Semantic memory in Alzheimer's disease

Patients with Alzheimer's disease have been suggested to have a semantic memory impairment not present in the normal old. This article reviews the performance of Alzheimer patients on tests of various aspects of semantic memory, including word finding, knowledge of the semantic attributes, and associates of concepts, as well as their category membership. The effect that semantic context has on cognitive processes such as lexical and semantic priming and memory encoding is also reviewed. Finally, the ability of theoretical constructs such as implicit memory and automaticity to explain intertask variability in Alzheimer patients' semantic performance is discussed.     

Priming and semantic memory loss in Alzheimer's disease

Semantic memory (SM) was investigated in six patients with probable Alzheimer's disease (AD) by on-line measurement of semantic priming in a lexical decision task, and off-line tests of comprehension. Detailed assessment was carried out on naming, name comprehension, and probes of semantic knowledge with a battery of 150 items. The patients performed normally on perceptual tests and displayed an item-specific loss of knowledge on the semantic tests. In a primed lexical decision task, greater semantic priming was found relative to age-matched normals. The priming was substantially greater for items with "degraded" representations as determined by the off-line tests. Lexical decision was also performed more slowly on these items. These unexpected results demand a reevaluation of the concepts of the lexicon and semantic memory structure and their possible alteration in dementia.     

Directed forgetting of autobiographical memory in mild Alzheimer's disease

Using the autobiographical directed forgetting method (Barnier et al., 2007), the present paper addressed the intentional inhibitory processes of episodic and semantic autobiographical memory in Alzheimer's disease (AD). Mild AD patients and healthy elderly people were instructed to either forget or to continue remembering previously generated autobiographical events. In a later recall test they were asked to reconstruct the early-generated memories regardless of the forget/remember instruction. Autobiographical reconstruction was further distributed into episodic and semantic memories. Results showed no forget instruction effect on episodic or semantic autobiographical recall with AD patients, whereas healthy elderly people were able to inhibit only episodic autobiographical memories. The findings suggest an impairment of the intentional inhibitory processes in autobiographical memory with AD and a relative preservation of these mechanisms with normal ageing. They also demonstrate an earlier decline in the intentional inhibitory processes compared to the autobiographical deterioration in AD.     

Categories, prototypes and memory systems in Alzheimer's disease

Recent studies indicate that category learning is mediated by multiple neuronal systems. It has been shown that patients with marked impairments in executive functions, explicit memory and procedural learning can categorize the exemplars and prototype of a previously trained category. Simple, self-organizing neuronal networks can explain prototype learning and related dysfunctions in Alzheimer's disease, and provide a model of how prototype learning is mediated by circumscribed mechanisms in the visual cortex.     

The deterioration of semantic memory in Alzheimer's disease.

Semantic memory impairment is a common feature of dementia of the Alzheimer type (DAT). Recent research has shown that patients with DAT are more impaired (relative to non-demented controls) in generating exemplars from a particular semantic category (e.g., animals) than words beginning with a particular letter, exhibit an altered temporal dynamic during the production of category exemplars, are impaired on confrontation naming tasks and make predominantly superordinate or semantically related errors, consistently misidentify the same objects across a variety of semantic tasks, and have alterations in multi-dimensional scaling models of their semantic network that are indicative of a loss of concepts and associations. These results are consistent with the view that Alzheimer's disease results in a breakdown in the organization and structure of semantic knowledge as neurodegeneration spreads to the association cortices that presumably store semantic representations.     

Modeling recall memory for emotional objects in Alzheimer's disease

ABSTRACT

Objective: To examine whether emotional memory (EM) of objects with self-reference in Alzheimer's disease (AD) can be modeled with binomial logistic regression in a free recall and an object recognition test to predict EM enhancement.?Method: Twenty patients with AD and twenty healthy controls were studied. Six objects (three presented as gifts) were shown to each participant. Ten minutes later, a free recall and a recognition test were applied. The recognition test had target–objects mixed with six similar distracter objects. Participants were asked to name any object in the recall test and identify each object in the recognition test as known or unknown.?Results: The total of gift objects recalled in AD patients (41.6%) was larger than neutral objects (13.3%) and a significant EM recall effect for gifts was found (Wilcoxon: p < .003). EM was not found for recognition in AD patients due to a ceiling effect. Healthy older adults scored overall higher in recall and recognition but showed no EM enhancement due to a ceiling effect. A logistic regression showed that likelihood of emotional recall memory can be modeled as a function of MMSE score (p < .014) and object status (p < .0001) as gift or non-gift.?Conclusion: Recall memory was enhanced in AD patients for emotional objects indicating that EM in mild to moderate AD although impaired can be provoked with strong emotional load. The logistic regression model suggests that EM declines with the progression of AD rather than disrupts and may be a useful tool for evaluating magnitude of emotional load.     

Directed forgetting of autobiographical memory in mild Alzheimer's disease

Using the autobiographical directed forgetting method (Barnier et al., 2007), the present paper addressed the intentional inhibitory processes of episodic and semantic autobiographical memory in Alzheimer's disease (AD). Mild AD patients and healthy elderly people were instructed to either forget or to continue remembering previously generated autobiographical events. In a later recall test they were asked to reconstruct the early-generated memories regardless of the forget/remember instruction. Autobiographical reconstruction was further distributed into episodic and semantic memories. Results showed no forget instruction effect on episodic or semantic autobiographical recall with AD patients, whereas healthy elderly people were able to inhibit only episodic autobiographical memories. The findings suggest an impairment of the intentional inhibitory processes in autobiographical memory with AD and a relative preservation of these mechanisms with normal ageing. They also demonstrate an earlier decline in the intentional inhibitory processes compared to the autobiographical deterioration in AD.     

Pattern of semantic memory impairment in dementia of Alzheimer's type

The specific pattern of semantic memory impairment in patients with dementia of Alzheimer's type (DAT) remains unclear. Specifically, the presence of a category-specific deficit for biological concepts (reflected in anomia for these concepts) has been questioned. We studied 9 DAT patients using a semantic association judgement test in which they had to decide which of the two given words was most like a target word (e.g., lamb: goat, sheep). The 150 target words were drawn from 6 categories: animals, clothing and furniture, fruits and vegetables, tools, action verbs, and abstract nouns. Age- and education-matched control subjects performed equivalently (between 86 and 90% correct) in all categories. Compared to control subjects, DAT patients made significantly more errors in abstract and biological nouns, but not in verbs and man-made artifacts. This pattern of semantic memory impairment--a sparing of verbs and a selective deficit of nouns in the biological category--has been documented in patients with temporal lobe damage, suggesting a critical dysfunction in the temporal lobes of DAT.     

Effects of normal aging and Alzheimer's disease on emotional memory

Recall is typically better for emotional than for neutral stimuli. This enhancement is believed to rely on limbic regions. Memory is also better for neutral stimuli embedded in an emotional context. The neural substrate supporting this effect has not been thoroughly investigated but may include frontal lobe, as well as limbic circuits. Alzheimer's disease (AD) results in atrophy of limbic structures, whereas normal aging relatively spares limbic regions but affects prefrontal areas. The authors hypothesized that AD would reduce all enhancement effects, whereas aging would disproportionately affect enhancement based on emotional context. The results confirmed the authors' hypotheses: Young and older adults, but not AD patients, showed better memory for emotional versus neutral pictures and words. Older adults and AD patients showed no benefit from emotional context, whereas young adults remembered more items embedded in an emotional versus neutral context.     

Assessing working memory and language comprehension in Alzheimer's disease.

Studies of language impairments in patients with Alzheimer's disease have often assumed that impairments in linguistic working memory underlie comprehension deficits. Assessment of this hypothesis has been hindered both by vagueness of key terms such as "working memory" and by limitations of available working memory tasks, in that many such tasks either seem to have little relationship to language comprehension or are too confusing or difficult for Alzheimer's patients. Four experiments investigated the usefulness of digit ordering, a new task assessing linguistic working memory and/or language processing skill, in normal adults and patients with probable Alzheimer's disease. The digit ordering task was shown to be strongly correlated with the degree of dementia in Alzheimer's patients. The task correlated with measures of language processing on which patients and normal controls performed differently. The results are interpreted as indicating that linguistic representations, linguistic processing, and linguistic working memory are intertwined, such that a deficit of one (e.g., working memory) cannot be said to "cause" a deficit in the other. The implications of this approach are explored in terms of task demands in comprehension and memory measures, and interpretation of previous results in the literature.     

Short- and long-term implicit memory in aging and Alzheimer's disease

Implicit memory processes were investigated via picture naming in healthy young and older adults and in persons with mild Alzheimer's disease (AD). Repetition priming in picture-naming was intact in all groups over the course of a short retention interval (seconds), and only the AD group revealed a deficit over a longer interval (72 hours). In addition, the AD group showed impaired procedural memory, with no benefit of practice on picture-naming. Impaired long-term priming was related to severity of AD. Both theoretical and methodological implications are discussed.     

Memory of myself: autobiographical memory and identity in Alzheimer's disease

A number of theories posit a relationship between autobiographical memory and identity. To test this we assessed the status of autobiographical memory and identity in 20 individuals with Alzheimer's disease (AD) and 20 age-matched controls, and investigated whether degree of autobiographical memory impairment was associated with changes in identity. Two tests of autobiographical memory (Autobiographical Memory Interview, autobiographical fluency) and two measures of identity (Twenty Statements Test, identity items of the Tennessee Self Concept Scale) were administered. AD participants exhibited significant impairments on both memory tests, and changes in the strength, quality, and direction of identity relative to controls. Impairments of some components of autobiographical memory, particularly autobiographical memory for childhood and early adulthood, were related to changes in the strength and quality of identity. These findings support the critical role of early adulthood autobiographical memories (16-25 years) in identity, and suggest autobiographical memory loss affects identity.     

Memory of myself: Autobiographical memory and identity in Alzheimer's disease

A number of theories posit a relationship between autobiographical memory and identity. To test this we assessed the status of autobiographical memory and identity in 20 individuals with Alzheimer's disease (AD) and 20 age‐matched controls, and investigated whether degree of autobiographical memory impairment was associated with changes in identity. Two tests of autobiographical memory (Autobiographical Memory Interview, autobiographical fluency) and two measures of identity (Twenty Statements Test, identity items of the Tennessee Self Concept Scale) were administered. AD participants exhibited significant impairments on both memory tests, and changes in the strength, quality, and direction of identity relative to controls. Impairments of some components of autobiographical memory, particularly autobiographical memory for childhood and early adulthood, were related to changes in the strength and quality of identity. These findings support the critical role of early adulthood autobiographical memories (16–25 years) in identity, and suggest autobiographical memory loss affects identity.     

Episodic and semantic memory influences on picture naming in Alzheimer's disease

This study investigated the relationship between semantic and episodic memory as they support lexical access by healthy younger and older adults and individuals with Alzheimer's disease (AD). In particular, we were interested in examining the pattern of semantic and episodic memory declines in AD (i.e., word-finding difficulty and impaired recent memory) vis-à-vis more preserved remote memories. We administered a picture naming task in which the episodic period of the pictures and whether the pictured items were unique to one period or commonly used across periods were varied. Groups of younger adults (N=40), healthy older adults (N=20) and older adults with AD (N=18) were asked to name drawings of objects in four conditions: dated unique, contemporary unique, dated common, and contemporary common. The results indicated that all participants named items that were common to both episodic periods more successfully than items unique to one period. An interaction was observed such that the healthy older and AD groups were more successful in retrieving names of objects presented in the dated compared to contemporary unique conditions, whereas the younger adults showed the reverse pattern. These results indicate that naming ability is affected both by the cumulative frequency of using an item over a lifetime and by when an item was first acquired. The findings support a theoretical stance which proposes an enduring reciprocal link between semantic and episodic memory. This theoretical relationship has practical implications for the development of intervention strategies when interacting with persons who have AD.     

Evaluation of prospective memory training for individuals with mild Alzheimer's disease

Prospective memory (PM) refers to the timely execution of a previously formed intention. PM deficits are one of the earliest measurable deficits in Alzheimer's disease (AD; Huppert & Beardsall, 1993) and yet, there has been little systematic research devoted to identifying ways in which these deficits can be compensated for or minimized. In this pilot study, individuals with mild AD participated in a new training program aimed at improving PM performance on an experimental PM task. PM training consisted of errorless learning and spaced retrieval techniques taught in six sessions in subjects' homes. Results showed that compared to untrained AD controls. AD patients who received PM training performed a PM task successfully across 7 weeks posttreatment (over 90% accuracy; controls 16-33% accuracy).     

Differential memory impairment in dementia with Lewy bodies and Alzheimer's disease

This study was conducted in order to elucidate the functioning of the Central Executive System of Working Memory (WM) and to clarify the status of other cognitive functions in Dementia with Lewy bodies (DLB) and Alzheimer's disease (AD). Fourteen DLB, 22 AD, and 23 control subjects were assessed with the dual task paradigm and other cognitive tests. When compared with controls, DLB subjects performed more poorly in concurrent conditions on semantic WM tasks, and AD subjects performed more poorly on the spatial WM task. The DLB subjects had an inferior verbal span and AD subjects, an inferior recall on the CVLT. These data suggest relative impairments of verbal and semantic WM in DLB and relative impairments of spatial WM and verbal episodic memory in AD.     

The role of histone acetylation in age-associated memory impairment and Alzheimer's disease

Learning and memory are cognitive processes that are tightly regulated. A proper genome-environment interaction is a pre-requisite for cognitive function. Epigenetic processes are central regulators of genome-environment interactions. In line with this, it has been shown that the epigenetic machinery is essential for cognitive function. With a specific focus on histone acetylation, we will discuss recent research in the field of epigenetic mechanisms of learning and memory. We will also specifically address the role of histone acetylation in age-associated memory impairment and Alzheimer's disease and ask the question why targeting the epigenome could be a suitable strategy for neuroprotection and neuroregeneration.