Feelings of happiness and sadness are central to conscious experience, but we still know little about what happens in the brain when we have these feelings or how these feelings relate to the events in our lives. My lab's research combines computational modeling with neuroimaging to study the relationship between decision making and emotion across the lifespan and in people with depression. I developed a mathematical equation for happiness that explains the role that expectations have in how we feel. My lab has developed a smartphone app called The Happiness Project so that anyone can contribute to our happiness research. Download The Happiness Project (https://thehappinessproject.app) and play games for science!