It is the right brain. When you communicate with the "dead", use a crystal ball or a Ouija board, or do a seance, your right brain is sending messages. If done right, it is about as useful as having a dream, which is similar to the above.
There are other forms of spiritism. Astrology, numerology, and Tarot cards use specific markers that are supposed to stand for certain aspects of one's life. Be it the numbers that come up, the position of the planets relative to each other and the sun and where they were when you were born, cards, or tea leaves, it is supposed to have some connection to what is coming in your life. Usually, the rules are quite complex and quite meaningless.
My advice: If you are going to practice spiritism and fortune telling, or use it on yourself, treat it as entertainment. The messages are no more significant than dreaming. You might get some insight on a situation, but 90% of the time it will be inaccurate. It is best looked at as fun.