You do not need to apply to be admitted to the undergraduate programs in psychology or neuroscience at Indiana University. The only requirements are that you’ve been admitted to the university and have been certified by the College of Arts and Sciences, a process that happens for most students at the end of their first year.
If you take the introductory course for the major, find it interesting and earn a good grade, then you're likely to enjoy and do well in upper-level classes. Explore your options with an academic advisor as you plan your undergraduate career.