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In this study, the yoga intervention was associated with greater improvements in mood and decreases in anxiety in the tonic, acute and intervention analyses compared to the metabolically matched walking intervention, suggesting that the effect of yoga on mood and anxiety is not solely due to the metabolic demands of the activity. In our prior study, significant acute increases in brain GABA levels immediately after a yoga session were recorded. The current study found near-significant acute increases, but stable tonic levels during the 12-week yoga intervention. These observations are consistent with a time-limited effect of the yoga intervention on thalamic GABA levels.

The lack of tonic changes in this study, and the lack of baseline differences between the experienced yoga practitioners and controls in the prior study, suggest that tonic GABA levels are stable in subjects screened to exclude low GABA states. The whole group analysis of the correlations between mood and anxiety scales taken before each scan and the GABA levels obtained from those scans demonstrated significant positive correlations with the positive scales of Tranquility and Revitalization and a negative correlation with the STAI-State. To our knowledge, this is the first study to report a positive correlation between thalamic GABA levels and improved mood or decreased anxiety. The correlations between group changes in mood and anxiety scores and changes in GABA levels in the tonic and acute conditions suggest that increases in thalamic GABA levels are associated with improved mood and decreased anxiety.

This is the first study to show that a behavioral intervention (i.e., yoga) is associated with a positive correlation between changes in thalamic GABA levels and improvements in mood and anxiety. The use of METs controlled for metabolic demands of each intervention and allowed the activity level of the 2 groups (outside of the intervention) to be compared. The significantly greater level of physical activity outside the intervention in the walking group compared to the yoga group was not expected. The higher level of outside activity in the walking group could have contributed to the finding of smaller changes in mood and anxiety in the walking group, as the intervention may not have been a great enough physical challenge given the greater level of outside activity.