New research from NYU Langone Medical Center in New York indicates that sense of smell has a complex relationship with memory accuracy. Indeed, the researchers find that memory of smell relies on how the brain works during slow-wave sleep.
So researchers believe that a better understanding of how the brain processes odors could lead to innovations in improving memory for patients with neurodegenerative disorders.
To examine this, the NYU researchers devised experiments to show how rats respond to odor memory.
By stimulating different smell perceptions in the rats using electrodes in the brain region that processes smells - the olfactory bulb - the researchers trained the rats to recognize different odors.
Each "odor" was distinguished by precise patterns of electrical stimulation. While the rats were asleep, it was then possible for the researchers to investigate the interactions of odor memory with slow-wave sleep - a kind of deep sleep involving slow brain waves.
Memories of odors were 'enhanced' during slow-wave sleep
The researchers found that replaying the electrical odors to the rats during slow-wave sleep "enhanced" the memory of these odors.
By contrast, when the electrical odors were replayed to the rats while they were awake, there was a decrease in the strength of the memory, similar to rats who received no replay of the learned odor.
Fast facts about slow-wave sleep
- Slow-wave sleep occurs over the first hour of sleep, during which the brain waves slow down.
- Heart rate, blood pressure and body temperature all fall during slow-wave sleep.
- If someone is awakened during slow-wave sleep, they may recall fragmented thoughts but not active dreams.
The rats were also easily confused if a false pattern - that they had never learned - was incorporated into the playback. The rats were unable to discriminate between the learned smell and the false pattern - they had false memories.
Using drugs to prevent the neurons in the brains of the rats from communicating with each other during sleep also reduced the accuracy of the odor memory.
Senior author Dr. Donald Wilson considers his team's findings to be the first to demonstrate that memory accuracy is altered during slow-wave sleep.
"Our findings confirm the importance of brain activity during sleep for both memory strength and accuracy," says Dr. Wilson.
"What we think is happening is that during slow-wave sleep, neurons in the brain communicate with each other, and in doing so, strengthen their connections, permitting storage of specific information."
Dr. Wilson, who publishes his findings in the Journal of Neuroscience, plans to research how memory and perception are affected by sleep disorders.Last year, Medical News Today reported on another study from the Journal of Neuroscience that found how well people are able to perform specific motor tasks - such as typing or playing the piano - is influenced by how much slow-wave sleep they get.