Psychology, Health Science, Pre-OT, and Exercise Science are the most common majors. You really can major in anything you would like - as long as you take the prerequisite courses required for admissions into a graduate program. It doesn't make a difference to admissions committees which major you choose, but it may save you time and money if you choose a major which includes those courses. If you are interested in studying something unrelated, another option would be to pick up a minor if your school has one that aligns with the prerequisite courses.