The ability to remember locations and directions may suffer when deep sleep is disrupted by breathing difficulties, a new study suggests.
Sleep apnoea affects spatial memory
People with sleep apnoea tended to score worse on spatial memory tests after sleeping without their breathing aid, compared to mornings after they'd used their breathing aids at night, researchers found.
"There had been some evidence in animal models that REM sleep or dreaming sleep is important for spatial memory, but no one had shown or proven that in people," said Dr. Andrew Varga, the study's lead author from NYU Langone Medical Centre in New York City.
"Spatial memory" helps people remember how to get to their children's schools, or where they left their keys, for example.
It's thought that people may have difficulty forming new spatial memories if their deep sleep and shallow sleep are interrupted, according to Varga.
People with sleep apnoea - some 18 million Americans, according to the National Sleep Foundation - experience numerous pauses in breathing that can last from seconds to minutes. As a result, people with sleep apnoea are often tired when they wake.
CPAP and memory problems
To see whether individuals with sleep apnoea tended to have more difficulty forming new spatial memories, the researchers recruited 18 such people to spend two nights in their sleep centre, about two weeks apart.
The volunteers had always slept with a so-called CPAP machine to eliminate sleep apnoea. During one night in the sleep lab, they slept with CPAP. The other night, their CPAP was reduced or turned off during deep sleep to induce apnoea.
On each of the two nights, before they went to bed, participants were asked to complete a video game maze. The next morning, they completed the maze again.
After a night of sleep with their CPAP machine, the time it took the volunteers to complete the maze improved by about 30 percent. They also travelled farther in the maze and spent less time backtracking.
But after a night with sleep apnoea, the volunteers were about 4 percent slower at completing the maze, compared to the night before.
"People had no improvement and actually on average they got a bit worse," Varga said. "We interpret that to mean their consolidation in spatial memory wasn't as good when REM (deep) sleep was disrupted."
Apnoea or oxygen affects spatial memory?
The researchers can't say whether the worse performance is directly from the disruptions in sleep caused by the apnoea, or whether it's the lack of oxygen the condition causes.
Varga said they are testing the apnoea or oxygen question now. They are also looking at whether apnoea during shallow sleep affects spatial memory.
"The thought is that you need both (deep and shallow sleep)," he said. "If you don't have one or the other, you don't' have the ability to consolidate the information."
Varga said he hopes the results of the study, published in The Journal of Neuroscience, will encourage more doctors to treat sleep apnoea early - instead of waiting until the condition worsens.
"Apnoea is very common and has a variety of deleterious effects that have to do not only with cardiovascular health, but also there is an emerging dataset - of which this paper is only one piece - to suggest there are really cognitive effects also," he said.
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