Most people are familiar with some of the symptoms of sleep apnea: daytime fatigue or tiredness, morning headaches, restlessness during the night, and just an overall sense of waking up feeling unrefreshed. What is less known, however, is how sleep apnea—particularly severe sleep apnea that is often accompanied by frequent and significant drops in oxygen levels—may actually affect the brain’s physical structure, thereby changing how effectively it can function. A new study published in the January 2012 edition of the sleep medicine journal SLEEP examines how sleep apnea may affect the brain by comparing neuroimaging of the brain before and after treatment with continuous positive airway pressure (CPAP).
Brain Damage: Permanent or Reversible?
Using neuro-imaging techniques, the researchers evaluated the metabolism rates of different brain areas in thirty participants with untreated severe sleep apnea, compared to twenty-five normal subjects who were used as a control group. They found that the white matter in the frontal lobe of the brain and the hippocampus showed abnormal metabolism levels. Neurocognitive tests were given to both groups to assess brain functioning. Interestingly, poor results were not significantly correlated with the abnormal metabolism concentrations, but were strongly correlated with the severity of the participant’s sleep apnea.
Twenty-seven of the participants with severe sleep apnea were then placed on CPAP therapy. These subjects were retested (both neuroimaging and neurocognitive tests) after six months of treatment. Abnormal metabolism levels were still found in the white matter of the frontal lobe, but metabolism rates in the hippocampus had become normal. While participants’ mood and quality of life had improved following CPAP treatment, only one of the test scores (a color association task) was significantly improved—the others remained the same.
The results of the study suggest that damage to the white matter of the frontal lobe in the brain because of severe sleep apnea may be permanent, but inflammation of the hippocampus may be improved with CPAP.
What Do the White Matter and the Hippocampus Do?
The cells in the white matter of the brain are involved in a variety of functions. Perhaps the most important of these is the relay of sensory information (sights, sounds, smells, touch) from body to the cerebral cortex. Other cells are involved in the regulation of some of the body’s automatic processes, such as maintaining an appropriate body temperature, blood pressure, and heart rate. Sleep apnea is known to be significantly correlated with unhealthy changes in blood pressure (and in some cases, heart rate); perhaps the destruction of the white matter plays a role in this process.
The hippocampus is primarily involved in the formation and storage of new memories, as well as tying them to those stored in long-term memory. Because the inflammation of the hippocampus due to severe sleep apnea is improved with CPAP, this may explain why some people suffering from memory deficits find their memory improved after starting CPAP therapy for sleep apnea.