What causes pulsing in the vaginal area?

It's unclear what type of pulsing you are inquiring about.  There is definitely a pulsing of the muscles that surround the opening of the vagina at the time of orgasm.  Also, some women feels pulsing or tingling in their vagina when they get aroused, which is perfectly normal.   This happens because there is increased blood flow to the area and the muscles of the vaginal wall may have some minor contractions.  The vagina also has arteries that supply blood to the area, and it is possible in some women to feel their pulse in certain spots.