Researchers at East Carolina University in the US have found that playing casual video games can reduce symptoms of depression. Over two sessions researchers measured participants on scales of depression, and using saliva samples and EEG as well. The experimental group was asked to play one of three PopCap games (PopCap provided the finances for the study), while the control group spent a half hour surfing the University's website. Participants in the experimental group were asked to continue playing the games periodically in between the two sessions.
Researchers found large reductions in elements of negative mood, including tension, anger and depression, as well as a reduction in anxiety - both in at-the-moment anxiety and overall anxiety. This effect was found both in the short-term, after having played the games for a half hour, and long-term as well, over the weeks between sessions.
Details can be found at the university's Psychophysiology Lab and Biofeedback Clinic site, which provides a PowerPoint presentation about the study, but does not indicate if this has been submitted to or accepted by a peer-reviewed journal. The authors of the PowerPoint conclude that their data suggest prescribed casual gaming may be indicated in helping reduce depression and anxiety. That being said, the study does not measure the effectiveness of gaming against the effectiveness of traditional treatments for depression, such as cognitive behavioural therapy or talk therapy combined with medication.