Choosing wisely what you chow down for lunch or how you spend your free time may not only improve physical health, but can also boost your brain's performance, according to a growing body of research. Which are the best foods, supplements, and activities to improve cognitive function? Here are top choices from Georgetown, Massachusetts-based neuropsychologist Diane Stoler, EdD.

Favor dark chocolate
For a quick mental boost, Stoler recommends dark chocolate. "Research has proven that dark chocolate contains certain chemicals that enhance mental clarity," she says. Flavonoids found in cocoa, for example, help reduce both blood pressure and insulin resistance, conditions that can affect mental performance (Hypertension, 2005, vol. 46, no. 2).

Boost with B vitamins
Stoler recommends taking a vitamin-B complex, which has been shown in numerous studies to improve memory and protect the brain against mental disorders. New research reported in the American Journal of Medicine found that low B-vitamin and folate levels may contribute to cognitive decline (2005, vol. 118, no. 2). In addition, Stoler advocates supplementing with spirulina. The algae are rich in antioxidants and full of brain-beneficial nutrients, such as omega-3 fatty acids. (To learn more about spirulina, see "Green Foods.")

Breathe deeply, consciously
Researchers confirm what yogis have known for thousands of years: Clear breathing equals clear thinking. A study performed at the University College London demonstrated a positive association between lung function and cognitive ability in more than 1,700 participants (Psychosomatic Medicine, 2005, vol. 67, no. 4). Incorporate a sustained set of deep-breathing exercises (in yoga known as pranayama) to enhance mental clearness, suggests Stoler. Relax your mind and breathe in through the nose for a count of six. Exhale slowly for a count of eight while visualizing a release of stress from the body.