Word-stem completion task to investigate semantic network in patients with Alzheimer's disease

Repetition Priming in Individuals with Amnestic Mild Cognitive Impairment and Alzheimer's Dementia: a Systematic Review and Meta-Analysis

The literature on repetition priming in Alzheimer's disease (AD) is inconsistent, with some findings supporting spared priming while others do not. Several factors may explain these inconsistencies, including AD severity (e.g., dementia vs. Mild Cognitive Impairment; MCI) and priming paradigm-related characteristics. This systematic review and meta-analysis provides a quantitative summary of repetition priming in AD. We examined the between-group standard mean difference comparing repetition priming in AD dementia or amnestic MCI (aMCI; presumably due to AD) to controls. Thirty-two studies were selected, including 590 individuals with AD dementia, 267 individuals with amnestic MCI, and 703 controls. Our results indicated that both individuals with aMCI and AD dementia perform worse on repetition priming tasks than cognitively older adults. Paradigm-related moderators suggested that the effect size between studies comparing the combined aMCI or AD dementia group to cognitively healthy older adults was the highest for paradigms that required participants to produce, rather than identify, primes during the test phase. Our results further suggested that priming in AD is impaired for both conceptual and perceptual priming tasks. Lastly, while our results suggested that priming in AD is impaired for priming tasks that require deep processing, we were unable to draw firm conclusions about whether priming is less impaired in aMCI or AD dementia for paradigms that require shallow processing.

Word Processing Is Faster than Picture Processing in Alzheimer's Disease

Objective

Alzheimer's disease (AD) is characterized by a slow progressive impairment of episodic memory. Many studies have shown that AD exhibits deterioration of semantic memory during the course of disease progression. We previously reported that AD patients exhibited severe access disorders in the semantic memory system, using the Momentary Presentation Task (20 or 300 ms). In this study, we studied access disorder in patients with AD by the use of object difference (pictures vs words) methods.

Methods

56 patients with probable AD (NINCDS-ADRDA, mean age 79.0 years) and 11 healthy controls (HC) (mean age 67.0 years) were studied. Ten pictures and 10 corresponding Japanese Hiragana words were presented arbitrarily for 20 and 300 ms on the monitor screen which were correctly named at the usual confrontation setting (i.e., semantic memory preserved). They were asked to name the pictures or to read the words or nonsense syllables aloud.

Results

The AD group showed significantly lower scores than the HC group, especially for the 20 ms condition. For the type of stimuli, the AD patients had better performances for words > pictures > nonsense syllables, although no differences for the HC group. The effect of AD severity was noted, moderate > severe stage.

Conclusions

Our results suggested that the processing speed in AD patients may have reduced, even if the semantic memory were preserved. These data indicated that the difference in the processing speeds by the type of stimuli (pictures, words, and nonsense syllables) may be a character of AD patients.

Lexical Priming in Alzheimer's Disease and Aphasia

Lexical priming was examined in patients with Alzheimer's disease and in aphasic patients. Control participants were divided into young and elderly [cf. Arroyo-Anlló et al.: Eur J Cogn Psychol 2004;16:535-553]. For lexical priming, a word-stem completion task was used. Normal elderly participants had lexical priming scores that were significantly lower than those of young individuals. Analysis of covariance with age and educational level as covariates showed that the control participants, aphasic and Alzheimer patients did not differ significantly on the lexical priming task. Our results suggest that performance in the lexical priming task diminishes with physiological aging, but is not significantly affected by mild or moderate Alzheimer's disease or by fluent or non-fluent aphasia.

The loss of conceptual associations in mild Alzheimer's dementia

Changes in semantic memory are a controversial topic in research on cognitive decline in aging. In this study, we analyzed whether the semantic deficits in mild Alzheimer's disease (AD) reflect the information acquisition process, and whether the deficits are related to when the information was initially stored. We hypothesized that in the earlier stages of dementia, the ability to access semantic associative relations reflects the use of these associations during different developmental stages. Specifically, we asserted that Alzheimer's patients might be able to access the relations that are learned earlier in life for the longest amount of time compared to those that are learned later. In this study, 254 subjects were divided into four groups (child, adult, senior, and Alzheimer's patients groups) and were evaluated with an experimental semantic association task that incorporated five semantic associative relations that were used to compare performance by age group. An analysis of variance (ANOVA) 4 × 5 test showed a significant main group effect, F(3, 250) = 97.1, p < .001, and an associative relations effect, F(4, 1000) = 23.1, p < .001, as well as an interaction of Group × Associative Relations, F(12, 1000) = 8.5, p < .001. The results demonstrated that the semantic associative relations that were acquired in later developmental stages were less preserved in persons with mild AD (i.e., superordinate relation, p < .0001). On the contrary, the semantic relations acquired earlier in childhood were better preserved in persons with mild AD. Our results suggest that semantic impairment begins with difficulties in using the associative relations that link concepts together in the semantic memory of patients with mild AD dementia (and possibly in individuals with mild cognitive impairment).

The minute hand phenomenon in the Clock Test of patients with early Alzheimer disease

Common scoring systems for the Clock Test do not sufficiently emphasize the correct time representation by the clock hands. We compared Clock Drawing, Clock Setting, and Clock Reading in healthy control persons, patients with mild cognitive impairment, early Alzheimer disease and progressed Alzheimer disease particularly analyzing clock time representation. We found that healthy control persons and participants with mild cognitive impairment did not show any impairment in Clock Test performance. Patients with early Alzheimer disease could be discriminated from healthy control persons and participants with mild cognitive impairment solely by misplacement of the minute hand in Clock Drawing and Clock Setting. The progressed Alzheimer disease group showed significantly more impairments in all Clock Test variants. It is assumed that early stage Alzheimer disease patient deficits in Clock Tests are mainly determined by a reduced access to semantic memory about the appearance and functionality of a clock.