title: Altered brain response for semantic knowledge in Alzheimer's disease.
abstract: Word retrieval deficits are common in Alzheimer's disease (AD) and are thought to reflect a degradation of semantic memory. Yet, the nature of semantic deterioration in AD and the underlying neural correlates of these semantic memory changes remain largely unknown. We examined the semantic memory impairment in AD by investigating the neural correlates of category knowledge (e.g., living vs. nonliving) and featural processing (global vs. local visual information). During event-related fMRI, 10 adults diagnosed with mild AD and 22 cognitively normal (CN) older adults named aloud items from three categories for which processing of specific visual features has previously been dissociated from categorical features. Results showed widespread group differences in the categorical representation of semantic knowledge in several language-related brain areas. For example, the right inferior frontal gyrus showed selective brain response for nonliving items in the CN group but living items in the AD group. Additionally, the AD group showed increased brain response for word retrieval irrespective of category in Broca's homologue in the right hemisphere and rostral cingulate cortex bilaterally, which suggests greater recruitment of frontally mediated neural compensatory mechanisms in the face of semantic alteration.
authors.affiliation: Research Service, Veterans Affairs San Diego Healthcare System, San Diego, CA 92161, USA. cwierenga@ucsd.edu
authors.forename: Christina E
authors.initials: CE
authors.lastname: Wierenga
authors.forename: Nikki H
authors.initials: NH
authors.lastname: Stricker
authors.forename: Ashley
authors.initials: A
authors.lastname: McCauley
authors.forename: Alan
authors.initials: A
authors.lastname: Simmons
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Jak
authors.forename: Yu-Ling
authors.initials: YL
authors.lastname: Chang
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Nation
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Bangen
authors.forename: David P
authors.initials: DP
authors.lastname: Salmon
authors.forename: Mark W
authors.initials: MW
authors.lastname: Bondi
mesh_terms: D000368:Aged; D000544:Alzheimer Disease / Q000503:physiopathology / Q000523:psychology*; D001921:Brain / Q000503:physiopathology*; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D019359:Knowledge; D007802:Language; D008279:Magnetic Resonance Imaging; D008297:Male; D008569:Memory Disorders / Q000503:physiopathology / Q000523:psychology; D011939:Mental Recall / Q000502:physiology; D009483:Neuropsychological Tests; D010100:Oxygen / Q000097:blood; D017397:Prefrontal Cortex / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology; D012660:Semantics; D012959:Socioeconomic Factors; D014796:Visual Perception / Q000502:physiology
chemical_list: D010100:Oxygen