Sleeping at night with just two hours of diffused scent tripled memory strength and induced neurogenesis in the brain’s learning centre, discovered scientists at the University of California, Irvine, (UCI). They also saw improved functioning of an area of the brain linked to memory and cognition which typically declines with age. Participants included a group of people with moderate dementia.
It’s known that one of the early signs of Alzheimer’s is losing a sense of smell. And olfactory dysfunction (the loss of ability to smell) is also found in virtually all neurological and psychiatric disorders. ‘I’ve counted 68 of them,’ said UCI Senior Investigator, Dr Leon, ‘including anorexia, anxiety, attention deficit/hyperactivity disorder, depression, epilepsy, and strokes. In fact, by mid-life, your all-cause mortality can be predicted by your ability to smell things.’
An earlier experiment by researchers at the University of California Irvine, investigating autism, had found that exposure to individual essential oils for 30 minutes a day over three months induced neurogenesis in the olfactory bulb and the hippocampus. The hippocampus is important as it has a major role in learning and memory.
The olfactory system is the only sense that has a direct ‘superhighway’ input to the memory centre areas of the brain. All the other senses have to reach those brain areas through what might be called the ‘side streets’ of the brain, and so consequently, they have much less impact on maintaining the health of those memory centres.
In a later small, randomized control trial they found that when cognitively normal individuals were exposed to the scent of an essential oil for two hours every night over 6 months, they experienced a 226% improvement in memory compared with a control group who received only a trace amount of the diffused scent.
In addition, functional magnetic resonance imaging (fMRI) showed that those in the enriched group had improved functioning of the left uncinate fasciculus, an area of the brain linked to memory and cognition, which typically declines with age.
Dr Michael Leon told Medscape News, ‘To my knowledge, that level of [memory] improvement is far greater than anything that has been reported for healthy older adults and we also found a critical memory pathway in their brains improved to a similar extent relative to unenriched older adults.’
When olfaction is compromised, “the memory centres of the brain start to deteriorate and, conversely, when people are given olfactory enrichment, their memory areas become larger and more functional,” he added.
For the study, researchers randomly assigned 43 older adults, aged 60 – 85 years, to receive either nightly exposure to essential oil scents delivered via a diffuser (n = 20; mean [SD] age, 70.1 [6.6] years) or, for the control group, a diffuser with only trace amounts of odorants (n = 23; mean age, 69.2 [7.1] years) for a period of 6 months.
Olfactory stimulation not only restores olfactory function, according to the study published online in Frontiers of Neuroscience, it also improved brain anatomy by stimulating neurogenesis, the growth of new neurones.