A battery of neuropsychological tests was then used to compare the volunteers' memory, verbal learning, planning, and attention-switching skills before and after the six-month trial.

Astonishingly, there was a clear 226 percent difference between the responses provided by those who were exposed to a variety of fragrances and individuals in the control group. A scan of their brains also revealed a significant change in the anatomy linking areas of the brain critical in memory and thinking within the test group.

—  Read more in Brain Function Dramatically Boosted by Certain Fragrances During Sleep at Science Alert.