We aren't so much talking about the physical structure of the brain itself - or are we? Medical and psychological research recently has pointed to the emerging idea that the more you exercise your brain, the better it will work in your old age and the more resistant you will be to Alzheimer's, dementia, and general cognitive impairments. It is very difficult to say exactly how this works - what, for instance, are we to make of the recent clinical test where a group who was taught how to juggle showed a marked improvement in abstract intelligence after one month?

It is becoming certain that the less people exert themselves mentally, the less able they are to handle mental exertion. The classic case is the "couch potato", particularly someone with a desk job by day and not much recreation beyond watching television at night. "Use it or lose it." An interesting footnote to the couch potato effect is that the acts of sitting still and staring at a lit screen for periods of time don't seem to be the causes of mental atrophy in themselves. Computer users do the same thing, but the difference is that computers are interactive while television demands that you sit and watch and thus, computer users - even if they're just playing video games - tend to keep their mental skills sharp where the television-watchers slowly lose their edge.

Of course, the physical atrophy of the brain is somewhat uncovered. Cerebral atrophy, which is the loss of neurons and the connections between them, has been pinpointed as a symptom or associated effect of strokes, Alzheimer's, cerebral palsy, epilepsy, and many other diseases in which mental acuity is decreased. By the time any of these have set in, however, it is too late to take a preventative measure.

But our purpose here is to talk about the stimulation of a healthy brain in order to keep it healthy. And there is a mounting body of evidence that it is quite possible to do just that. Some of the latest findings are:

* Neuroscience researchers at Northwestern University have uncovered the first concrete evidence that playing music can significantly enhance the brain and sharpen hearing for all kinds of sounds. Experience with music appears to help with many other things in life. Such activities as reading or picking up nuances in tones of voices or hearing sounds in a noisy classroom better are all sharpened by playing music.

* Neurologists at Columbia University Medical Center in New York have discovered that (physical) exercise boosts brainpower by building new brain cells in the brain regions linked with memory and memory loss. Tests on mice showed that they grew new brain cells in a part of the hippocampus that is known to be affected in the age-related memory decline that begins around age 30 for most humans.

* Researchers at the University of Rochester have shown that people who played action video games for a few hours a day over the course of a month improved their performance on a visual acuity test. The conclusion is that action-based video game play changes the way our brains process visual information.

* In a study by researchers at the Wellcome Trust Center for Neuroimaging at UCL's Institute of Neurology, a series of brain scans performed on taxi drivers and bus drivers showed that the mid-posterior hippocampus of all the taxi drivers was bigger and that they had more gray matter than the bus drivers. The one big difference between the two is that bus drivers stick to routes, while taxi drivers have to learn the layout of the whole city.

The downside of our new technology age just might be that having more and more electronic convenience devices exerts a terrible toll in robbing the brain of needed stimulation. In the taxi driver study above, the researchers advocated against using a GPS system to navigate, because of course that's one more robot doing the thinking for you - and one less source of stimulation to the brain!

If you have a patient who you think would benefit from some mental stimulation, here are some ideas you might want to try out. The good news is that none of these are sheer drudgery - encourage the patient to think of them as little games, or to pick something they will enjoy.

* Toss the calculator. Re-learn how to do sums in your head, for instance in figuring the tip at restaurants or mentally keeping a tally on the total price of items in your cart when you do grocery shopping. Stress that the point of this is not to become a human calculator, but to see how close you can come with practice. For the grocery shopping, rounding prices to the nearest dime and recalling the current total at the end of each aisle is quite easy, and you'll often find yourself off by no more than a dollar by the time you check out - even on a $200 purchase!

* Make out a grocery list or to-do list - but then as you run the errand, don't look at the list! The simple act of writing things down helps your brain remember the list, and you can always peek at it if you forget an item. Keep at this practice until you can do without a list at all.

* Do word puzzles like crosswords and jumbles. Make a habit of seeking the puzzle out every day in the newspaper. Again, the object is not to become perfect at it - but just starting the crossword and seeing how far you get at it is enough to practice a little while.

* Do other kinds of puzzles. These include mazes, spatial reasoning brain-teasers, and the popular soduku puzzles. These have the same benefits as the word puzzles, but exercise different areas of the brain.

* Learn a new word per week. Not just looking it up, but also using it a few times in conversation. The rule of thumb is "Say it three times and it's yours." Our thoughts, in a manner of speaking, are made up of words, and so each new word we learn allows us to think new thoughts.

* Take up a new hobby or activity. It doesn't have to be an all-consuming pursuit or even an expensive one. Simple pastimes like orgami, poetry recital, telling jokes, juggling, assembling jigsaw puzzles, sketching, or bird watching are cheap and simple to participate in, and provide many benefits. The idea is more to step out of your "comfort zone" and challenge yourself to master a new activity that you never thought of yourself doing.

* Get more involved with your computer and other electronic devices. Really read the owner's manual and learn how to use all the features - less than one percent of us actually do that! take up a new technology-related skill such as web design or programming - these are not at all as hard as people think they are! Or before throwing away an old computer or a broken VCR, try taking it apart first. See if you can figure out why it broke, or how it works at all. Look up a diagram on the device and see if you can identify the major parts.

* Lose your Microsoft Windows dependency and try a new Open Source operating system, one that you can download for free, such as Linux or BSD. These operating systems are like little computer science lessons, teaching you how computers work and forcing you to confront and solve more situations than an environment that does everything for you.