What Wakes You? The Brain Responds When Oxygen Levels are Low
Lead author Clifford Saper, chair of neurology at Harvard Medical School and colleagues at Beth Israel Deaconess Medical Center, found a brainstem area that senses oxygen dips and forces one to wake up.
By Nikki Tucker
Obstructive sleep apnea occurs when one's sleep is disturbed because of blockage of the airways during sleep. It affects nearly 12 million American adults. For years researchers have been intrigued to discover how one's brain knows when to wake you once breathing has stopped, new evidence can now solve this mystery.
During sleep apnea, rapid eye movement (REM) sleep paralyzes the body, which inhibits one from enacting dreams, but it may also block the airways of people.
Lead author Clifford Saper, chair of neurology at Harvard Medical School and colleagues at Beth Israel Deaconess Medical Center, found a brainstem area that senses oxygen dips and forces one to wake up. This brainstem area is known as the parabracheal nucleus (PBN). The study revealed the PBN region awakens the brain using the excitatory neurotransmitter glutamate and silences it with the inhibitory neutotransmitter GABA, released by the ventrolateral preoptic area (VLPO).
The study stimulated sleep apnea in mice with the help of a special gas chamber, where levels of oxygen and carbon dioxide could be manipulated. Once carbon dioxide was increased and oxygen was reduced for 30 seconds, healthy mice would awaken from sleep instantly, similar to humans who suffer from sleep apnea when they stop breathing. The mice that were genetically modified to silence there PBN failed to wake up between 30 and 40 percent of the time. The mice that did wake up took two to three times longer than the healthy mice, demonstrating their mechanism for fast detection of oxygen and carbon dioxide level was broken.
According to Saper, results demonstrated that the PBN is essential for the sleep-wake function. It also is responsible for danger signals, including oxygen loss, which it relays to the brain by alerting the arousal alarm.
With more research involving the structure of the brain regarding sleep, wake, and apnea may one day assist with generating medications for those suffering from insomnia and sleep-disordered breathing.
Clifford Saper presented this study at the Sleep 2012, 26th annual meeting of the Associated Professional Sleep Societies.
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