Last Fall, when I was taking my intervention specialist classes, I learned in my Sensory Integration class that certain scents stimulate the brain. I went on a spontaneous shopping spree a couple days ago and came across those scented oil reed dispensers. I got on my phone and started researching specific scents that affect learning.
(Click picture to go straight to "Smell Sense" on Accelerated Learning Methods)
I also found a PDF of a research paper titled The Effect of Pleasant Fragrances on Student Behavior in a Kindergarten Classroom