Mohamad El Haj

Autobiographical memory decline in Alzheimer's disease, a theoretical and clinical overview.

Autobiographical memory, or memory for personal experiences, allows individuals to define themselves and construct a meaningful life story. Decline of this ability, as observed in Alzheimers disease (AD), results in an impaired sense of self and identity. In our model (AMAD: Autobiographical Memory in Alzheimers Disease), we present a critical review of theories and findings regarding cognitive and neuroanatomical underpinnings of autobiographical memory and its decline in AD and highlight studies on its clinical rehabilitation. We propose that autobiographical recall in AD is mainly characterized by loss of associated episodic information, which leads to de-contextualization of autobiographical memories and a shift from reliving past events to a general sense of familiarity. This decline refers to retrograde, but also anterograde amnesia that affects newly acquired memories besides remote ones. One consequence of autobiographical memory decline in AD is decreased access to memories that shape self-consciousness, self-knowledge, and self-images, leading to a diminished sense of self and identity. The link between autobiographical decline and compromised sense of self in AD can also manifest itself as low correspondence and coherence between past memories and current goals and beliefs. By linking cognitive, neuroanatomical, and clinical aspects of autobiographical decline in AD, our review provides a theoretical foundation, which may lead to better rehabilitation strategies.

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 Alzheimers 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.

Flexibility decline contributes to similarity of past and future thinking in Alzheimer's disease

A striking similarity has been suggested between past and future thinking in Alzheimers Disease (AD), a similarity attributable to abnormalities in common modular cognitive functions and neuroanatomical substrates. This study extends this literature by identifying specific executive function deficits underlying past and future thinking in AD. Twenty‐four participants with a clinical diagnosis of probable (mild) AD and 26 older controls generated past and future events and underwent tests of binding and the executive functions of flexibility, inhibition, and updating. AD patients showed similar autobiographical performances in past and future event generation, and so did control participants. In each group, the similarity of past and future thinking was predicted by flexibility. Furthermore, AD patients with low flexibility showed higher similarity of past and future thinking than those with high flexibility. These findings are interpreted in terms of involvement of the hippocampus and frontal lobes in future thinking. Deficits in these brain regions in AD are likely to compromise the ability to recombine episodic information into novel and flexible configurations as scenarios for the future.

To what extent does destination recall induce episodic reliving? Evidence from Alzheimer's disease.

We compared destination memory to source memory in patients with Alzheimer’s disease (AD), as the latter type of memory is believed to be severely deteriorated in AD. Control participants and AD patients were tested on two conditions, both of which had a study phase and a recognition phase. In the study phase of the first condition, participants had to tell a set of facts to the faces of a set of celebrities (destination memory). In the study phase of the second condition, they had to receive a different set of facts from a different set of celebrity faces (source memory). During the recognition phase, participants had to indicate, for destination memory, whether they had previously told a given fact to a given face (yes) or not (no) and, for source memory, whether they had previously received a given fact from a given face (yes) or not (no). In both conditions, they were asked to choose between “remember” or “know” options when answering “yes.” AD patients showed reliable difficulties in destination recall, accompanied by a significant decrease in the number of “remember” responses they gave. AD-related destination memory decline may be attributed to the perturbation of episodic memory and its autonoetic reliving. The potential neural bases of this decline are discussed in terms of hippocampal failures.

Prospective and retrospective time perception are related to mental time travel: evidence from Alzheimer's disease.

Unlike prospective time perception paradigms, in which participants are aware that they have to estimate forthcoming time, little is known about retrospective time perception in normal aging and Alzheimers disease (AD). Our paper addresses this shortcoming by comparing prospective and retrospective time estimation in younger adults, older adults, and AD patients. In four prospective tasks (lasting 30s, 60s, 90s, or 120s) participants were asked to read a series of numbers and to provide a verbal estimation of the reading time. In four other retrospective tasks, they were not informed about time judgment until they were asked to provide a verbal estimation of four elapsed time intervals (lasting 30s, 60s, 90s, or 120s). AD participants gave shorter verbal time estimations than older adults and younger participants did, suggesting that time is perceived to pass quickly in these patients. For all participants, the duration of the retrospective tasks was underestimated as compared to the prospective tasks and both estimations were shorter than the real time interval. Prospective time estimation was further correlated with mental time travel, as measured with the Remember/Know paradigm. Mental time travel was even higher correlated with retrospective time estimation. Our findings shed light on the relationship between time perception and the ability to mentally project oneself into time, two skills contributing to human memory functioning. Finally, time perception deficits, as observed in AD patients, can be interpreted in terms of dramatic changes occurring in frontal lobes and hippocampus.

Self-defining memories during exposure to music in Alzheimer's disease

BACKGROUND Research suggests that exposure to music may enhance autobiographical recall in Alzheimers Disease (AD) patients. This study investigated whether exposure to music could enhance the production of self-defining memories, that is, memories that contribute to self-discovery, self-understanding, and identity in AD patients. METHODS Twenty-two mild-stage AD patients and 24 healthy controls were asked to produce autobiographical memories in silence, while listening to researcher-chosen music, and to their own-chosen music. RESULTS AD patients showed better autobiographical recall when listening to their own-chosen music than to researcher-chosen music or than in silence. More precisely, they produced more self-defining memories during exposure to their own-chosen music than to researcher-chosen music or during silence. Additionally, AD patients produced more self-defining memories than autobiographical episodes or personal-semantics during exposure to their own-chosen music. This pattern contrasted with the poor production of self-defining memories during silence or during exposure to researcher-chosen music. Healthy controls did not seem to enjoy the same autobiographical benefits nor the same self-defining memory enhancement in the self-chosen music condition. CONCLUSIONS Poor production of self-defining memories, as observed in AD, may somehow be alleviated by exposure to self-chosen music.

What do we know about the relationship between source monitoring deficits and executive dysfunction

In clinical neuropsychology, source monitoring deficits have been classically attributed to executive dysfunction. Nevertheless, in this review we identified only 16 papers that provided statistical data about the relationships between source monitoring and executive processes. Surprisingly, they reported either a total, partial or non-existent relationship between source monitoring and executive tasks. In order to understand and explain these contradictions, we classified the source and executive tasks of the 16 papers according to two well-accepted definitions. Source tasks were classified using the Source Monitoring Framework (Johnson, Hashtroudi, & Lindsay, 1993) which specifies reality and external and internal source monitoring. Executive tasks were classified according to the model of Miyake Friedman, Emerson, Witzki, and Howerter (2000) which specifies complex, shifting, updating and inhibition tasks. We found that evaluation of reality and internal source monitoring was limited. Regarding executive functions, there was no assessment of updating and only a limited assessment of shifting and inhibition. Therefore, the relationship between source monitoring and executive functions remains an open question. Our findings point to the need for the simultaneous assessment of source monitoring and executive functions as defined by multidimensional theoretical frameworks. Such investigations would help in understanding the relationship between specific source monitoring deficits and specific executive decline in clinical populations.

Destination memory in mild Alzheimer's Disease

In order to assess their destination memory, sixteen patients with probable mild Alzheimer Disease (AD), sixteen older adults and 16 young adults were asked to tell facts to pictures. On a subsequent task, they were asked to remember whether they had previously told that fact to that face or not. AD patients showed poorer destination recall than the older adults, and the older adults showed poorer destination recall than the young adults. Our results suggest that destination memory is highly impaired in AD.

Phenomenological Reliving and Visual Imagery During Autobiographical Recall in Alzheimer's Disease.

Multiple studies have shown compromise of autobiographical memory and phenomenological reliving in Alzheimers disease (AD). We investigated various phenomenological features of autobiographical memory to determine their relative vulnerability in AD. To this aim, participants with early AD and cognitively normal older adult controls were asked to retrieve an autobiographical event and rate on a five-point scale metacognitive judgments (i.e., reliving, back in time, remembering, and realness), component processes (i.e., visual imagery, auditory imagery, language, and emotion), narrative properties (i.e., rehearsal and importance), and spatiotemporal specificity (i.e., spatial details and temporal details). AD participants showed lower general autobiographical recall than controls, and poorer reliving, travel in time, remembering, realness, visual imagery, auditory imagery, language, rehearsal, and spatial detail-a decrease that was especially pronounced for visual imagery. Yet, AD participants showed high rating for emotion and importance. Early AD seems to compromise many phenomenological features, especially visual imagery, but also seems to preserve some other features.

Apolipoprotein E (APOE) ε4 and episodic memory decline in Alzheimer’s disease: A review

A growing body of research has examined the relationship between episodic memory decline, the cognitive hallmark of Alzheimers disease (AD), and the presence of Apolipoprotein E ε4 (APOE ε4) allele, a major genetic risk factor for the disease. Our review attempts to summarize and critically evaluate this literature. We performed a systematic search for studies assessing episodic memory in AD patients who were genotyped for APOE ε4 and identified fourteen papers. Although most of these papers reported significant relationships between APOE ε4 and episodic memory decline in AD, some papers did not confirm this relationship. Our review links this controversy to the conflicting literature about the effects of APOE ε4 on general cognitive functioning in AD. We identify several shortcoming and limitations of the research on the relationship between APOE ε4 and episodic memory in AD, such as small sample sizes, non-representative populations, lack of comparison of early-onset vs. late-onset disease, and lack of comparison among different genotypes that include APOE ε4 (i.e., zero, one, or two ε4 alleles). Another major shortcoming of the reviewed literature was the lack of comprehensive evaluation of episodic memory decline, since episodic memory was solely evaluated with regard to encoding and retrieval, omitting evaluation of core episodic features that decline in AD, such as context recall (e.g., how, where, and when an episodic event has occurred) and subjective experience of remembering (e.g., reliving, emotion and feeling during episodic recollection). Future research taking these limitations into consideration could illuminate the nature of the relationship between APOE ε4 and episodic memory decline in AD.