Late sleep (rich in REM sleep) may enhance fear extinction recall in likely PTSD, and sleep restriction may have an unexpected protective effect, though this may reflect sleep rebound during recovery.
Key Findings
Results
A significant three-way interaction was found between time, sleep group, and PTSD status for skin conductance response (SCR).
The interaction of time (late extinction, early recall) x sleep group (early, late, normal) x PTSD status was statistically significant (p = .009, ηp2 = 0.30)
Linear mixed-effect models were used to analyze the data
SCR was used as the primary physiological measure, indexed via skin conductance response
70 adults participated (M age 25.78 ± 6.71 years; 32.86% with likely PTSD)
Results
In individuals with likely PTSD, SCRs to the threat signal decreased following late sleep compared to normal sleep.
Late sleep is characterized as the second half of the night, which is rich in rapid eye movement (REM) sleep
The decrease in SCR to the threat signal was observed specifically in the likely PTSD group, not in those without PTSD
This effect was measured at the late extinction time point
Sleep was monitored via actigraphy rather than polysomnography
Results
Both sleep restriction groups with likely PTSD showed lower SCR towards the threat signal at recall compared to normal sleep.
Both early sleep restriction and late sleep restriction groups with likely PTSD demonstrated this effect at recall testing
The authors note this may reflect an 'unexpected protective effect' of sleep restriction in likely PTSD
A recovery night of sleep was provided before recall testing, and the authors suggest the effect 'may reflect rebound of sleep during the recovery night'
Recall testing occurred after a recovery night of normal sleep
Results
No significant recall effects were found for threat expectancy ratings in any group or sleep condition.
Threat expectancy ratings were used as a secondary subjective measure alongside physiological SCR
The absence of effects in threat expectancy ratings contrasts with the SCR findings
This suggests that the sleep-related effects on extinction recall in PTSD may be specific to physiological rather than subjective threat responses
Methods
The study used a two-day fear conditioning paradigm with sleep manipulation between extinction learning and recall testing.
Participants completed extinction learning on day one, then were assigned to one of three sleep conditions: early sleep restriction (first half of night), late sleep restriction (second half of night), or normal sleep
After a recovery night, participants returned for extinction recall and safety recall testing
70 adults were enrolled, with 32.86% meeting criteria for likely PTSD
Sleep was monitored via actigraphy throughout the study
The authors note that polysomnography was not used and that 'further research using polysomnography is required to confirm these results'
Background
The study examined both extinction memory (previously threatening stimuli are now safe) and safety memory (stimuli signalling absence of threat) consolidation in relation to sleep timing.
Sleep disturbances are described as 'a key feature of posttraumatic stress disorder (PTSD)' and are implicated in extinction and safety memory consolidation
The paradigm assessed both extinction and safety recall as separate memory processes
Both skin conductance response and threat expectancy ratings were used to index these memory processes
Trauma-exposed adults with and without likely PTSD were compared
What This Means
This research suggests that the timing of sleep after learning that a feared situation is actually safe may matter differently for people with PTSD compared to those without it. In this study, 70 adults who had experienced trauma—about one-third of whom met criteria for likely PTSD—went through a fear learning and 'unlearning' (extinction) experiment over two days. After being taught that a previously scary signal was no longer dangerous, participants were assigned to sleep only in the first half of the night, only in the second half, or a full night, before returning the next day to test how well they remembered that the signal was safe.
The key finding was that people with likely PTSD who slept in the later half of the night—which contains more REM (dreaming) sleep—showed lower physiological fear responses (measured by sweat on the skin) to the threat signal compared to those who had a normal night's sleep. Interestingly, both groups with restricted sleep and likely PTSD also showed reduced fear responses at the recall test the following day, though the researchers caution this could be due to a 'rebound' of sleep during a recovery night provided before testing. These effects were only seen in the body's automatic stress response and not in participants' conscious ratings of how threatening they expected the signal to be.
This research suggests that REM-rich late-night sleep may play a helpful role in strengthening fear extinction memories in people with PTSD—potentially relevant for understanding why sleep problems in PTSD can interfere with recovery, and why therapies like exposure-based treatments might be affected by sleep patterns. However, the authors emphasize that the study used wrist-worn actigraphy rather than full sleep monitoring, and that more precise sleep measurement studies are needed before firm conclusions can be drawn.
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