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Study finds: Some memories are more vulnerable to dementia than others

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New research indicates that some autobiographical memories are more vulnerable to Alzheimer’s disease and dementia than others.

The study examined 11 patients with a clinical diagnosis of probable Alzheimer’s disease and 13 patients with frontotemporal dementia. Another 23 healthy older adults were recruited as controls. Repeated testing and brain imaging revealed that more recent autobiographical memories became more vulnerable to loss as frontotemporal dementia became more severe. Among the patients with Alzheimer’s disease, on the other hand, the ability to recall autobiographical memories did not appear to worsen overall as the disease progressed.

The study also uncovered that changes in autobiographical memory retrieval were associated with different regions of the brain in Alzheimer’s disease and frontotemporal dementia. The findings were published March 10, 2017, in the journal Neuropsychologia.

PsyPost interviewed the study’s corresponding author Muireann Irish of the University of Sydney. Read his explanation of the research below:

PsyPost: Why were you interested in this topic?

Irish: Autobiographical memory, to me, is one of the most fascinating expressions of human cognition. A large part of my research program seeks to understand how we mentally travel back in subjective time to relive evocative and personally defining events from our past, and to clarify the brain regions that must be functional to support this complex process. Loss of autobiographical memory represents a hallmark feature of many dementia syndromes, yet it remains unclear whether all memories suffer the same fate with advancing disease severity. Longitudinal studies exploring how personally relevant memories are affected over time in dementia are scarce, although such approaches are crucial to provide a comprehensive picture of the dementia trajectory. We sought to investigate how autobiographical memory potentially changes as different dementia syndromes unfold over time, and to elucidate the neural substrates of these changes.

What should the average person take away from your study?

Our study reveals that not all personal memories are created equal. While some memories seem vulnerable to decay, others appear relatively resilient in the face of worsening cognitive decline. Moreover, different dementia subtypes display distinct profiles of memory loss over time. Importantly, we demonstrated that recent memories, those experienced within the previous year, are much more vulnerable with disease progression in frontotemporal dementia and that this loss of recent memory is associated with the spread of atrophy into a region called the posterior cingulate cortex. This region has previously been associated with the encoding and retrieval of recently experienced events in healthy individuals, and as such, our findings dovetail nicely with the existing literature.

A somewhat surprising finding was our observation of equivalent performance across baseline and follow-up assessment periods in patients with Alzheimer’s disease. We had predicted that autobiographical memory would gradually decline over time in these patients, yet no significant differences were observed. Our neuroimaging analyses revealed the increasing involvement of brain regions known to support semantic memory or general knowledge over time in this group. We tentatively interpret this finding as reflecting the retrieval of memories that have become more semantic or fact-like with the passing of time. This process, known as semanticization, is typically observed for older memories from the distant past, and can account for the well-documented finding of relatively intact retrieval of memories from one’s childhood and early adulthood in individuals with Alzheimer’s disease.

Are there any major caveats? What questions still need to be addressed?

While our findings are interesting, one limitation is that the time between baseline and follow-up assessments for this study was only one year. This was important to ensure that patients could continue to participate in the study, but it also means that we do not have a clear picture of how memories potentially decline over longer durations of time. From a practical point of view, it will be essential to clarify what mechanisms facilitate the successful retrieval of autobiographical memories in dementia, in order to inform the development of reminiscence programs and targeted interventions. Our findings, while preliminary, suggest that it may be possible to target memories that have become ‘semanticized’ in certain dementia types to promote a connection to the past.

Is there anything else you would like to add?

Our autobiographical memories are central to our sense of personal identity and continuity across subjective time. Understanding how the loss of these memories impacts the individual in terms of their sense of identity and their ability to engage meaningfully with others is crucial for improving dementia care. Our study demonstrates that there exists a store of autobiographical memories that remain relatively intact in certain dementia syndromes until well into the more moderate stages of the disease. Devising novel means to bolster the retrieval of such memories will be an important next step.

In addition to Irish, the study “Evolution of autobiographical memory impairments in Alzheimer’s disease and frontotemporal dementia – A longitudinal neuroimaging study” was also co-authored by Ramon Landin-Romero, Annu Mothakunne, Siddharth Ramanan, Sharpley Hsieh, John R. Hodges, and Olivier Piguet.

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