Longitudinal profiles of terminal decline: associations between cognitive decline, age, time to death, and cause of death

Abstract

Normative age differences and declines in cognition may be overestimated due to influences reflecting impending mortality. The terminal decline hypothesis posits that accelerated cognitive decline for older adults is a function of proximity to death. Although previous research has demonstrated mortality-cognition associations, key questions remain unresolved. This study examined five neglected aspects of terminal decline research: (a) are mortality deficits uniform across age? (b) does impending mortality differentially influence cognitive domains? (c) does cause of death influence magnitude of mortality deficits? (d) do individuals closer to death show accelerated cognitive declines? and (e) do mortality deficits share associations with indicators of neurological disturbance such as performance inconsistency? The sample consisted of 707 adults from the Victoria Longitudinal Study (VLS) who completed between 1 to 5 waves of measurement over a 12-year period. Participants were classified as either Young-Old (59 to 79 years, M = 71.86) or Old-Old (80 to 95 years, M = 83.66). A total of 442 Survivors completed all waves and relevant measures compared with 265 Decedents who participated on at least one occasion and subsequently died. An extensive battery of tests was administered including measures of verbal speed, working memory, episodic memory, semantic memory, and crystallized verbal ability. Results were informative for each of the five research questions. First, mortality-related cognitive deficits were magnified with increasing age. Old-Old decedents exhibited steeper decline compared with similarly aged and younger survivors. Further, multilevel analyses demonstrated that Decedents declined at significantly faster rates per year increase in age. For the second research question, terminal decline was found to differentially influence select cognitive measures. Relative to Survivors, Old-Old Decedents displayed large variation across measures exhibiting poorer performance for verbal speed and episodic memory with considerably better performance for vocabulary. Results for the third research goal demonstrated that specific cause of death differentially influenced cognitive performance. Greater cross-sectional differences and declines were found for those who died of cardiovascular disease (CVD). A fourth contribution to the terminal decline literature found that the shape of cognitive decline for Decedents was accelerated in closer proximity to death. Evidence for the final research question revealed that impending death, presence of CVD, and older age were all associated with increased performance inconsistency. Considered together, these results provide both converging evidence and novel contributions to the terminal decline literature.

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