How older employees perform in the workplace

IF YOU ARE over 20, look away now. Your cognitive performance is probably already on the wane. The speed with which people can process information declines at a steady rate from as early as their 20s.

A common test of processing speed is the “digit symbol substitution test”, in which a range of symbols are paired with a set of numbers in a code. Participants are shown the code, given a row of symbols and then asked to write down the corresponding number in the box below within a set period. There is nothing cognitively challenging about the task; levels of education make no difference to performance. But age does. Speed consistently declines as people get older.

Why this should be is still a matter of hypothesis, but a range of tentative explanations has been put forward. One points the finger at myelin, a white, fatty substance that coats axons, the tendrils that carry signals from one neuron to another. Steady reductions in myelin as people age may be slowing down these connections. Another possibility, says Timothy Salthouse, director of the Cognitive Ageing Laboratory at the University of Virginia, is depletion of a...