Can the double orexin receptor antagonist suvorexant increase rapid eye movement (REM) sleep and improve sleep-dependent processing of emotional memories in healthy adults?

INTERVENTION: This Randomized Controlled Trial (RCT) investigates whether the double orexin receptor antagonist suvorexant increases rapid eye movement (REM) sleep and improves fear extinction recall compared to an active control condition (temazepam) and placebo control. Participant will be recruited and randomly assigned to the double‐blinded drug condition. The intervention group receives one dose of 20mg suvorexant orally about 30 minutes before bedtime. On the test day, participants will complete a standardized and well‐validated fear conditioning and extinction task which examines their capacity to acquire conditioned fear (via recording skin conductance response [SCR] reflecting physiological arousal to stimuli paired with a mild electric shock) and extinguishing fear. For the fear acquisition phase, they will look at visual images of a scene containing a desktop lamp which lights up with a color. One color will be associated with a mild electrical shock (the CS+), the other colored circle is never associated with shock (the CS‐). This will be followed immediately by the fear extinction phase in which they will look at both colored lights which will never be followed by shock. This paradigm is adapted from Milad, Orr, Pitman, & Rauch (2005). SCR will be recorded to reflect sympathetic arousal. SCR amplitude typically increases to the CS+ compared to the CS‐ in the acquisition phase, and then gradually reduces over the extinction phase. The slope of decline of SCR over the fear extinction phase reflects how well an individual can inhibit/regulate their fear and reflects their capacity for fear extinction learning. Next, participants view emotive and neutral images selected from the International Affective Picture System (IAPS). Then, participants will take the drug and sleep at the lab while polysomnography (PSG) records sleep including REM sleep during the test night. This is followed by a recovery night at home to allow full drug washout (an ambulatory PSG recor CONDITION: Mental Health ‐ Other mental health disorders PTSD; ; PTSD PRIMARY OUTCOME: Amount of REM sleep visually scored from the PSG output.[1. Test night (night after drug intake); 2. Home sleep recording (2nd night after drug intake); ] Fear extinction recall measured via SCR[Follow up (about 48h after drug intake).] SECONDARY OUTCOME: Group differences on fear conditioning measured via SCR.[Test day] Group differences on fear extinction learning measured via SCR.[Test day] Number and description of intrusive memories (assessed from the open‐ended question of the intrusive memory diary).[Every day during the week after the follow up.] Rating of distress of intrusive memories (0=not at all, 10=extremely).[Every day during the week after the follow up.] Rating of vividness of intrusive memories (0=not at all, 10=extremely).[Every day during the week after the follow up] INCLUSION CRITERIA: 1. Aged between 18 – 50 years’ old 2. Physically and mentally healthy 3. Proficient in English