Human volunteers who learned that a certain visual signal leads to an electric shock were more likely to respond fearfully to the signal days later when they were sleep-deprived, compared with controls allowed to sleep normally, a researcher said here.
The finding suggests that “treating sleep [problems] might enhance treatment of PTSD” or post-traumatic stress disorder, said Laura Straus, a doctoral candidate at the University of California San Diego who led the prospective, parallel group study.
Straus presented the study in a platform session atSLEEP 2015, sponsored by the Associated Professional Sleep Societies.
After being trained to associate a blue circle with electric shock (a low-level current applied to the wrist), those who were then made to stay awake 36 consecutive hours the next day were more likely to still be showing electromyographic patterns in the eyelid (blink EMG) that are known to signal fear, she said.
A number of animal experiments involving extreme sleep deprivation had previously indicated that fear responses were prolonged when rodents were kept awake. In particular, both the extinction of fear (which normally occurs within a day or two) and the subsequent retention of that extinction were impaired in sleep-deprived animals. But such an experiment with human subjects has not been reported before, Straus said.
For the trial, she and colleagues recruited 61 mostly young, healthy volunteers (mean age 24, range 18-38) of whom 39% were women. They were randomized to three groups and, over the course of 4 days, tested four times with blink EMG: once at baseline, once after the shock training, and twice more over the later days.
For the shock training, all participants underwent a series of short sessions during which they were shown either a blue or a yellow circle. When it was blue, a shock was delivered; when yellow, no shock was delivered. At the end of this and subsequent sessions, participants underwent blink EMG testing when shown the colored circles.
At the next session, the next day, participants were again shown the blue and yellow circles in repeated sessions, but this time no shocks were delivered with either one. Ordinarily, blink EMG-signaled fear responses to the blue circle would be attenuated in this session as part of the fear extinction process.
The final session was structured similarly. Again, the normal response is an attenuation of responses to the blue circle.
The group assignments varied the timing of sleep deprivation. In the control group, they were allowed to sleep normally throughout the study. Group 2 was made to stay awake 36 hours between the training session and the next session that would measure fear extinction. In the third group, the 36-hour sleep deprivation occurred between the third and final testing sessions, so possibly affecting recall of extinction but not affecting the initial strength of the extinction.
Results were that, compared with the controls, Group 3 showed no significant differences in the attenuation of fear responses over the course of the study.
This impairment of extinction recall is similar in many ways with the development of PTSD in humans, and the role of sleep deprivation is especially relevant in the context of military personnel. In battle (and often elsewhere in the general theater of combat operations) people often go without sleep for more than 24 hours.
Some previous studies in humans have suggested not only that trauma leads to sleeplessness, and also that sleep deprivation prolongs retention of fearful memories and associations, but not with a prospective design and such long periods of deprivation, Straus said.