Smelling a strong fragrance during sleep offers a major boost to memory and could be a potential treatment for dementia, a study has found.
Researchers in the US found that leaving a fragrance wafting through the bedroom of older adults for two hours every night for six months boosted cognitive capacity by 226 per cent.
For the trial, a group of men and women aged 60 to 85 were given a diffuser and seven cartridges, each containing a single and different natural oil. One group received full-strength cartridges, while the other was given the oils in tiny amounts.
Participants put a different cartridge into their diffuser each evening prior to going to bed, and it activated for two hours as they slept.
The group who received full-strength cartridges reported a 226 per cent increase in cognitive performance compared to the control group.
Scientists assessed their cognitive performance using a word list test commonly used to evaluate memory.
Imaging also revealed better integrity in a part of the brain called the left uncinate fasciculus, which becomes less robust with age. Participants also reported sleeping more soundly.
The loss of smell, known in science as the olfactory sense, is traditionally seen as a precursor to developing neurological and psychiatric diseases, including Alzheimer’s and Parkinson’s.
The study was conducted by the University of California, Irvine’s (UCI) Centre for Neurobiology of Learning and Memory.
Michael Yassa, a professor in neurobiology and the director of the centre, said: “The olfactory sense has the special privilege of being directly connected to the brain's memory circuits.
“All the other senses are routed first through the thalamus. Everyone has experienced how powerful aromas are in evoking recollections, even from very long ago.
“However, unlike with vision changes that we treat with glasses and hearing aids for hearing impairment, there has been no intervention for the loss of smell.”
The researchers said they hoped the findings would lead to more investigations into smell therapies for memory impairment.
Researchers have previously found that exposing people with moderate dementia to up to 40 different odours twice a day over a period of time boosted their memories and language skills and eased depression.
The study's first author, project scientist Cynthia Woo, said scientists reduced the number of scents to seven rather than use multiple aromas, as previous studies have done.
“By making it possible for people to experience the odors while sleeping, we eliminated the need to set aside time for this during waking hours every day.”
Michael Leon, professor of neurobiology and behaviour and a CNLM fellow, said: “The reality is that over the age of 60, the olfactory sense and cognition starts to fall off a cliff.
“But it's not realistic to think people with cognitive impairment could open, sniff and close 80 odorant bottles daily. This would be difficult even for those without dementia.”
The team's study was published in the journal Frontiers in Neuroscience.
