Encoding or consolidation? The effects of pre- and post-learning propranolol on the impact of an emotional scene

Abstract

Background and objectivesResearchers have conceived of post-traumatic stress disorder (PTSD) as a disorder of memory, and proposed that blocking the impact of stress-related noradrenaline release in the aftermath of trauma may be a way of preventing the ‘over-consolidation’ of trauma-related memories. Experimental research in humans has been limited by typically focusing on declarative memory for emotional stories, and has mainly given propranolol before learning. In contrast, the clinical studies that we comprehensively review are hampered by practical challenges, such as reliably administering propranolol in a time window sufficiently close to the traumatic event. In this study, we aimed to assess the impact of both pre- and post-learning propranolol on emotional and declarative memory for an emotional scene, using the ‘trauma film paradigm’. MethodsTo control for drug and timing effects, participants received a pill (40 mg propranolol or placebo) both 60 min before and within 5 min after viewing a 12 min, emotionally arousing trauma film, and were assigned to one of the three conditions: propranolol-placebo (n = 25), placebo-propranolol (n = 25), or placebo-placebo (n = 25). We assessed participants’ immediate emotional responses to the scene, as well as delayed impact (intrusions, Impact of Events Scale) and declarative memory. ResultsUsing Bayesian informative hypothesis testing, we found that pre-learning propranolol reduced the initial emotional impact of the ‘trauma film’. However, we did not find strong evidence for an impact of pre- or post-learning propranolol on later consequences of having watched the emotional film (intrusions, Impact of Events, or tests of declarative memory). Exploratorily restricting analyses to women, we did find evidence suggesting that pre-encoding propranolol could reduce the rate of intrusions and self-reported negative impact of the emotional scene one week later. LimitationsFloor effects in the delayed impact of the emotional scene could preclude observing differences as a function of propranolol, and propranolol dosage may need to be increased. ConclusionsAn impact of propranolol on encoding could raise difficulties in interpretation when only pre-encoding propranolol is used to make inferences about consolidation. We discuss the challenges of elucidating the mechanistic underpinnings of propranolol's reported effects on memory.