Why Do PTSD Patients Relive Intense Fear-Based Memories In Sleep? New Models Provide Insight.
Many people who suffer from post-traumatic stress disorder often relive highly-charged fearful and emotional memories while they sleep, and neuroscientists from Virginia Tech have recently discovered what is behind this phenomenon using models of the brain, the news outlet for Virginia Tech reported. The findings provide vital information for creating therapies that could mitigate the effects PTSD has on sleep.
The brain can be very active during rapid eye movement (REM) sleep, so much so that Virginia Tech neuroscientist, professor, and co-author of the study, Sujith Vijayan called it “paradoxical sleep.” Combining the high activity of REM sleep with post-traumatic stress disorder, people who suffer from the disorder can relive painful memories “over and over” again, according to Vijayan.
Normally, the brain can bring up emotional memories during REM sleep to cleanse the emotional charge. However, this normal process can malfunction for people who suffer from PTSD, and the result is that painful memories come to mind night after night.
In their study, published in The Journal of Neuroscience, Vijayan and his team of researchers constructed a biophysical model of the brain where they could simulate neurophysiological functions like communication between different parts of the brain, neurotransmitters, and brain waves.
By adjusting the brain rhythms between the prefrontal cortex and the amygdala in the model, researchers were able to link lower levels of the neurotransmitters norepinephrine and serotonin with the brain’s ability to restrain fear and pain-based memories during REM sleep. They further found that those who suffer from PTSD experienced high levels of norepinephrine and serotonin during REM sleep, thus repeatedly causing painful memories to come to mind.
Other studies have shown that the emotional charge of negative memories is mitigated by REM sleep. However, it is still the “wild west” when it comes to understanding how REM sleep works, Vijayan described. “REM sleep is a lot harder to get your hands around. There are really good models out there for how non-REM sleep might consolidate memories and what role it might play in learning and memory. But when we talk about REM, there are no real, good models on how that stuff is happening,” he said.
So, this new model from Vijayan and his team provides quite the insight. Looking at brain wave rhythms between the prefrontal cortex and the amygdala, they found that four to eight hertz on the theta range of brain rhythm, which is common for humans, allowed for the greatest strength of communication in the brain. This, in turn, inhibits fear expression cells during sleep.
When researchers adjusted the models to include high levels of norepinephrine and serotonin during REM, four to eight hertz on the theta range of brain rhythm was ineffective at inhibiting fear expression cells. But, they did find that ten hertz was effective at suppressing fear expression cells in the PTSD brain model.
Therapies could be created as a result of the findings, namely covert auditory stimulation, as Vijayan calls it. “That means I’m playing those sounds and you’re not aware of it while you’re sleeping,” he said. “That could be useful for any sort of disorder where sleep is disrupted, not only in PTSD, but in traumatic brain injury or Parkinson’s disease. The idea is that by inducing desired neural dynamics, we can engage the recuperative powers of sleep.”
