A preliminary investigation of the relationship between rapid eye movement (REM) sleep and fear inhibition processes in the context of circadian misalignment.
OBJECTIVE Rapid eye movement (REM) sleep is implicated in fear inhibition processes critical for trauma recovery. However, prior experimental models of REM sleep disruption have lacked ecological validity by manipulating sleep without accounting for circadian timing. Circadian misalignment frequently occurs in occupations at high risk of trauma exposure. The present study examined the relationship between REM sleep and fear inhibition in the context of experimentally induced circadian misalignment. METHOD A total of 42 healthy adults (Mage = 24.89, SD = 5.11) were randomized to one of three conditions for four nights: (a) normal control (n = 18), (b) circadian disruption with placebo administration (n = 14), or (c) circadian disruption with melatonin (3 mg) administration (n = 10). Circadian disruption consisted of two consecutive 4-hr phase advances. Fear inhibition was measured via the fear-potentiated startle task. Degree of circadian misalignment was measured via the phase angle between peak urinary 6-sulfatoxymelatonin and scheduled wake time. RESULTS Greater circadian misalignment on Night 4 significantly predicted larger reductions in both REM% (p = .010) and REM minutes (p = .002) that night. Controlling for changes in total sleep time and slow wave sleep, reductions in REM minutes on Night 4 significantly predicted poorer extinction recall the following day (ΔR² = .12, p = .040), whereas reductions in REM% showed a nonsignificant small-to-moderate association (p = .087). CONCLUSIONS Individuals experiencing greater reductions in REM sleep under circadian misalignment demonstrated poorer extinction recall. Interestingly, circadian misalignment predicted the same change in sleep (reduced REM minutes) also linked to poor extinction recall. Given the role of extinction recall in trauma-related psychopathology, these findings may have implications for frontline personnel at increased risk for posttraumatic stress disorder. However, larger samples are needed to confirm these preliminary findings. (PsycInfo Database Record (c) 2026 APA, all rights reserved).