From Meditation Rewires the Brain:

Meditation seems to have a lasting impact on how the brain is wired, even among novices. One study found that an eight-week course in compassion meditation—in which people focus on a wish for all beings to be free from suffering—shifts brain activity in a way that usually gives a sense of well being. Studies have also shown a similar impact from mindfulness meditation, in which a person impartially contemplates whatever thoughts crop up in his or her consciousness.