When I took up brain training I never expected to find such a strong connection, or any connection, between brain exercise and my happiness level. On days when I'm in a good mood, I do better at the brain exercise; and on days when I do the brain exercise, it makes me feel happier and more relaxed. My fellow brain trainers report the same thing.

Recent scientific research would seem to shed light on both aspects of this phenomenon. Beginning with research performed by Dr. Richard Davidson at the University of Wisconsin in 2005, scientists have consistently found that the brains of those who meditate (such as Tibetan monks in Davidson's study) function differently than normal brains. The firing of neurons is better coordinated and more intense.

This seems to be what is happening when I am calm, relaxed and focused during brain training. And the effect seems to be enhanced when I take a break and meditate between training blocks. My brain fires more evenly; I can concentrate better, and my working-memory functions more effectively. Conversely, when I'm not feeling meditative, my attention is fractured and my brain quickly loses short-term information.

Another telling aspect of the research findings is that the more we practice these skills of mindful meditation, the more our brain responds.

The second aspect of the relationship between brain-training and a sense of well-being is equally profound and exciting. Two recent studies hone in on the way that depression works on a neural level. One reveals that antidepressants need new nerve cells to be effective. The study by researchers from UT Southwestern Medical Center showed that the effectiveness of anti-depressants in mice depends upon the growth of new nerve cells in the part of the brain known as the dentate gyrus. The other study by German researchers found that stress inhibits new neural cell growth, thereby contributing to depression.

Fortunately, we can do two things to help generate new nerve cells in the dentate gyrus: aerobic exercise and working-memory activation. Aerobic exercise of course has many positive results and has long been associated with mood elevation. Increased blood flow in the brain helps stimulate neural growth. It's been less well understood however that certain kinds of mental task can stimulate new cell growth.

Not all brain exercises will be pronounced enough to stimulate significant neural growth. Casual brain teasers or games that don't demand concerted focus and attention for an extended period are unlikely to produce these results. New nerve cell growth demands intense concentration at a novel and rewarding mental task.

It pays to check the scientific pedigree of the training exercises the training program incorporates. Does the vendor specify what the training will accomplish, what measurable gains to expect in memory or processing ability? Does the product come with a training schedule, indicating how much time you should devote to the exercises and over what period?

As with any form of exercise, brain exercise rewards in equal measure to our investment. We can't expect to stay physically fit without breaking a sweat - so, too, a truly effective brain training program requires our attention and effort. The rewards to our mental health and happiness, however, can repay every ounce of that investment.