The complexities of memory suppression
5/22/12

Memories have their virtues, but so does forgetting. If our episodic and potentially unlimited memory did not get rid of the many memories that have no bearing on our objectives, pursuing the latter would be hampered by this mass facing our cognitive resources. A team from the University of Liège took a closer look at the cerebral mechanisms of intentional forgetting. This original work was recently the subject of an article in the journal Plos One.

Cerveau-sommeilOur memory isn’t a monolithic entity, but a set of interacting independent systems and sub-systems, each with it specific cerebral bases.  Remembering two numbers for a brief moment for the purpose of mental arithmetic doesn’t rely on the same processes as those that allow us to remember that Buenos Aires is the capital of Argentina, or those that underpin the storage and retrieval of personal experiences, such as having eaten in a new Italian restaurant with two work colleagues last week. If we refer to the model proposed in 1995 by Endel Tulving from the University of Toronto, the memory system that comes into play in the first case is the working memory; second is semantic memory and third, episodic memory.

Tulving, whose work remains the reference, suggested the existence of five main memory systems: four relating to long-term memory (episodic, semantic and procedural memories as well as the perceptive representational systems) and one focused on the short term, i.e., the working memory. The latter, whose mission is to temporarily maintain a small quantity of information in an easily accessible form while various cognitive tasks are being processed – mental arithmetic, dialling a phone number we have just found in the directory, etc. – has limited resources since, as we all know from experience, we are incapable of simultaneously remembering numerous pieces of information intended for immediate processing.

“On the other hand, episodic memory is potentially unlimited in the sense that any event experienced by an individual is encoded and processed by the brain and can theoretically be memorised”, explains Christine Bastin, post-doctoral neuropsychologist and researcher at the Cyclotron Research Centre (CRC) at the University of Liège. Nevertheless, she adds that the majority of things we experience do not relate to our basic goals, have no deep meaning for us and will consequently be spontaneously eliminated from our memory.

Positivity bias

If the episodic memory didn’t eliminate anything, and if it kept the trace of elements irrelevant to our goals, our cognitive resources would be unnecessarily overloaded. Fabienne Collette, senior research fellow for the FNRS at CRC and ULg’s neuropsychology unit, considers that even our social relations would be disrupted if we didn’t forget numerous pieces of ultimately irrelevant information, resulting from our experiences. “If, for instance, remembering the least incident between you and another person was likely to invade your mind every minute of the day, it would be difficult for you to maintain a harmonious relationship with this person", she says.

A few cases of hypermnesia have been recorded. Those concerned are unable to forget. At the slighted opportunity, the memory of negative events, even minor, resurface, making the life of the sufferer unbearable; they complain that they are overcome by this memory. “Forgetting is adaptive”, Fabienne Collette insists.

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