If I forget the name of the person who conducted a study (e.g. Harlow), is it possible to pick up full marks for explaining only the study?

The answer is yes. Generally, the person marking your paper will know the study you are on about if you provide enough detail. If you can remember the name of the person who conducted the study then that will help the examiner mark your paper with more ease. Remember, it is not necessary to remember the year a study was done. Perhaps try remembering the names of key studies if you find it difficult to remember lots of names from lots of different studies.