Early Detection of Semantic Memory Changes May Help Predict the
Course of Alzheimer’s Disease
Hsin Te Chang1, Ming-Jang Chiu2and Mau Sun Hua1,3*
1Department of Psychology, College of Medical and Health Science, Asia University, Taichung, Taiwan
2Department of Neurology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan
3Department of Psychology, College of Science, National Taiwan University, Taipei, Taiwan
- *Corresponding Author:
- MauSun Hua
Department of Psychology
Science, National Taiwan University
No.1, Sec. 4, Roosevelt Road
Tel: +886 2 33663101
E-mail: [email protected]
Received date: May 26, 2017; Accepted date: June 02, 2017; Published date: June 09, 2017
Citation: Chang HT, Chiu MJ, Hua MS (2017) Early Detection of Semantic Memory Changes May Help Predict the Course of Alzheimer’s Disease. J Alzheimers Dis
Parkinsonism 7:333. doi:10.4172/2161-0460.1000333
Copyright: © 2017 Chang HT, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Visit for more related articles at Journal of Alzheimers Disease & Parkinsonism
Over the course of Alzheimer’s disease (AD), patients suffer from
relentless progressive dementia. Characterization of at-risk stages of AD
is crucial for targeted prevention of dementia . Neuropathological evidence suggests that earliest AD affects declarative memory [2-
4], which can be further categorized as either episodic memory or
semantic memory [5,6]. Episodic memory deals with specific events
of the past, whereas semantic memory deals with general knowledge
of the world [6,7]. The earliest neuropathological changes in patients
with AD may correlate more strongly with semantic memory than
episodic memory [2,8,9]. Therefore, detecting early changes in the
semantic memory of AD patients may be clinically important. Semantic
memory impairment has been well-documented among patients with
dementia of the Alzheimer type (DAT) [10-19] and among patients
with prodromal stage of DAT (amnestic mild cognitive impairment,
aMCI) [20-29]. Semantic memory deficits may occur early in the
disease course of AD and therefore comprise useful markers of disease
progression. However, the predictive value of semantic memory
impairment remains controversial [20,22,27,29]. The previously
observed inconsistencies may be attributable to distinct processes of
semantic memory retrieval [10,30]. Many complex mental operations
associated with semantic memory retrieval can be performed with
minimal attentional capacity by dint of extensive practice. These types
of mental operations are considered ‘automatic’. Conversely, other tasks
that involve semantic memory retrieval require considerable attentional
capacity to perform and are commonly referred to as ‘effortful’. AD
patients display disproportionally poor performance on semantic
tasks that require the effortful retrieval of semantic memories, whereas
automatic retrieval tends to be better preserved . Chang et al. .
Compared effortful and automatic retrieval of semantic memory among
individuals with aMCI , DAT or subjective memory impairment
(SMI) . In this study, patients with DAT and aMCI-multiple domain
(aMCI-md)  displayed poor performance on all semantic memory
tasks. Conversely, patients with aMCI-single domain (aMCI-sd) 
were found to have performed more poorly on a semantic memory task
that required a relatively high degree of effortful retrieval. In addition,
the risk of conversion from MCI to DAT (approximately 27 months
after the first evaluation) among aMCI-sd patients who displayed
poor performance on semantic memory tasks requiring effortful
retrieval exceeded the risk faced by aMCI-sd patients who performed
normally on the same tasks by more than two-fold in this study (50%
vs. 23%). In contrast, aMCI-md patients who presented poor semantic
memory in tasks that required automatic retrieval were at higher risk
of conversion to DAT (58% vs. 38%). Nonetheless, the sensitivity of
performance on the semantic memory task requiring high degree of
effortful retrieval in predicting conversion from aMCI to DAT was
relatively low compared to specificity in this study. Recent studies have
suggested that combining performance on semantic memory tasks with
biomarkers of AD may facilitate the prediction [22,28,33]. In addition,
novel neurophysiological markers have been proposed by researchers
to detect early neuropathological changes in AD and other cognitive disorders (e.g. increased excitability of motor cortex in transcranial
magnetic stimulation studies [34-38]). The relatively low sensitivity of semantic memory performance in predicting DAT conversion among
aMCI patients in Chang et al.  may be due to that the study did
not incorporate the biomarkers of AD in the prediction. Moreover,
combining other tasks requiring effortful semantic memory retrieval
may also improve the sensitivity in predicting DAT conversion among
aMCI patients [39-41].
Overall, neuropathological evidence has revealed that the
deterioration of semantic memory generally occurs earlier than the
deterioration of episodic memory in the disease course of AD. The
controlled processes involved in semantic memory retrieval may
provide cognitive markers for the characterization and prediction of
neuropathological changes among patients in the prodromal stage AD.
We suggest that future researchers perform a large-scale longitudinal
study incorporating biomarkers to address various aspects of semantic
memory retrieval that characterize the early disease stages of AD (e.g.
SMI). Such a study should help to more fully elucidate the value of
semantic memory in predicting the conversion of MCI to DAT.
This study was supported by a grant from the Ministry of Science and
Technology, Taipei, Taiwan (NSC 102-2410-H-002-051-MY3). The authors have
no disclosures to report.
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