The Shrink in Your Pocket

NEARLY EVERY DAY since she was a child, Alex Leow, a psychiatrist and computer scientist at the University Chicago, has played the piano. Some days she of Illinois plays well and other days her tempo lags and her fingers hit the wrong keys. Over the years, she noticed a pattern: How well she plays depends on her mood. A bad mood or lack of sleep almost always leads to sluggish, mistake-prone music.