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. 2011 May;66(3):292-301.
doi: 10.1093/geronb/gbr001. Epub 2011 Feb 7.

Aging and the shape of cognitive change before death: terminal decline or terminal drop?

Stuart W S MacDonald  1 , David F Hultsch, Roger A Dixon
Affiliations

Aging and the shape of cognitive change before death: terminal decline or terminal drop?

Stuart W S MacDonald et al. J Gerontol B Psychol Sci Soc Sci. 2011 May.

Abstract

Objectives: Relative to typical age-related cognitive decrements, the terms "terminal decline" and "terminal drop" refer to the phenomenon of increased cognitive decline in proximity to death. Given that these terms are not necessarily synonymous, we examined the important theoretical distinction between the two alternative trajectories or shapes of changes they imply.

Methods: We used 12-year (5-wave) data from the Victoria Longitudinal Study to directly test whether pre-death cognitive decrements follow a terminal decline (generally gradual) or a terminal drop (more abrupt) shape. Pre-death trajectories of cognitive decline for n=265 decedents (Mage = 72.67 years, SD = 6.44) were examined separately for 5 key cognitive constructs (verbal speed, working memory, episodic memory, semantic memory, and crystallized ability).

Results: Several classes of linear mixed models evaluated whether cognitive decline increased per additional year closer to death. Findings indicated that the shape of pre-death cognitive change was predominantly characterized by decline that is steeper as compared with typical aging-related change, but still best described as slow and steady decline, especially as compared with precipitous drop.

Discussion: The present findings suggest that terminal decline and terminal drop trajectories may not be mutually exclusive but could rather reflect distinct developmental trajectories within the same individual.

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Figures

Figure 1.
Figure 1.
The figure displays the mapping between theoretical implications of terminal decline versus drop and choice of statistical model for evaluating the distinction. Although often considered as evidence for terminal drop, a linear plus quadratic slope model is not necessarily the definitive choice for differentiating terminal decline from terminal drop. As shown in the figure, the significant linear plus quadratic trend may reflect a steadily accelerating, but nonetheless gradual, terminal decline spanning a period of years prior to death. Similarly, a linear spline model with an inflection point far from death (change point far inflection, or FI) may indicate increased decline following the change point, but similar to the displayed linear plus quadratic model, this decline is manifest in a more gradual fashion many years preceding death (10 years in the hypothetical example). However, a change-point model with an inflection point near death (change point near inflection, or NI) represents a reasonable statistical instantiation of terminal drop, with abrupt cognitive change occurring in close proximity to the death event (4 years in the example). A change trajectory characterized by a larger magnitude quadratic effect (not displayed) could also approximate the change point NI trajectory, consistent with terminal drop.
Figure 2.
Figure 2.
Linear and quadratic change in response latency for the semantic verification task per year closer to death.
See this image and copyright information in PMC

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