Everyone has emotionally charged dreams from time to time. But people with post-traumatic stress disorder often have the same distressing, even terrifying dream night after night. It’s as if the brain is unable to dissipate the emotional charge, condemning the sufferer to a torturous feedback loop.
Why?
Sujith Vijayan has an explanation. And though it’s early in the research, he’s also got ideas on how to break the cycle.
Vijayan is an associate professor in Virginia Tech’s School of Neuroscience who specializes in sleep. Earlier this year the Journal of Neuroscience published the results of his computer modeling study (with two co-authors) of sleep in PTSD patients.
In the first part of a sleep cycle, we usually experience deep, restorative sleep. Later in the sleep cycle we experience rapid eye movement (REM) sleep with its vivid dreams. REM is important for processing emotional memories. If something goes wrong in REM, the sufferer may be unable to dissolve the fear reaction that’s associated with a memory.
In normal sleep, the level of norepinephrine, a neurotransmitter, drops during REM. “But in PTSD patients, the norepinephrine remains high,” Vijayan said in an interview in his office at Tech’s Institute for Critical Technology and Applied Science (ICTAS). “In the model, we looked to see what happens. And we found that, in fact, the normal brain rhythms that are useful for dissipating the emotions to the memory aren’t effective in PTSD,” due to the altered neurotransmitter levels.
These rhythms are the electrical brain waves that everyone has. They vary in frequency with the different stages of sleep. Manipulating brain rhythms by presenting soft auditory stimulation while asleep could lead to therapies that restore the healing quality of sleep in PTSD patients, Vijayan believes.
The interventions suggested by Vijayan “might actually have really dramatic therapeutic impacts,” said Sarah Clinton, interim director of the School of Neuroscience. “To me, that’s part of what is super exciting about what he’s doing.”
Like a physicist who’s equally adept in the lab and at the blackboard, Vijayan does lab-based studies in addition to the computer modeling work.
Down the hall from his office on the second floor of the ICTAS II building is a nondescript sleep lab, with barely enough room for a computer desk, sleep recording equipment, and a twin bed. Acoustic foam tiles on the wall dampen sound.
Here, when most Tech students are snoozing in their dorms or apartments, Vijayan’s assistants record sleep data from student volunteers.
The team experiments on psychology undergrads. The volunteers typically receive extra credit for classes, although sometimes they are paid.
Vijayan does two different types of studies, nap studies and overnight. The nap studies are about 90 minutes long. Overnight subjects are asked to show up around an hour before their normal bedtime.
The assistants attach an EEG (electroencephalogram) cap bristling with electrodes to record brain waves. EOG (electrooculogram) electrodes below the eye record the eye movements of REM. EMG (electromyogram) electrodes on the chin record muscle tension. Paralysis is a hallmark of REM. The equipment helps distinguish between REM and non-REM sleep.
Vijayan is interested in the connection between sleep and learning. Before sleeping, the subject is trained on a computer memory game. A series of pictures appears on a checkerboard-like grid. Each picture has a specific location. To aid in memorization, the subject hears a sound associated with each picture. When a piano keyboard appears, a piano sound is heard. A cow picture is paired with a moo, a cat with a meow, a clock with a ticking sound. After training comes the test: the subject must drag each picture to its correct grid location.
Some subjects have trouble nodding off with electrodes stuck to the head and face, but the vast majority are able to sleep. After they doze off, often during non-REM sleep toward the beginning of the sleep cycle, the grad students or research technicians play, over speakers, some, but not all, of the sounds the subject heard during training. “We try to play it so it’s not perceptible,” Vijayan said. “So most of the studies, when people ask them, ‘Did you hear any sounds?’ They say no.”
In the morning, the subject is retested on the memory game. Subjects remember more accurately the locations of pictures for which they heard the paired sound during sleep, versus the control pictures for which no sound was presented.
“During sleep, we’re probably processing all sorts of memories and strengthening them. But probably what happens is when we play a specific sound associated with a specific memory, it’s probably giving that memory some sort of priority or preference.”
This effect is well documented. Vijayan is trying to identify the exact mechanism.
At Carilion Roanoke Memorial Hospital, Vijayan gathers data that he can’t get in the Tech sleep lab. Patients with drug-resistant epilepsy are in the hospital while doctors assess them for possible surgical treatment.
Sleep testing is not the main reason they’re there, but when they consent, Vijayan and his team perform the same types of memory tasks they do in Blacksburg, with an important difference: they are able to obtain information from electrodes that have been surgically implanted in the brain. Compared to scalp electrodes, the implanted electrodes provide a much higher resolution picture of brain activity.
Most implanted electrodes are placed using a highly accurate robotic tool, according to Dr. Mark Witcher, a Carilion neurosurgeon and member of the Virginia Tech Carilion School of Medicine faculty. “VTC was an early adopter of this technology and originally introduced its use to Virginia,” he said. Witcher typically places 14 to 16 electrodes, each with up to 24 contacts. The electrodes helps doctors localize the origin of the seizures.
“Many of the same structures monitored for seizure onset play vital roles in normal cognitive processes such as memory acquisition and consolidation, emotional processing and other types of cognitive processing,” Witcher said.
“We can look at how those structures are interacting with the rest of the brain in consolidating memories,” Vijayan said. “Nationally and internationally that has led to a lot of insights into what’s going on in the brain in humans.”
“Dr. Vijayan is a world leader in understanding the relationship between sleep rhythms and memory,” said Michael Fox, dean of the College of Natural Sciences at the University of Massachusetts, Amherst, and former director of Tech’s School of Neuroscience.
As to whether students might someday prepare for a music recital, calculus exam or chemistry final using sleep learning, “It’s a very interesting question,” Vijayan said. “It’s a kind of question of my students would be very interested in, but I don’t think we know.”
Vijayan and other researchers have uncovered many of the mysteries of sleep. But there is much that remains in the dark.