Distinguishing preterminal and terminal cognitive decline

This paper reviews different methodological approaches taken to examine terminal decline in cognitive function, and presents new findings from the Bronx Aging Study (BAS). Numerous approaches have been taken to assess mortality effects on cognition: comparing survivors and decedents level and rate of change in cognition, and identifying individual differences in cognition asociated with time-to-death. However, few studies have actually modeled within-person change in cognition as a function of time-to-death. Using linear mixed models with a change point, intraindividual change in episodic memory was modeled as a function of both age and time-to-death. A dramatic increase in the rate of decline was identified at 8.4 years prior to death, providing clear evidence of a terminal-decline phase that is much longer than previously estimated. These results emphasize the importance of modeling the time course and effects of terminal cognitive decline for understanding cognitive change in aging adults.