What kind of advice are you looking for? You meant how to start? Just choose a country, find a list of good universities, check their website to see if they have a programme you are looking for. Then you choose an area of your research interests. Behavioral Sciences is too general. You have to think of something in particular. Read research articles,and see what is yours. When you get the idea, contact professors at universities to see if they would be interested in taking you. If all goes well, apply to these universities.