Episodic and semantic memory tasks activate different brain regions in Alzheimer disease

• Published in: Neurology Vol. 65; no. 2; p. 266
• Main Authors: Starr, J M, Loeffler, B, Abousleiman, Y, Simonotto, E, Marshall, I, Goddard, N, Wardlaw, J M
• Format: Journal Article
• Language: English
• Published: United States 26.07.2005
• Subjects: Adaptation, Physiological - physiology; Aged; Aged, 80 and over; Alzheimer Disease - pathology; Alzheimer Disease - physiopathology; Alzheimer Disease - psychology; Brain - pathology; Brain - physiology; Brain - physiopathology; Female; Functional Laterality - physiology; Gyrus Cinguli - pathology; Gyrus Cinguli - physiology; Gyrus Cinguli - physiopathology; Humans; Male; Memory - physiology; Memory, Short-Term - physiology; Nerve Net - pathology; Nerve Net - physiology; Nerve Net - physiopathology; Neural Pathways - pathology; Neural Pathways - physiology; Neural Pathways - physiopathology; Neuronal Plasticity - physiology; Neuropsychological Tests; Parahippocampal Gyrus - pathology; Parahippocampal Gyrus - physiology; Parahippocampal Gyrus - physiopathology; Prefrontal Cortex - pathology; Prefrontal Cortex - physiology; Prefrontal Cortex - physiopathology
• ISSN: 1526-632X
• DOI: 10.1212/01.wnl.0000168907.44632.55

To compare brain activity identified by fMRI in subjects with Alzheimer disease (AD) and older healthy controls (HCs) performing an episodic/working memory (EWM) and semantic memory (SM) task. Nine AD (mean age 73.6) and 10 HC (mean age 71.8) subjects underwent an fMRI memory paradigm. Tasks comprised 1) baseline (recognizing a single digit presented for 1 second), 2) SM (addition of two single digits, always producing a single digit answer), and 3) EWM (recall of the previous single digit on the stimulus of the next digit). Each condition was presented in 2-minute blocks with a shorter and longer time interval for the first and second minute within blocks. Comparing AD and HC subjects, there were no activated brain regions in common for EWM > SM, but left anterior cingulate (Brodmann area [BA] 24, 0, 31, 4) and left medial frontal lobe gyrus (BA 25, -6, 23, -15) were activated by both groups for SM > EWM. Key differences were that for EWM > SM, HC subjects activated the right parahippocampal gyrus, whereas subjects with AD activated the right superior frontal gyrus and left uncus. Subjects with Alzheimer disease (AD) recruited brain regions for easier episodic/working memory (EWM) tasks used by healthy controls (HCs) for more difficult EWM tasks. AD subjects recruited brain regions for semantic memory tasks used by HCs for more difficult EWM tasks. The authors propose a functional "memory reserve" model of compensatory recruitment according to task difficulty and underlying neuropathology.