18 January 2010

The passive brain

This study of Australian TV viewers (found via Middle of Nowhere) confirms what we pretty much knew all along -- that excessive TV-watching shortens your life, even when other risk factors such as weight are corrected for. It has long been known that a sedentary lifestyle and lack of exercise speed up the aging process.

What's interesting, though, is that the factors corrected for in the study included exercise habits -- that is, there's a correlation between longer hours in front of the TV and earlier death even between people whose exercise habits are similar. So it's not just that TV addicts die sooner because they exercise less. There's something more beyond that.

TV-watching differs from other physically-inactive behaviors -- such as reading the internet, sitting at a desk working, or doing crossword puzzles -- in one very obvious way: the extreme mental passivity it requires. Those other activities are highly interactive; you're making decisions all the time, operating the computer or writing things down, controlling what's happening. Even when reading a book, you may slow down to read a challenging passage more carefully, or skip a boring one, or go back to take a second look at something you're not sure you fully absorbed. You stop and start as you choose.

(I suspect that the fact that seeing images and hearing sound are natural to us, while reading and understanding print is a learned behavior, plays a role. Extracting information from lines of text must make your brain work harder than watching images and hearing speech, simply because the former comes less naturally to it than the latter.)

Watching TV has no such interactive quality. It's purely a one-way flow of information. The program comes on when it comes on, not when you decide you want to start (or stop) watching. You can't speed it up, slow it down, or go back. Your brain has nothing to do. Brainwaves of people watching TV become reduced in a way reminiscent of sleep. It seems fairly obvious that that wouldn't be the case in people surfing the net or doing crossword puzzles.

Everyone knows that muscles which are not exercised become weaker, while exercise makes them grow stronger. This "use it or lose it" phenomenon applies to the brain as well. Old people who regularly engage in some kind of stimulating mental activity tend to keep up their full mental faculties better then those who don't.

Deterioration of mental sharpness might well shorten life. It would surely make life less worth living.

A glance at a typical cross-section of Americans affirms that over-eating and lack of exercise are our most pressing health problems, and those things should remain the focus of any effort to improve health. But even among the physically inactive ways in which we spend so much of our time, not all are equally bad.

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