Neuroscientists finally know why PTSD patients have recurring nightmares

BLACKSBURG, Va. — Sleep can bring out emotions that typically stay inside of us — sometimes in the form of nightmares. For those with post-traumatic sleep disorder, the brain tends to make bad memories come back night after night among people with PTSD. Now, Virginia Tech researchers say they know why post-traumatic stress disorder patients keep reliving these disturbing incidents in their sleep.

Researchers note that post-traumatic sleep disorder keeps the brain and those experiencing this nightly trauma stuck in a vicious cycle. During rapid eye movement (REM) sleep, brain activity is elevated, which can lead to the brain exhibiting behavior similar to when people are awake. In fact, the brain can even be more awake during REM sleep than when you’re actually up, which is how it got its nickname of “paradoxical sleep,” according to Virginia Tech neuroscientist Sujith Vijayan.

Exploring the ‘Wild West’ of sleep

Generally, in REM sleep, levels of the neurotransmitters that typically promote wakefulness like norepinephrine and serotonin decrease. Vijayan and the team linked lowered levels with the brain’s ability to inhibit fear expression cells, through rhythms sent between the front of the brain and the amygdala — a region connected to emotional expression. In PTSD patients, these levels remain elevated. As such, study authors explored how the levels observed in sleeping PTSD patients could affect these fear-linked rhythms.

The research models show that in the brain of PTSD patients, these elevated levels allow fear memories to roam free, unlike what happens in healthy people. They discovered that these patients may need higher frequency rhythms to get rid of these memories, which could potentially be a viable therapeutic target according to this team. The problem is that much of sleep neuroscience research has been conducted on non-REM sleep, which describes the phases of moving from light to deep sleep. With that in mind, Vijayan refers to REM sleep as the “Wild West” in terms of what’s known about it in relation to memory.

“REM sleep is a lot harder to get your hands around,” says Vijayan, an assistant professor in the School of Neuroscience, part of the Virginia Tech College of Science, in a university release. “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.”

Scientists may have found a way to end these nightmares

During these experiments, the team reduced the norepinephrine and serotonin levels to represent typical REM sleep in order to normalize the rhythms. In doing so, they found that fear memories were successfully inhibited. More specifically, they found that a certain frequency of brain rhythms was especially effective at repressing fear expression cells. Lower-frequency theta rhythms of around four hertz, which is the main unit of frequency, were most effective at strengthening connections between the parts of the brain needed to keep fear memories at bay.

Theta rhythms help coordinate brain activity between the regions of the brain that are involved in learning and memory. In humans, they are typically around four to eight hertz. Researchers then modeled REM sleep in people with PTSD, mimicking the conditions as the first experiment. To their surprise, they didn’t notice the same trends.

“I’m a little surprised that the four hertz didn’t work,” Vijayan adds. “I thought maybe it would still be effective, but it really wasn’t at all.”

By narrowing down the focus to these rhythms, scientists may have found a beneficial path to helping PTSD patients sleep more soundly. The main premise could even be applied to other brain conditions as well.

“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,” Vijayan concludes.

The findings are published in the journal JNeurosci.