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Forget suppressed memories

A recent paper (see citation) has put a hole in another remnant of Freud’s influence, that suppressed memories are still active. Freud noticed that we can suppress unwelcome memories. He theorized that the suppressed memories continued to exist in the unconscious mind and could unconsciously affect behaviour. Uncovering these memories and their influence was a large part of psychoanalysis. Understanding whether this theory is valid is important for evaluating recovered memories of abuse and for dealing with post-traunatic stress disorder.



The question Gagnepain, Henson and Anderson set out to answer was whether successfully suppressed conscious memories were also suppressed unconsciously or whether they were still unconsciously active. They had subjects learn an association between a word and a picture for a number of pairs. After the pairs were well learned the word would bring the picture to mind. Some of the pairs were then deliberately suppressed through the subject attempting to not bring the picture to mind when the word was mentioned. This produced two sets of pictures in the subject’s mind: one set would come easily to mind (unsuppressed) and the other set was very difficult to bring to mind (consciously suppressed). But what would be the unconscious influence of the consciously suppressed pictures? The subjects were shown the pictures after they had been doctored to make them difficult to recognize. The ones that had been suppressed were not easier but harder to recognize then the unsuppressed ones. So the willful suppression weakened the memory consciously and also weakened the unconscious influence. This sequence was followed with scans which indicated that it was not just the retrieval of memories that was changed by the suppression but also the memories themselves. And further it was the visual-sensory aspect of the memories that was disrupted.



There are of course some flags to put up: the experiments were done on adults and might not apply to children; and, there was no high psychological stress involved that might change the storage or retrieval of highly emotional memories. However the results do fit with a number of other findings about memory, so that it is now unwise to take the Freudian view of suppression as reliable.



Here is the abstract:


After a trauma, people often suppress intrusive visual memories. We used functional MRI to understand how healthy participants suppress the visual content of memories to overcome intrusions, and whether suppressed content continues to exert unconscious influences. Effective connectivity, representational similarity, and computational analyses revealed a frontally mediated mechanism that suppresses intrusive visual memories by reducing activity in the visual cortex. This reduction disrupted neural and behavioral expressions of implicit memory during a later perception test. Thus, our findings indicate that motivated forgetting mechanisms, known to disrupt conscious retention, also reduce unconscious expressions of memory, pointing to a neurobiological model of this process.


Suppressing retrieval of unwanted memories reduces their later conscious recall. It is widely believed, however, that suppressed memories can continue to exert strong unconscious effects that may compromise mental health. Here we show that excluding memories from awareness not only modulates medial temporal lobe regions involved in explicit retention, but also neocortical areas underlying unconscious expressions of memory. Using repetition priming in visual perception as a model task, we found that excluding memories of visual objects from consciousness reduced their later indirect influence on perception, literally making the content of suppressed memories harder for participants to see. Critically, effective connectivity and pattern similarity analysis revealed that suppression mechanisms mediated by the right middle frontal gyrus reduced activity in neocortical areas involved in perceiving objects and targeted the neural populations most activated by reminders. The degree of inhibitory modulation of the visual cortex while people were suppressing visual memories predicted, in a later perception test, the disruption in the neural markers of sensory memory. These findings suggest a neurobiological model of how motivated forgetting affects the unconscious expression of memory that may be generalized to other types of memory content. More generally, they suggest that the century-old assumption that suppression leaves unconscious memories intact should be reconsidered.”


Gagnepain, P., Henson, R., & Anderson, M. (2014). Suppressing unwanted memories reduces their unconscious influence via targeted cortical inhibition Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1311468111

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