Objective: This paper revolves around the interface between psychogeriatrics and evolutionary biology: a new phylogenetic model of memory in dementia of the Alzheimer type (DAT) is introduced that increases understanding of DAT.
Design: The design is an exhaustive, computer-based, exploratory review of forty years of DAT memory investigations to determine: 1) What is diachronic pattern of DAT memory deficits, 2) What are main memory paradigms used to describe DAT memory deficits, 3) There is/is not a descriptive and explanatory goodness-of-fit between major memory paradigms and data relating to DAT memory decline over time.
Materials and Method: This paper is an empirically-based theoretical discussion of the nature and patterns of memory deficits in DAT. To identify published studies on memory in DAT, an exhaustive computerized literature search spanning the past forty years was performed. The use of Medline, PsychLIT, PsychINFO, and Dartmouth Biomedical INFO/ED computerized databases resulted in 1,035 references that were examined. Because of definitional changes across time, reviewing investigations of memory in DAT involved methodologic problems such as that of phenomenal identity, whereby different patient populations are labeled with an identical term and identical populations are labeled with different terms, as well as other uncontrolled variation across samples compared.
Results: The computerized literature search found there is lack-of-goodness of fit between the five most prominent memory frameworks used to describe memory in DAT and empirical findings relating to memory deficits of the Alzheimer's patient. Data suggest that the phylogenetic context of memory is critical for understanding memory deterioration in DAT. Memory is a phylogenetically evolved structural and functional system enabling organisms to adapt to physical and social environments. Phylogenetically, human memory appears to be a product of modified old brain parts and newer brain parts working together, having evolved over millions of years. Empirical data are presented suggesting DAT memory deterioration involves a process of phylogenetic retrogression because memory structures last to evolve in phylogenesis deteriorate first in DAT. A data-based new three-tiered evolutionary model of memory in DAT is introduced, each tier originating in a different period of phylogenetic history: motor memory, emotional memory, neocortical memory.
Conclusion: Memory frameworks currently in use, overall, lack a diachronic dimension and, in consequence, fail to reflect the reality that memory is an evolved set of systems working together to enable organismic adaptation. The process of dementing in the Alzheimer's patient is better understood when one understands that memory deterioration in DAT involves a phylogenetic retrogression whereby greatest and earliest memory deficits occur at the neocortical tier. Data is presented which suggest that, relative to themselves and other dementia populations, i.e., subcortical dementias, DAT memory deficits appear greatest and earliest on neocortical memory tasks as compared to motor or subcortical memory tasks or tasks of emotional remembrance. Accordingly, the phylogenetic memory framework introduced in this paper enables increased understanding of DAT.
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