Have you made a New Year's resolution to get more exercise? Whether to improve your cardiovascular health or to help with weight control, exercise is a great plan. And now there is evidence that physical exercise can also perk up our brains.

This shouldn't be a surprise. If exercise is healthy for our hearts and lungs, then why not for our brains? And if exercise can improve brain function, then it may also be beneficial for mood, cognition, and overall mental performance.

Research studies have shown that moderately intense physical activity, and especially aerobic exercise like brisk walking and running, can lead to improvements in cognitive functions like attention, reasoning, and decision making. Experiments have compared groups of people who exercised regularly with others who did not. The improvements in brain function were most dramatic in older adults, but all ages appeared to benefit from increased physical exercise.

One recent analysis looked at the combined results of 18 different studies of the possible cognitive effects of fitness training in older adults. Although the results showed gains in all types of cognitive activity among the fitness-training groups, the greatest advances were found in the exercisers' executive functioning, which controls higher-level decision making skills like planning, scheduling, multi-tasking, and dealing with ambiguity.

We need executive functioning to be able to select appropriate social behaviors and inhibit inappropriate actions. Other types of cognitive activity include reaction time, the ability to remember or interpret visual information, and lower-level decisionmaking.

Surveys also show that people who are physically active throughout their lives are less likely to experience cognitive decline later in life. And those who exercise regularly are less likely to develop Alzheimer's disease.

Some clues may explain how physical activity can help the cognitive functioning of our brains. It has been shown, for example, that fitness training can improve blood flow in the brain and increase the number of capillaries carrying the blood.

Exercise also increases levels of neurochemicals that stimulate the interconnections among neurons. And exercise may increase the size of some areas of the brain or, at least, slow their rate of decrease as we age. Many of these changes are most prominent in the brain's frontal cortex, the area most important for executive functioning.

So remember, even modest increases in physical activity can be beneficial for your brain and for the important things that organ does for you. How much exercise is enough?

That depends on your age and health, but vigorous walking for 20 to 30 minutes a few days a week is a good start. Be sure to check with your health care provider before starting a new, rigorous exercise program.