The experiment was conducted on a group of students that was divided into two classes. All of them had to learn English vocabulary but one group had to do it with scent defusers in the class as well as use scent defusers when they went to sleep. The scent defusers in use were essentially rose-scented incense sticks that they were asked to place on their desks while learning any by their beds as night. Another experiment also had them placing the scented stick on the desk when they were taking their exam. Incredibly, the group of students who smelled the roses did better on their test!
So how does that work?
The hippocampus is a part of the brain which stores new memories, which means it is essential that it operates well when we learn. When information is new like that, it needs to get processed in order to be stored in a different part of our brain to get logged into our long term memory. This process happens when we sleep. Scents are incredibly effective in helping us activate the hippocampus, which means that memories that are tied to certain scents are more powerful and easier to draw on command. This is why connecting the test material with a pleasant smell helped the students do better on the exam.