Over the hill earlier than we thought?

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by Erin Brown, Science Correspondent

Youth just got a lot shorter, as far as mental life is concerned.

That mental abilities tend to suffer as we get older, particularly after the age of 60, is a well-established fact.  But according to a recent report in the journal Neurobiology of Aging, cognitive function appears to begin its decline at around 27, an age much earlier than traditionally accepted. Dr. Timothy Salthouse from the University of Virginia combined various methods for assessing mental acuity, including tests of inductive reasoning, spatial visualization, episodic memory, and perceptual speed.  Scores peaked at 22 and remained steady until 27, at which point the decline became statistically significant.

Salthouse claims that his study accounts for potentially confounding factors, noting the results remain significant after variables like education level, self-rated health, number of medications taken per week and self-reported measures of depression and anxiety are controlled for.

Most readers will probably find this research a bit unsettling (particularly those of us who are, apparently, already ‘past our prime’).  However, a few important points to consider may provide some comfort.

To begin with, the relationship between age and cognitive decline is correlational, meaning getting older doesn’t necessarily cause loss of function. There could potentially be many unaccounted for variables that are responsible for the observed pattern, especially for a trait as complex and nebulous as human cognition.

So if age and the controlled for factors aren’t the whole story, what likely alternative could help to explain the trend?

One unaddressed possibility is the effect of a western, middle-class lifestyle.  Cognitive demand and stimulation are not constant throughout our lifetimes.  The first 18-25 years are spent learning, both academically and socially. But eventually our education stops (or slows significantly), and sometime during our mid-twenties we begin to settle into a career.

The highly specialized nature of western society, coupled with the traditional model of working in the same field, industry or company until retirement, means the average person doesn’t experience a whole lot of variety.  For many, daily life ceases to offer substantial intellectual stimulation or novelty.

Now also consider the well-documented evidence that an enriched environment and high levels of mental stimulation can increase neural plasticity and improve cognitive function.  Doctors have known for some time that interaction and mental engagement can ameliorate or reverse dementia and improve cognitive test performance.  Mental abilities, therefore, are not fixed, but can be enhanced or deteriorate through experience.

With this in mind, Salthouse’s research can be interpreted somewhat differently.  The peak age for test scores was 22 – a time often associated with either the height of academic education or learning new skills in job training.  The initial decline at 27 coincides with a point at which many people have begun their careers and stopped acquiring skills and knowledge at a rate comparable to the preceding years.  The steady decline up to 60 and beyond may be associated with what sadly amounts to intellectual stagnation.

So loss of mental sharpness corresponds to a similar decrease in diversity of experience, which may be at least partially responsible for the reported pattern of test scores.  Thus, instead of responding with panic or defeated acceptance in light of the connection between age and mental decay, we can take comfort in the fact that loss of cognitive abilities is not inevitable.

It may also be wise to contemplate whether the conventional way of life in our society adversely affects our intellectual lives.  Humans thrive on variety.  Unfortunately, the typical occupation is characterized more by monotony and tedium, providing little satisfaction for our multifarious psychological needs.  Perhaps the vocational and professional structure of our culture could be adapted so that a person’s lifetime contribution to society is not to the detriment of their mental and emotional well-being.

Comments?  Please feel free to contribute to the discussion by adding your comments below…

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