Sleep apnea is a sleep disorder that is estimated to impact over 18 million Americans. It is often diagnosed as a result of either chronic daytime fatigue or the reports of loud and disruptive snoring by a sleep partner, and it is the result of a narrowing an blockage of the airway as the tissues of the throat relax during sleep. It has been linked to a number of chronic health conditions as well as cognitive impairments and even an increased incidence of serious accidents. Now a study by researchers at the NYU Langone Medical Center is indicating that the condition may have a direct impact on the spatial memory capacity that is critical to every day functioning.
The study was just published in the most recent edition of the Journal of Neuroscience. The sleep specialists detail the results of having participants play a video game in order to measure memory. The play took place following a disruption of rapid eye movement (REM) sleep that is a result of sleep apnea. Based on the study, the scientists were able to prove that even in cases where the other normal sleep cycles take place in adequate quantities, the lack of REM sleep impairs special memory.
The spatial memory is notably what is first lost in patients who have been diagnosed with Alzheimer’s disease. It is why they are so often reportedly lost or found wandering around a neighborhood – it is what allows you to remember where you live, where you put your car keys, how to get to familiar locations such as work or the supermarket.
The sleep scientists from NYU had previously run similar tests on laboratory animals and had demonstrated that the loss of REM sleep affected their ability to remember. This study, led by Andrew Varga, MD, PhD, clinical instructor of Medicine in the Division of Pulmonary, Critical Care and Sleep Medicine at NYU Langone (and also an attending physician in NYU’s Sleep Disorders Center), is the first of its kind that specifically links REM sleep to spatial memory in humans and to provide an answer as to what the actual impact of that sleep deprivation is. According to Dr. Varga, “We’ve shown for the first time that sleep apnea, an increasingly common medical condition, might negatively impact formation of certain memories, even when the apnea is limited to REM sleep. Our findings suggest memory loss might be an additional symptom for clinicians to screen for in their patients with sleep apnea.”
Sleep apnea is very much in the news recently, as more and more attention is being paid to the potentially devastating impact that this chronic condition can have on health and wellbeing. People who suffer from sleep apnea are known to snore extremely loudly and in a particular characteristic way – they often notably stop breathing for an extended period of time, then suddenly snort and gasp as their brain awakens the body in a panic for the oxygen that it needs. Though the person suffering from obstructive sleep apnea is only aware of their condition through their fatigue the next day, witnesses to these events find them very disruptive, and they can occur several hundred times per night.
Although sleep apnea can occur during every stage of the sleep cycle, the episodes are often far more pronounced during REM sleep because it is then that the muscle tone in the body is most relaxed and the airway is most completely blocked. Because of this, some people only experience apnea episodes during REM sleep. Sleep researchers have focused the majority of their studies on the impact that these bouts without oxygen put on the cardiovascular system, but this study raises concerns about the impact of apnea on specific cognitive abilities.
In order to measure the specific effect that REM sleep apnea had, Dr. Varga and his fellow researchers identified 18 people who had already been diagnosed with severe sleep apnea and who were already being treated via continuous positive airway pressure (CPAP) devices. These participants were asked to spend two separate evenings in the NYU Sleep Disorders Center sleep lab. During their stay they were asked to play video games prior to going to sleep and after waking up.
The participants were tested on their use of the video game before any sleep observation took place. Using a joystick they navigated through spatial mazes. One one of their nights in the lab they were allowed to use CPAP in the same way that they had been doing at home, and on the other night their CPAP therapy was turned down during REM sleep so that they would suffer bouts of apnea. What the researchers found was that when the participants slept with the addition of CPAP therapy, their maze completion time improved by 30%, but when CPAP was turned down during REM sleep their performance dropped by 4%. Importantly, it was also determined that the sleep apnea that took place during REM sleep did not have a negative impact on reaction times. The scientists conducted what is known as a psychomotor vigilance test, which measures delayed reaction time. This is an indication that the reduced abilities on the video game test were not a result of sleepiness or lack of attention, but instead were caused by a decline in spatial memory.
Dr. Varga and his coauthors plan to design future studies in which they will try to identify the way that each aspect of sleep apnea, through individual phases of sleep, impact spatial memory.