Late sleep enhances fear extinction recall in posttraumatic stress disorder.

Sleep disturbances are a key feature of posttraumatic stress disorder (PTSD) and is implicated in extinction (i.e., previously threatening stimuli are now safe) and safety (i.e., stimuli signalling absence of threat) memory consolidation. This study examined whether early sleep versus late sleep impacts extinction and safety recall, indexed by skin conductance response (SCR) and threat expectancy ratings, in trauma-exposed adults with and without likely PTSD. Seventy adults (M age 25.78 ± 6.71 years; 32.86% with likely PTSD) completed a two-day fear conditioning paradigm. Following extinction learning, participants were assigned to sleep restricted to the first half of the night, the second half, or normal sleep, monitored via actigraphy. After a recovery night, participants returned for extinction and safety recall testing. Linear mixed-effect models revealed a significant time (late extinction, early recall) x sleep group (early, late, normal) x PTSD status (likely no PTSD, likely PTSD) interaction (p = .009, ηp2 = 0.30). In likely PTSD, SCRs to the threat signal decreased following late sleep compared to normal sleep. At recall, both sleep restriction groups with likely PTSD had lower SCR towards the threat signal than normal sleep. No recall effects were found for threat expectancy ratings. These findings suggest that late sleep (which is rich in rapid eye movement sleep) may enhance extinction recall, and sleep restriction may have an unexpected protective effect in likely PTSD. However, the latter effect may reflect rebound of sleep during the recovery night. Further research using polysomnography is required to confirm these results.