Cognitive Impairment and the Link to Sleep Apnea

Cognitive impairment is something that almost every adult suffers to some degree as they age. If you have trouble remembering things, learning, concentrating, and making decisions then you may be suffering from cognitive impairment. While this condition may seem like it goes hand in hand with aging, there actually could be another reason for a decline in your cognitive abilities.

The Connection Between Cognitive Impairment and Sleep Apnea

Studies are now linking cognitive impairment to sleep apnea. For people who suffer from the sleep disorder, this may seem disheartening. However, it’s important to realize that sleep apnea is easily treatable. In fact, many of the people who are being treated for sleep apnea have actually shown an improvement in cognitive function. This is great news for all individuals who suffer from sleep apnea and other sleeping disorders. Your cognitive impairment may improve with treatment!

Studies are showing that improving your quality of sleep may actually enhance your mental performance, according to MDedge.

David Holtzman, MD, Chair of Neurology at Washington University in St. Louis, and colleagues found that sleep deprivation raised levels of amyloid-β in the brains of vulnerable mice. “This is the same protein that tends to aggregate in Alzheimer’s disease,” said Dr. Bliwise. “It certainly is a provocative finding.”

When the researchers restricted animals’ sleep for 20 of 24 hours over 21 days, they found accumulations of amyloid-β throughout the brains. “This is fairly convincing data that sleep might be important here, particularly if an animal or human is deprived of it,” said Dr. Bliwise.

This evidence shows that impaired sleep can relate directly to cognitive impairment. Anyone who’s suffered from sleep apnea can likely confirm this on their experiences prior to treatment. However, the link between these conditions doesn’t stop there.

Cognitive Impairment and Reduced Oxygen Levels

The connection between cognitive impairment and sleep apnea goes beyond a simple lack of sleep. People who suffer from sleep apnea also tend to suffer from reduced oxygen levels as they sleep. Reduced oxygen to the brain also can impair cognitive ability. MDedge continues:

Animal studies also have suggested a link between hypoxia, which often results from sleep-disordered breathing, and cognitive impairment. Michael J. Decker, PhD, Associate Professor of Neuroscience at Georgia State University in Atlanta, subjected rat pups to several hours of intermittent hypoxia per day for four days. When he sacrificed the animals 80 days later, he found various changes in their dopamine systems, including an upregulation of their dopamine transporters. The results suggest that hypoxia can impair neurotransmitter systems, said Dr. Bliwise.

David Gozal, MD, Chair of Pediatrics at the University of Chicago School of Medicine, exposed young and old animals to 12 hours of intermittent hypoxia per day for two weeks. The elderly animals experienced much more cell death than younger animals did, which indicates that sleep apnea could hasten degeneration, according to Dr. Bliwise.

We can see how the two major problems with sleep apnea are affecting cognitive ability. Both reduced quality and duration of sleep, along with reduced oxygen levels create the perfect storm to wreak havoc on our cognitive function. But are these studies indicative of what is occurs in the brain of someone who has sleep apnea?

Brain Imaging Technology and Cognitive Impairment

Rats and mice may show cognitive impairment due to the primary issues with sleep apnea. However, is the same connection present in the more complex human brain? We now turn to brain imaging technology for a more detailed look at how sleep apnea affects the human brain.

Rachel Wynn at Gray Matter Therapy writes about obstructive sleep apnea syndrome (OSAS):

Several studies have conducted brain imaging for patients with sleep apnea. Neuroimaging included structural MRI, functional MRI, and magnetic resonance spectroscopy. In conducting neuroimaging studies researchers are trying to determine if and where sleep apnea negatively impacts the brain. Some studies reported no differences in white matter, periventicular hyperintensities, or gray matter in people with sleep apnea compared to normal subjects. However, there have been several studies that have found significant differences between the OSAS and normal subjects.

These studies have suggested OSAS correlates with decreased gray matter in the hippocampus, anterior cingulate, cerebellum, and the frontal, parietal, and temporal lobes. Other studies have revealed “decreased brain activation in the cingulate, frontal, and parietal regions during the performance of sustained attention tasks as compared with control subjects.” One study revealed gray matter loss can be reversed when the subject was compliant with sleep apnea treatment. (The current gold standard for treatment is a CPAP or continuous positive airway pressure.) After treatment significant gains were found in cognitive performance as well as a reversal in gray matter loss in the left hippocampus, left posterior parietal cortex, and right superior frontal gyrus. Could early detection and treatment of sleep apnea prevent long term cognitive impairment?

Consistency in Brain Imaging Studies

There may be some inconsistencies across the studies, but there are also common traits. Ms Wynn continues:

Consistent throughout the studies that found a difference between people with sleep apnea and normal controls was decreased hippocampal volume. Remember the hippocampus? It is very important for memory consolidation. A study looking at guinea pigs with sleep apnea revealed recurrent apnea resulted in excitotoxicity of hippocampal neurons, which results in apoptosis or cell death. We also think of the hippocampus being one of the first areas of the brain to be impacted by Alzheimer’s disease.

This information sheds light on some of the cognitive impairment that all sleep apnea patients share.

One thing is certain, the evidence we already have is undeniable. There does seem to be a link between sleep apnea and cognitive impairment to some extent. Now we just need more information to establish a solid link between the two conditions.