I recently read an article by TV's Dr Chris van Tulleken (of the Truth About...series). He was involved in a scientific study at the University of Northumbria of the effects of rosemary and lavender essential oils, specifically by inhalation.
Rosemary has long been associated with improving memory. It was found that; "there are compounds in rosemary oil that may be responsible for changes in memory performance. One of them is called 1.8-cineole - as well as smelling wonderful (if you like that sort of thing) it may act in the same way as the drugs licensed to treat dementia, causing an increase in a neurotransmitter called acetylcholine."
Lavender also had a sedating effect on volunteers. Lavender has long had an association with assisting relaxation and sleep.
The full article link; http://www.bbc.co.uk/news/magazine-33519453