Scientists examine what goes on inside our brains when we dream and find surprising connections with neurodegenerative disorders.
Research presented at the 2017 annual gathering of the Canadian Association for Neuroscience, held in Montreal, investigates what goes on inside our brains when we dream. Surprisingly, the research also suggests that dream dysfunctions may predict the development of neurological disorders such as Parkinson's disease or dementia.
The research was conducted by Dr. John Peever and his team at the University of Toronto in Canada in 2015.
Dr. Peever and colleagues have previously studied how dreams occur and discovered the brain cells that are responsible for reaching the dream state: the so-called REM-active neurons.
How do we dream?
Since the 1960s, scientists have known that dreaming occurs during rapid eye movement (REM) sleep, and that the brainstem is a key brain region responsible for controlling dreams.
The brainstem is located at the base of the brain, and it communicates with the hypothalamus to transition from wakefulness to sleep, and vice versa. A chain reaction started by REM-active "SubC" neurons ultimately releases the GABA neurotransmitter, which, in turn, reduces the level of arousal in the hypothalamus and the brainstem. SubC neurons take their name from the brain area in which they are found: the subcoeruleus nucleus.
These brain cells that produce GABA, or GABAergic neurons, control the timing of REM sleep and its features, such as muscle paralysis. As Dr. Peever explains, "When we switch on these cells, it causes a rapid transition into REM sleep." The brainstem sends signals to relax muscles and limbs so that we do not do in real life what we dream about while asleep.
People with narcolepsy do not just fall asleep instantly, but they also experience cataplexy, which is the sudden loss of muscle tone while they are awake.
REM sleep disorders linked to neurodegenerative conditions
While examining the breakdowns in the brain circuits that cause these disorders, the team made an interesting discovery.
They found that REM sleep disorders are linked to several neurodegenerative diseases that tend to occur in old age. "This link suggests that neurodegenerative processes initially target the circuits controlling REM sleep and specifically SubC neurons," write Dr. Peever and colleagues in their 2015 paper.
"We observed that more than 80 percent of people who suffer from REM sleep disorder eventually develop synucleinopathies, such as Parkinson's disease, and Lewy body dementia. Our research suggests sleep disorders may be an early warning sign for diseases that may appear some 15 years later in life."
Dr. John Peever
The National Institutes of Health (NIH) estimate that approximately 50,000 people in the United States are diagnosed with Parkinson's disease every year, and around half a million people live with the disease. Lewy body dementia affects another 1 million U.S. adults.
Both Parkinson's disease and Lewy body dementia are characterized by a buildup of a neuronal protein called alpha-synuclein inside the neurons.
In the future, Dr. Peever hopes that his research will pave the way for neuroprotective therapies that would prevent against the development of such neurodegenerative disorders.
"Much like we see in people prone to cancer, diagnosing REM disorders may allow us to provide individuals with preventative actions to keep them healthy long before they develop these more serious neurological conditions," Dr. Peever says.