Meditation. Mindfulness. Both have been practiced since as early as 1500 BC and are still widely practiced today. Researchers have been studying the brain with advanced diagnostic equipment (CT/MRI/FMRI) the last few years and have uncovered some astounding information.
Recently, a team led by Harvard-affiliated researchers at Massachusetts General Hospital (MGH) have linked mindfulness and meditation to increased neuroplasticity and increased gray matter density in the hippocampus- the part of the brain largely involved in learning and memory/information recall. Basically meditation and mindfulness can help keep the brain healthy and keep you "sharp."
I spent some time at the Miller School of Medicine a few years ago where ICAMP (Integrative & Complementary Academic Medicine Programs) hosted numerous speakers. One speaker, Dr. Aviad Haramati, tenured and renowned professor of physiology from Georgetown University, spent his 90 minute presentation talking about chronic stress and it's effects on all systems of the body. During his lecture he spoke largely in part about modulating stress through mindfulness and meditation. Since then I have been practicing mindfulness/meditation twice a week (often in the infrared sauna) and can attest to the healing nature of the practice.