The following informative page answers questions on how the brain responds to Sahaja meditation. It's calming effect can be seen from the brain activation patters observed via EEG. Here is an extract. Go here for the full article.
Electrophysiological studies (EEG) measure the electrical activity from groups of neurons on the surface of the scalp. EEG studies comparing the brain activation of long-term Sahaja Yoga practitioners (11) to short-term Sahaja Yoga meditators (16) found specific brain activation patterns corresponding to the subjective feelings of thoughtless awareness and happiness experienced by the Meditators (Aftanas and Golocheikine, 2001, 2002, 2000). In their EEG measures, the long-term meditators showed increased power in low band frequency EEG activity of theta and alpha, which was particularly pronounced over the left frontal regions.