In that previous studies have shown that yoga and other forms of exercise have beneficial effects on mood and anxiety, a team from Boston University School of Medicine (Massachusetts, USA) studied the specific biochemical changes lending these positive results. Chris C. Streeter and colleagues recruited two groups of healthy men and women for a 12-week long study.   One group practiced yoga three times a week for one hour, while the remaining subjects walked for the same period of time. The team employed brain scans to assess the levels of gamma-aminobutyric acid (GABA) activity in the subjects’ brains, and conducted surveys of psychological states at several points through the study period.  The researchers found that those subjects who practiced yoga reported a more significant decrease in anxiety and greater improvements in mood than those who walked, and brain scans showed corresponding gains in brain GABA levels.   Explaining that GABA activity is often reduced in mood and anxiety disorders, the team  writes that: “This is the first study to demonstrate that increased thalamic GABA levels are associated with improved mood and decreased anxiety. It is also the first time that a behavioral intervention (i.e., yoga postures) has been associated with a positive correlation between acute increases in thalamic GABA levels and improvements in mood and anxiety scales.”