Sleep Disorder May Be Affecting Your Memory
By DR. ANDREW VARGA
Much is known about sleep apnea's negative effects on cardiovascular health, but now evidence is building that the condition might also affect memory.
Our new study, published October 29, 2014, in the Journal of Neuroscience, demonstrated that specific disruption of rapid eye movement (REM) sleep as a result of sleep apnea may impair a person's spatial memory.
Spatial memory is utilized for everyday tasks, such as remembering the location of a favorite new restaurant, how to get home if you're forced to take a detour or where you left your keys at home.
Sleep apnea is an increasingly common medical condition that affects an estimated 4 percent of the United States population and as many as 25 percent of middle-age men. About half of those with the sleep apnea are overweight.
Sleep apnea significantly increases risk for high blood pressure, metabolic syndrome, diabetes, stroke and heart failure. But far less is known about the cognitive effects of sleep apnea.
Previously, animal studies have shown impairment of REM sleep has detrimental effects on memory. Our study, however, is the first to document the negative spatial memory consequences of sleep apnea in people.
We determined these findings by testing 18 people who have severe sleep apnea and are fully treated by sleeping with a continuous positive airway pressure (CPAP) machine every night.
Participants spent two different nights in our sleep lab and each night played a video game before they went to bed and after they woke up. In the video game, subjects used a joystick to navigate through one of two unique, computer-generated 3-D spatial mazes.
During one night's sleep, subjects used their CPAP machine throughout the night as they normally would at home. On the other night, CPAP was reduced only in the REM stage of sleep to induce sleep apnea. CPAP was maintained at the therapeutic level during all other stages of sleep.
When sleep apnea was induced during REM sleep, subjects took longer, covered more distance and spent more distance backtracking in the maze after sleep than when REM sleep was not interrupted. Specifically, when sleep was aided by therapeutic CPAP all night, we saw a 30 percent overnight improvement in maze completion time when participants played the video game the next morning. However, when REM sleep was disrupted by sleep apnea, there was no improvement and subjects took 4 percent longer to complete the maze tests.
We performed other tests to rule out that sleepiness or lack of attention were reasons for the decline in maze performance after sleep apnea was induced.
Then what about sleep apnea affects spatial memory?
Sleep apnea is thought to have two main consequences that mediate most of its detrimental effects: First, sleep apnea creates numerous repetitive dips in the oxygen levels in the blood. Second, sleep apnea creates numerous small arousals that interrupt sleep continuity.
Although sleep apnea can occur during any stage of sleep, apnea is often worst during REM sleep because of reduced muscle tone in the upper airway that naturally occurs during this stage. Some individuals, in fact, have apnea that only occurs in REM sleep.
In the meantime, if you or a loved one suspects they have sleep apnea, find a trained sleep specialist for an evaluation.
Readers -- Do you have trouble sleeping or getting enough sleep? Do you or anyone you know suffer from sleep apnea? When you don't get enough sleep, does it affect your performance the following day? Leave a comment below and let us know.
Dr. Andrew Varga, Ph.D., is a clinical instructor of Medicine in the Division of Pulmonary, Critical Care and Sleep Medicine at NYU Langone Medical Center. He earned a Ph.D. in neuroscience and is an attending physician at NYU Sleep Disorders Center and is board-certified in both neurology and sleep medicine.
Dr. Varga has a longstanding interest in mechanisms of learning and memory and the role of sleep in memory consolidation. He has an active research program both on the systems level in human subjects and on the molecular level, and his clinical interests involve all areas of sleep medicine with particular interest in movement disorders in sleep (RLS, REM Behavior Disorder), sleep in neurodegenerative diseases (such as Alzheimer's disease and Parkinson's disease) and generalized cognitive deficits as a function of fragmented sleep.