Effects of THC intoxication on false memories in a legal context

Rationale: False memories refer to memories of events/details that did not occur. False memories frequently occur spontaneously but can also be elicited through suggestion. Legal cases have shown that eyewitnesses and innocent suspects can falsely remember to have seen non-existing details of a crime or falsely confess to have committed a crime due to suggestive interrogation tactics of the police. Such false memories can lead to wrongful convictions. Eyewitnesses and suspects are often under the influence of cannabis but little knowledge exists whether their drugged state makes them more vulnerable to spontaneous or suggestion-induced false memories. From a practical perspective, examining this issue is highly relevant as cannabis is the most widely used drug in the world. Demonstrations of drug-induced false memories may be extremely relevant in the courtroom and in forensic examinations.



Objective: The current project will examine the impact of cannabis intoxication on susceptibility to false memories and dissociation and assess whether such drug-induced experiences depend on an underlying dissociative state or trait. Individual factors of potential influence on false memory (such as attention, compliance) and subjective experience will also be assessed.



Study design: Acute and delayed influences of cannabis on false memory formation will be assessed in a double-blind, placebo-controlled study in occasional cannabis users, using a virtual reality (VR) eyewitness and a perpetrator scenario. The order of treatments and scenarios will be counterbalanced across participants.



Study population: Sixty-four healthy, occasional cannabis users, aged 18-40.



Intervention: Placebo and cannabis vapor (300 μg THC/kg bodyweight)



Main study parameters/endpoints: Spontaneous and suggestion-based false memories will be assessed by using established false memory paradigms (associatively-related word lists, misinformation paradigm). Dissociative states and traits will be assessed using both established self-report and clinician-administered measures.



Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Participants will inhale placebo and cannabis vapor and be exposed to two distinct mock crime scenarios on two separate occasions, each followed by an immediate and a one-week follow-up assessment, including measures of true and false memory and dissociative states and traits.

Cannabis intoxication will increase sensitivity to suggested and spontaneous false memories during interrogations

immediate (after administration of cannabis/placebo) and delayed (one week after administration)

300μg THC/kg bodyweight