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Riba J, Valle M, Sampedro F, Rodríguez-Pujadas A, Martínez-Horta S, Kulisevsky J, Rodríguez-Fornells A. 
“Telling true from false: cannabis users show increased susceptibility to false memories”. 
Mol Psychiatry. 2015 Mar 31.
Abstract
Previous studies on the neurocognitive impact of cannabis use have found working and declarative memory deficits that tend to normalize with abstinence. An unexplored aspect of cognitive function in chronic cannabis users is the ability to distinguish between veridical and illusory memories, a crucial aspect of reality monitoring that relies on adequate memory function and cognitive control. Using functional magnetic resonance imaging, we show that abstinent cannabis users have an increased susceptibility to false memories, failing to identify lure stimuli as events that never occurred. In addition to impaired performance, cannabis users display reduced activation in areas associated with memory processing within the lateral and medial temporal lobe (MTL), and in parietal and frontal brain regions involved in attention and performance monitoring. Furthermore, cannabis consumption was inversely correlated with MTL activity, suggesting that the drug is especially detrimental to the episodic aspects of memory. These findings indicate that cannabis users have an increased susceptibility to memory distortions even when abstinent and drug-free, suggesting a long-lasting compromise of memory and cognitive control mechanisms involved in reality monitoring.Molecular Psychiatry advance online publication, 31 March 2015; doi:10.1038/mp.2015.36.
Comments and Responses to this Article
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Status: display
earth
Apr 25, 2015 15:39
Unacceptable and Troubling Title and Findings : More Bad Science #

The authors and the journal should be ashamed for allowing the title and abstract of this article be published the way it is. This kind of hyped lying should be left to the crappy news sources. This is definitely a black mark against Molecular Psychiatry, the authors of this paper, and everyone involved.

The authors conducted a relatively simple game with abstinent cannabis users and a partially matched comparison group that had not used cannabis very much. The game-test was giving a long list of words (80 total), grouped by meaning, with a simple game to play while seeing them. Then, fifteen minutes later, they were shown words and asked whether each of the words shown had been in the original set. The second set was mixed half and half with words that were not part of the original set (80 new words) and asked to press a button yes or no indicating whether the word shown was part of the original set.

Half of the mixed in words were 'semantically related' and half were 'unrelated' words. The semantically -related words they called "lure" words.

Overall, there was little difference between abstinent cannabis users and 'controls', except on one measure. The authors write:

The analysis of behavioral data in the test phase showed no differences between groups in the number of correctly recognized studied words (true memory recognition; mean±s.d.: cannabis users, 64±6; controls, 65±6; t(30)=0.4, P>0.1) or in the number of correctly rejected new words (correct rejection of new words: cannabis users, 37±3; controls, 39±0.7; t(30)=1.9, P=0.076). No differences were found either in the time (in milliseconds) taken to correctly recognize studied words (cannabis users, 1185±199; controls, 1089±195; t(30)=−1.36, P>0.1), or to correctly reject new words (cannabis users, 1200±345; controls, 1043±196; t(30)=−1.58, P>0.1). However, as shown in Figure 1, cannabis users showed significantly more false memories.


The authors choose to characterize the pressing of the 'yes part of the original group' button for any of their 'lure' words as "false memories". The controls also had "false memories" almost as often as the abstinent cannabis users. On average, controls wrongly endorsed 8 lure words as having been part of the original set and cannabis users wrongly endorsed 12 lure words as original words.

Setting up a series of tests where only along one measure are scores statistically different brings into question any single finding, but worst of all is the extrapolation from clicking "yes" on "cow" when the original set of words included "horse", "hen", "sheep", and "goat" to the idea of "false memories".

Everyone involved in this should be ashamed for how this trivial game scoring was converted into "telling true from false"; "susceptibility to false memories"; "the ability to distinguish between veridical and illusory memories, a crucial aspect of reality monitoring that relies on adequate memory function [...] we show that abstinent cannabis users have an increased susceptibility to false memories, failing to identify lure stimuli as events that never occurred. ".

Sadly, it is more proof that what passes for "medical science" lives in a mirrored bubble where they reject the natural English meaning of words and sentences and continue to use the word "significant" indistinguishably to mean both "large and/or important" and "probably non-random using our math and of unknown importance".

Further, because this is a retrospective convenience population study, there is no way to determine that cannabis use was causal, even if we accept that their finding is interesting.

Perhaps the worst part about this garbage is that they then lay it on thick by using brain scans to prove that they can show the fMRI functional differences between the way these people with "false memories" differ from normals. It is definitely de jour, cool, and hip right now to take some weak negative finding and attempt to make it seem super sciencey by throwing some brain scans into the paper.

Take that fMRI away from them until they stop putting socio-cultural-political garbage into their article titles.

Shame on you.
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