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Some new research has shown that cannabis consumption, or to be more exact intoxication with tetrahydrocannabinol (THC), which is a compound in cannabis, increases susceptibility to false memory. These findings have significant legal implications.

A group of researchers, composed of Lilian Kloft, Ph.D. from the Faculty of Psychology and Neuroscience at Maastricht University, in the Netherlands and her colleagues begun to investigate the effects of cannabis consumption on memory formation.

Cannabis affects memory and earlier studies note that “acute and chronic exposure to cannabis” affects verbal memory, learning, and attention.

The consequences of cannabis consumption on memory is an important issue that has gained a lot of interest in the last few years, including from a legal perspective, according to the researchers.

Convictions usually rely on the testimonies and memories of eyewitnesses, but sometimes memories can be false. Memory “malleability” refers to the fact that our brain is able to create false memories based on events that didn’t even happen, based on our past experiences, or even plant completely false memories into someone else’s mind.

You probably wonder, how does cannabis consumption can affect one’s susceptibility to false memories? To find out, Kloft and her team of researchers tested the effects of tetrahydrocannabinol intoxication upon the memories of 64 healthy participants to the study.

They published their results and findings in the journal Proceedings of the National Academy of Sciences.


Studying cannabis use and false memories

The researchers approached a double-blind, placebo-controlled and randomized research, in which they wanted to find the effects of THC intoxication on the possibility of creating false memories. They compared the results with those of a placebo group instead of the drug.

The researchers examined the participant’s memories straight after the THC intoxication or the use of the placebo, and again one week after, using associative word lists and two misleading tasks.

The first task made the participants look at 15 lists of related words. The THC group was more likely to say recognized words that they hadn’t been shown to them previously, compared to the placebo group.

The second task was made by using virtual reality to achieve the same exact experience as of a fight at a train station and the theft of a handbag in a bar.

The first scenario had the participants being eyewitnesses, while in the second one, they were the perpetrators. After seeing the scenario, the researchers asked the participants some questions about what had happened there.

During these interviews, the researchers gave them inaccurate information by introducing the testimony of a second eyewitness or by asking misleading questions on purpose.


THC intoxication raises false reporting risk

This study’s results have revealed that the first group with the THC intoxication was more likely to create false memories than the placebo group. Moreover, when they repeated the same exact experiment one week later when the group was sober, they still had the same exact susceptibility to forming false memories.

“Cannabis seems to increase false memory proneness, with decreasing strength of association between an event and a test item, as assessed by different false memory paradigms,” conclude the researchers.

“Our findings have implications for how and when the police should interview suspects and eyewitnesses,” they add.

“In terms of interviewing witnesses, victims, or suspects after the incidence of a crime, this means that interviewing while the individual is still intoxicated should be minimized, due to elevated risk of false reporting,” explain Kloft and colleagues.

“Our findings show that it would be better for police officers and investigators to postpone the questioning of eyewitnesses and suspects who are under the influence of cannabis until they are sober,” comments Prof. Johannes Ramaekers, the final author of the study.

“People under the influence of cannabis should actually be treated as a vulnerable group in a criminal investigation, comparable with children and the elderly.” – Prof. Johannes Ramaekers

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