Is your sleep apnea worse during REM or during non-REM stages of sleep? If you are like most sleep apnea sufferers, your sleep apnea is worse during REM. This can be an issue, as picking the proper pressure to treat apneas during both non-REM and REM is sometimes challenging. But does it really matter? If apnea treatment is effective during non-REM but not during REM, are those REM-only apneas actually harmful? When we take into consideration the fact that memories are transferred from short-term to long-term storage during certain stages of sleep, these apneas might really matter. Previous studies have suggested that sleep is important for memory formation – specifically visuospatial memories. These memories allow us to build a visual map of our surroundings so that we may find our way back through the same space in the future. It is unknown what specific aspects of sleep contribute to this type of memory formation. If REM does contribute to visuospatial memory formation then REM-only apneas may indeed be harmful and hazardous.
The effect of REM only apnea was investigated in an interesting way in a recent experiment that was conducted at New York University. About 20 subjects were asked to navigate through a 3D video game map before and after sleep as fast as possible. The time that each subject took to complete the maze was compared before and after sleep. This experiment was performed on each subject twice. But here’s the catch – each subject had severe, well-treated sleep apnea (treated with CPAP). On one of the two nights, the subjects were fully treated, meaning their CPAP machine was set to the appropriate pressure throughout the whole night. On the second of the two nights, CPAP was set to the appropriate pressure only during non-REM stages. Therefore, there was no CPAP treatment during REM sleep, and many apneas occurred. In this way, REM-only sleep apnea was induced. If performance after sleep without CPAP was poorer than performance with CPAP, this would indicate that REM disruption had affected memory formation.
Results showed, as expected, that learning was affected by REM-only sleep apnea. The participants performed much, much worse after a night of REM-only apnea than they did when they had an intact night of sleep. Importantly, sleepiness levels were compared (via a reaction time test) between the two mornings to ensure that heightened sleepiness levels that may have occurred as a result of REM disruption did not affect the results. Sleepiness levels between the two mornings were not different, indicating that it was, in fact, the REM disruption that caused the learning deficits.
These results suggest that apneas during the REM stage of sleep may be detrimental for learning. Given that many people have untreated apnea or their apnea treatments are not perfectly effective during REM sleep, this is an important finding. If treatment is not effective during REM, there are alternative treatment options. For example, there have been certain modifications to CPAP that allow pressure changes throughout the night. If these machines sense that the sleeper has entered REM, the pressure ramps up so that treatment may be more effective. Or perhaps having a higher pressure throughout the whole night is the better option. Luckily, a full overnight sleep study will reveal if sleep apnea is more severe in REM, so ask your sleep physician!
Apnea-Induced Rapid Eye Movement Sleep Disruption Impairs Human Spatial Navigational Memory: Journal of Neuroscience – pre-publication.