An Electroencephalogram (EEG) is a cap with electrodes that is placed on the head that record brain waves. While this data does not indicate where in the brain a process is occurring, it indicates when a process is occurring. These time sensitive waves allow scientists to further understand cognitive processes.
Multiple EEG studies were used to investigate the effects of yoga on brain waves. Desai et al. (cited below) completed a review of these studies, which together help explain the decrease of anxiety and the increase of focus experienced after yoga.
In breathing, meditation, and asana (movement, pose based) yoga practice, an increase in both the amplitude and frequency of alpha waves was found. Alpha waves are associated with the calmness an individual is perceiving.
During and after breathing based yoga sessions, beta waves produce an increase in both frequency and amplitude. Beta waves are commonly associated with performance level on tasks.
Lastly, the activity of theta waves improved during asana and breathing based yoga. Theta waves are prevalent during repetitive and autonomous tasks.
The activity of brainwaves were also correlated with improved moods, focus, and well-being. These studies show improved brainwave activity caused by yoga. Specifically, the brainwaves found are associated wit improvement in mood, cognition, memory, and anxiety.
All information provided here was found in the following study: Desai, Tailor, and Bhatt, 2015