer’s disease. ► Regressions with gray matter and FA controlled for contrasting memory performance. ► Episodic memory correlated with entorhinal cortex, hippocampal integrity. ► Semantic memory performance correlated with perirhinal cortex integrity.