Just as different sports target different parts of the body, Lumosity's games target specific functions in the brain, such as attention, memory, or processing speed. The games work by stimulating the brain's neuroplasticity, which refers to how your neurons and connectors change in reaction to experiences in every day life. Neuroplasticity can actually help neurons compensate for diseases or injuries, and react to new situations. Certain activities, ranging from dancing to games that test your brain, influence your plasticity and help you stay sharp.
If you want to try some of Lumosity's games, Popsci.com has three you can play right now (for free!). Speed Match works on attention and memory; Word Bubbles improves vocabulary; and Memory Matrix beefs up the part of your brain in charge of remembering names, the locations of objects, and reasoning.