You'll need to find 8-12 original research articles for your literature review. Stick to using the library databases to search for peer-reviewed articles, which you can find by checking the Scholarly (Peer-Reviewed) Journals box on your search results page.
Search by: keywords and subjects, methodology (study type), synonyms, populations
Limit by: scholarly/peer-reviewed, full text, date, available in library collection, academic journals
Check out: abstracts, subjects/keywords/author-supplied keywords, authors, references pages on relevant articles