Just One Hit of Weed May Lead to “False Memories”

New research finds that intoxication with tetrahydrocannabinol (THC), the psychoactive compound in cannabis, makes people more predisposed to forming false memories. The findings have significant legal implications. People who are high on cannabis are more likely to form false memories, in which they wrongly “remember” information that they never actually learned or recall snippets of an event that never happened.


Lilian Kloft, Ph.D. — of the Faculty of Psychology and Neuroscience at Maastricht University, in the Netherlands — and colleagues set out to investigate the effects of cannabis consumption on memory formation.

Cannabis is known to affect memory. Earlier studies have shown that “acute and chronic exposure to cannabis” impairs verbal memory, learning, and attention.

The impact of cannabis on memory, explain the researchers, is a particularly important issue that has attracted a lot of interest, including from a legal perspective.

Convictions often rely on the testimonies and memories of eyewitnesses, but memories are sometimes false.

“Malleability” of memory refers to the fact that are we able to create memories of events that did not take place, alter details of past experiences, and even plant completely false memories into someone else’s mind.

So, how does cannabis affect one’s susceptibility to such false memories? To find out, Kloft and the team tested the effects of THC intoxication on the memories of 64 healthy volunteers.

To test spontaneous false memories, the team turned to a well-known experiment known as the Deese-Roediger-McDermott (DRM) Task. In that experiment, volunteers memorize a list of related words — such as “tired,” “pillow,” “bed” and “snore” — and then get tested on their recognition of those words. The catch is that, during the testing round, learned words get mixed in with new words that the volunteers weren’t asked to memorize. In one experiment, the volunteers memorized a word list while high, and in another, they memorized a different list while sober.

The new words ranged from totally unrelated to highly related to the words on the original list. Typically, people wrongly remember highly related words despite not having seen them before.

They found the participants experienced both spontaneous false memories and those that the researchers actively suggested.

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In other words, if a witness was high during whatever event they’re being questioned about, they may believe — or become convinced — that things that never happened actually did.

As the team’s research paper, published Monday in the journal PNAS, reads, “the current study shows that intoxicated individuals might be at high risk to form all kinds of memory errors, which can be perilous in investigative interviewing settings.”

“The next step for us is to investigate the effects of cannabis in a ‘false confession’ paradigm,” lead researcher and Maastricht University psychopharmacology expert Lilian Kloft told Inverse. “False confessions are a major contributing cause to wrongful convictions and we cannot exclude that drug influence can magnify vulnerability for making a false confession.”

Why does this matter?

With state after state considering legalizing marijuana, a rise in false memories could play an increasingly larger role in criminal matters, said co-author Elizabeth Loftus, a professor of psychological science in the department of criminology at the University of California, Irvine.

“This new work is suggesting authorities need to be extra careful when interviewing somebody,” Loftus said. They should consider removing “them from a situation where they might be exposed to suggestive information that could contaminate their memory.”

And there’s the possible creation of false memories that affect friends, family and work colleagues.
“Formation of false memories may alter the interpretation of work-related activities and social interactions with others,” Ramaekers said.
“There are lots of situations where somebody’s memory matters,” Loftus said. “For example, a family dispute such as two siblings arguing about what happened in the past over a Thanksgiving table.”

In numerous studies over decades, Loftus has shown that when witnesses are given misinformation about something they saw, such as a mistake in the details, they will remember things that were only suggested to them after the event was completely over.

In the 1990s, she began to explore if it was possible to implant entirely false memories.”It’s one thing to make people think the perpetrator had a brown jacket instead of a green jacket, but could you plant entirely false ‘rich’ memories into the mind for something that didn’t happen?” Loftus asked

.”In one of the first studies done on this [subject], we made people remember that they were lost in a shopping mall as a child and had to be rescued and reunited with their family even though it never happened,” she said.Other researchers went so far as to implant memories of being “attacked by a vicious animal as a child; having a serious indoor or outdoor accident as a child; even witnessing somebody being demonically possessed,” Loftus said.

Could this happen to us all the time? Not likely, Loftus said.

“It’s very easy to distort memory for the details of an event,” she said. “It takes a lot more effort to plant one of these rich false memories.”

Do real memories come back?


In addition to witnessing the virtual train platform fight, subjects in the current experiment also underwent a first-person virtual reality scenario in which they became a student in need of money who steals a purse. In a third experiment, they were asked to recall words they had never been given.

“This study showed that cannabis increased the number of false memories across all three memory paradigms,” Ramaekers said.

While science isn’t completely sure why, researchers suspect that cannabis activates receptors in the hippocampus, the memory center of the brain, possibly producing “fragmentation of thought, loosening of associations and heightened distractibility,” he said.

However, when asked to recall the words or events a week later, the study found no real difference between cannabis users and the control group. They were able to recall the events as they actually occurred.

“The findings suggest that investigative interviewers should minimize the questioning of cannabis-intoxicated eyewitnesses and suspects, and instead wait until the first possible time after sobriety is reached,” Ramaekers said.
The same advice might apply to family and friends, especially for habitual users of weed.

There is evidence “that chronic use of cannabis can produce persisting decline of cognitive [or] memory function, even after prolonged abstinence and no THC in blood,” Ramaekers said.

source: https://www.pnas.org/content/early/2020/02/04/1920162117

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