Use It Or Lose It

The mind, apparently, is much like any other capital good. It depreciates and obsolesces over time unless there is considerable and continuing maintenance and reinvestment. Optimizing with respect to this investment over time is a typical investment decision involving uncertain outcomes.

Further evidence that continuing mental activity and exercise helps stave off deterioration in later years (i.e., reduce the rate of depreciation) is summarized in this article in the Washington Post (registration required).

A large body of evidence indicates that people who are mentally active throughout their lives are significantly less likely to suffer senility, and a handful of studies have found that mental exercises can boost brain function. Elderly people who go through training to sharpen their wits, for example, score much better on thinking tests for years afterward. The minds of younger people who drill their memories seem to work more efficiently.

... Among the most tantalizing evidence are studies that have given rise to the use-it-or-lose-it theory. Several large projects have found that people who are more educated, have more intellectually challenging jobs and engage in more mentally stimulating activities, such as attending lectures and plays, reading, playing chess and other hobbies, are much less likely to develop Alzheimer's and other forms of dementia.

Scientists suspect that a lifetime of thinking a lot may create a "cognitive reserve" -- a reservoir of brain power that people can draw upon even if they suffer damaging silent strokes or protein deposits that are the hallmarks of Alzheimer's.

Ms. Eclectic and I spend a lot of time doing crosswords and sudoku together. I hope it helps.