A small study involving 20 people has found that those who were exposed to 1,8-cineole, one of the main chemical components of rosemary essential oil, performed better on mental arithmetic tasks. Moreover, there was a dose-dependent relationship — higher blood concentrations of the chemical were associated with greater speed and accuracy.
Participants were given two types of test: serial subtraction and rapid visual information processing. These tests took place in a cubicle smelling of rosemary. Participants sat in the cubicle for either 4, 6, 8, or 10 minutes before taking the tests (this was in order to get a range of blood concentrations). Mood was assessed both before and after, and blood was tested at the end of the session.
While blood levels of the chemical correlated with accuracy and speed on both tasks, the effects were significant only for the mental arithmetic task.
Participants didn’t know that the scent was part of the study, and those who asked about it were told it was left over from a previous study.
There was no clear evidence that the chemical improved attention, but there was a significant association with one aspect of mood, with higher levels of the scent correlating with greater contentment. Contentment was the only aspect of mood that showed such a link.
It’s suggested that this chemical compound may affect learning through its inhibiting effect on acetylcholinesterase (an important enzyme in the development of Alzheimer's disease). Most Alzheimer’s drugs are cholinesterase inhibitors.
While this is very interesting (although obviously a larger study needs to confirm the findings), what I would like to see is the effects on more prolonged mental efforts. It’s also a little baffling to find the effect being limited to only one of these tasks, given that both involve attention and working memory. I would also like to see the rosemary-infused cubicle compared to some other pleasant smell.
Interestingly, a very recent study also suggests the importance of individual differences. A rat study compared the effects of amphetamines and caffeine on cognitive effort. First of all, giving the rats the choice of easy or hard visuospatial discriminations revealed that, as with humans, individuals could be divided into those who tended to choose difficult trials (“workers”) and those who preferred easy ones (“slackers”). (Easy trials took less effort, but earned commensurately smaller reward.)
Amphetamine, it was found, made the slackers worked harder, but made the workers take it easier. Caffeine, too, made the workers slack off, but had no effect on slackers.
The extent to which this applies to humans is of course unknown, but the idea that your attitude to cognitive effort might change how stimulants affect you is an intriguing one. And of course this is a more general reminder that factors, whatever they are, have varying effects on individuals. This is why it’s so important to have a large sample size, and why, as an individual, you can’t automatically assume that something will benefit you, whatever the research says.
But in the case of rosemary oil, I can’t see any downside! Try it out; maybe it will help.
First study: http://www.medscape.com/viewarticle/759506 (free reg reqd)
Second study: http://the-scientist.com/2012/03/28/stimulants-fail-to-stimulate/
 . Plasma 1,8-Cineole Correlates with Cognitive Performance Following Exposure to Rosemary Essential Oil Aroma. Therapeutic Advances in Psychopharmacology [Internet]. 2012 . Available from: http://tpp.sagepub.com/content/early/2012/02/24/2045125312436573 Abstract
 . Sensitivity to Cognitive Effort Mediates Psychostimulant Effects on a Novel Rodent Cost|[sol]|Benefit Decision-Making Task. Neuropsychopharmacology [Internet]. 2012 . Available from: http://www.nature.com/npp/journal/vaop/ncurrent/abs/npp201230a.html