Video from the folks in the Kimbel Library at Coastal Carolina University explaining the difference between Popular and Scholarly sources.
The WebMD article linked above uses language that tells you it is not the original study but discussing research someone else has conducted:
The study WebMD is discussing is a scholarly source, but the WebMD article itself is not. It is a secondary source - one that summarizes original research. The article includes some publishing information about the original study that will help you find the research article.
From the WebMD article:
Use the information provided as search terms to find for the original study: Proceedings of the National Academy of Sciences, November 3, 2014, Wig, brain and memory. This is available online (use the Journal Finder to see if it is available in a library database).
*There is nothing 'wrong' with the WebMD article, it is just not appropriate for this assignment.
Note the language in the research study that informs you that it is original research:
These phrases show the reader that the authors of the article are the same ones who conducted the study and are presenting their original research. Original research articles are often referred to as Scholarly, Peer-Reviewed or Professional sources. These articles will often begin with a background section summarizing previous research on the topic, but most of the article will be about the original study.