The good news about adopting the new habit of meditation is that it begins to revive the brain almost immediately, so that someone suffering with depression doesn’t have to wait for weeks or months to see any result. Brain scans reveal that after only four hours of meditation over several days, areas of the brain responsible for focused attention (“mindfulness”) and injured by childhood trauma, were clearly strengthened and more active. And after eleven hours, the brain tissue in those areas became more dense, thus enhancing functional capacity. The most common cause of depression—and the accompanying damage to the brain—is childhood adversity (sexual, physical or emotional abuse; witnessing abuse of one’s mother; divorce or separation; having criminal, mentally ill or addicted parents); however, meditation can virtually erase that damage.
(Start at 20:42) David Hendricks, MD and Buddhist practitioner
Meditation and Mental Health 