Semantic memory deficits in low-educated patients with Alzheimer's disease.
OBJECTIVE
Although a deficit of semantic memory is evident in the dementia of the Alzheimer's type (DAT), the underlying neuropsychologic mechanism remains controversial. Breakdown of the semantic network during the course of DAT and an inability to access semantic information have been postulated as possible explanations, but supporting data are limited, particularly in low-educated patients. This study examined semantic memory in low-educated patients with different degrees of dementia severity.


METHODS
In total, 197 adult subjects were recruited, including 165 DAT patients and 32 normal controls. Subjects were divided into four subgroups according to their dementia severity. All subjects completed an episodic memory task, the Six-Object Memory Test, and semantic memory tasks including the Object Naming Test, the Remote Memory Test and the Semantic Association of Verbal Fluency Test. One-way ANOVA and ANCOVA with a post hoc Scheffe's procedure were used to evaluate differences between groups.


RESULTS
All patients, irrespective of the degree of dementia, showed impaired performance on the Six-Object Memory Test [F (4, 163) = 69.95, p < 0.0001 for immediate recall; F (4, 163) = 41.34, p < 0.0001 for delayed recall]. On the semantic memory tasks, patients with moderate to severe dementia showed impaired performances on the Object Naming Test [F (4, 180) = 28.25, p < 0.0001] and the Remote Memory Test [F (4, 167) = 26.22, p < 0.0001 for recall; F (4, 167) = 34.80, p < 0.0001 for recognition], while all patients performed defectively on the Semantic Association of Verbal Fluency Test [F (4, 194) = 70.43, p < 0.0001].


CONCLUSIONS
Our results thus partially support the hypotheses that a loss of semantic structure and an inability to access semantic knowledge occur in the pathogenesis of DAT.
Yang
Chi-Cheng
CC
Department of Psychology, National Taiwan University, Taipei, Taiwan.
Hua
Mau-Sun
MS
Chiu
Ming-Jang
MJ
Chen
Sien-Tsong
ST
Yip
Ping-Keung
PK
Chen
Ta-Fu
TF
Wu
Chih-Hsun
CH
Wen
Ming-Ching
MC
Tseng
Huai-Hsuan
HH
Chu
Yi-Chuan
YC
D000368:Aged; D016022:Case-Control Studies; D003704:Dementia / Q000503:physiopathology*; D004522:Educational Status; D006801:Humans; D011939:Mental Recall / Q000502:physiology*; D009483:Neuropsychological Tests; D012660:Semantics; D012720:Severity of Illness Index