Memories beyond our wildest dreams

By Marie Rogers

During a long car journey to Edinburgh last Christmas, I managed to memorise the sequence of a whole pack of cards using mnemonic techniques. Mnemonics are just any method that helps you memorise information. For example, I used the ‘method of loci’ which involves linking items to certain locations. I was amazed at how effective these methods were.

One of the reasons it is so difficult to recall a series of items is that previous similar memories are easily confusable. This applies to our day-to-day, or ‘autobiographical’, memory too.  Actions we perform regularly are less easy to remember than unique events. Psychologists are unsure how the brain overcomes the problem of encoding similar memories in a way that we can recall them successfully. This is called the problem of ‘catastrophic interference’.

One theory about how memories are encoded is related to the function of dreams. During rapid eye movement (REM) sleep, we dream more frequently and our dreams tend to be more bizarre compared to non-REM sleep. In a review of the function of dreams, published this year, Sue Llewellyn proposes that REM dreams have ‘mnemonic properties’.

The techniques involved in mnemonics include the use of emotionally charged imagery (particularly fear, disgust, desire and elation), tagging information to particular locations, and the use of bizarre imagery. These features can also be seen in REM dreaming. Llewellyn’s idea is that dreams aid the encoding of new memories by associating them with old memories through bizarre links.

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Various neuroimaging evidence indicates the function of dreams may be related to memory. During REM dreaming, there is deactivation of the prefrontal regions of the brain, which are associated with logical, complex reasoning (Braun et al. 1997) along with increased limbic activity which is associated with emotion regulation. Furthermore, there is heightened activation of the area which deals with visual associations. These patterns of activation appear linked to the ‘hyperassociation’ that occurs during dreaming. That is, new and old memories are associated through bizarre links, which resemble the technique of mnemonics. This may indicate that the function of dreams is to encode our autobiographical memories in a way that allows effective retrieval.

It has often been assumed that the field of dreaming is unsuitable for scientific enquiry, due to its very personal and uncontrollable nature. But this theory presents various testable hypotheses about dreaming, and so opens up the area to study.

Artwork by Gina Parr