We all know that cognitive ability gets worse as we age.  Even healthy older adults think more slowly and remember less than healthy young adults.  The declines are slow and steady, though clearly not debilitating.  Many older adults continue to make important and productive contributions to their fields into their 70s and 80s and beyond.

An interesting question about the performance of older adults is whether the declines reflect that older adults are just worse than younger adults on a day-to-day basis or whether older adults are more variable.  That is, do older adults have more extreme good days and bad days than younger adults?

This issue was explored in a paper by Florian Schmiedek, Martin Lovden, and Ulman Lindenberger in the September, 2013 issue of Psychological Science.  They analyzed data from a long-term study of Germany younger adults (on average 25 years old) and older adults (on average 71 years old).  Each participant completed roughly 100 sessions of a battery of cognitive tasks measuring memory skills, perceptual ability, and working memory capacity.  (Working memory is the ability to hold onto information in the moment to use it during thinking.)  Overall, participants performed 9 tests in each session.

Participants did this battery of tests at least twice a day during the study period, so that it was possible to disentangle variability in performance that was just a result of different times of day and variability in performance that was due to having good days and bad days.

Overall, the older adults performed less well on the variety of cognitive tests than the younger adults.  Interestingly, the older adults were more consistent in their performance over time than the younger adults.  The older adults showed less variability across all of the different tasks both from one time of day to another and from one day to the next than the younger adults.

This finding helps to explain why declines in cognitive performance with age are not debilitating to older adults.  Even though older adults do get worse overall, their performance stays within a narrow range from day-to-day.  Generally speaking, older adults do not have rapid swings from really good days on which they perform exceptionally well to really bad days on which they fall apart.  This low level of variability helps older adults to maintain reasonable performance each day.

Indeed, one of the signs of significant declines in aging associated with senile dementia and Alzheimer’s disease is that there is a lot of daily variability in performance.  The rapid daily changes associated with these disorders cause real problems for patients.  They also serve as a warning sign for people who are on the lookout for cognitive problems in themselves or aging relatives.

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