From a reasonably large British study
The British Medical Journal reported that:
Longitudinal modelling of cognitive decline using three measures over 10 years provides robust evidence of cognitive decline at all ages between 45 and 70, even among those aged 45-49 at baseline
The 10 year decline in reasoning was −3.5% in men aged 45-49 at baseline and −9.6% among those aged 65-70; the corresponding figures for women were −3.6% and −7.4%
© 2012 Archana Singh-Manoux, Mika Kivimaki, M Maria Glymour, Alexis Elbaz, Claudine Berr, Klaus P Ebmeier, Jane E Ferrie, and Aline Dugravot, Timing of onset of cognitive decline: results from Whitehall II prospective cohort study, British Medical Journal [BMJ], doi: 10.1136/bmj.d7622 (05 January 2012) (at closing section entitled, “What this study adds”)
How the study was done
A group of 10,308 British civil servants (67 percent of which were men) were followed, beginning in the period from 1985 to 1988. This sample was divided into five age groups: 45-49, 50-54, 55-59, 60-64, and 65-70.
Initially, the groups received a clinical medical exam, as well as a self-administered questionnaire. Cognitive testing began between 1997 and 1999:
The Alice Heim 4-I (AH4-I) is composed of a series of 65 verbal and mathematical reasoning items of increasing difficulty. It tests inductive reasoning, measuring the ability to identify patterns and infer principles and rules.
Participants had 10 minutes to do this section. Short term verbal memory was assessed with a 20 word free recall test. Participants were presented a list of 20 one or two syllable words at two second intervals and were then asked to recall in writing as many of the words in any order within two minutes.
We used two measures of verbal fluency: phonemic and semantic. Participants were asked to recall in writing as many words beginning with “S” (phonemic fluency) and as many animal names (semantic fluency) as they could.
One minute was allowed for each test; the observed range on these tests was 0-35. Vocabulary was assessed with the Mill Hill vocabulary test, used in its multiple choice format, consisting of a list of 33 stimulus words ordered by increasing difficulty and six response choices.
© 2012 © 2012 Archana Singh-Manoux, Mika Kivimaki, M Maria Glymour, Alexis Elbaz, Claudine Berr, Klaus P Ebmeier, Jane E Ferrie, and Aline Dugravot, Timing of onset of cognitive decline: results from Whitehall II prospective cohort study, British Medical Journal [BMJ], doi: 10.1136/bmj.d7622 (05 January 2012) (at “Cognitive function” section) (paragraphs split)
My caveat on the authors’ caveat
The authors assume that their study under-estimates cognitive decline. They appear to reason that this occurs for two reasons:
First, people being retested remember the tests from their earlier sessions. So their scores are higher due to the “practice effect.”
Second, an increasing proportion of older people (presumably having become less cognitively capable) don’t respond at all in subsequent sessions.
Both reasons make sense, provided we allow a loose definition of “practice.”
I know from experience (having been quite late in undertaking medical and law school) that my mind was considerably less facile, especially in regard to rote memorization, than it had been when I was 20.
On the other hand, I also noticed that my analytical speed and memory sped up markedly with practice (as in solving chemistry and physics problems), even at my then comparatively late ages (47 and 52).
Of course, my acuity in some subjects afterward declined equally fast with disuse — as, for example, with my ability recall formulas and to apply them to quantitative problems just a few years after the applicable courses had ended.
What I’m driving at here is that I would like to see a comparison of weekly practiced older people against their equally practiced younger selves.
I am not convinced that the authors are correct in thinking that one’s innate (but daily honed) cognitive ability actually drops even faster than their study reported. And I certainly do not buy the idea that being tested every five years amounts to “practice” in the sense that most people understand it.
The moral? — we almost certainly do get less acute with age, but how much of this reflects an actual decline in innate capacity is arguably uncertain
I am not yet persuaded that we cannot “practice” some (but not all) of our cognitive decline away.