Improve your memory by nodding off

Research has revealed how the replaying of memories while we are awake leaves them vulnerable to interference and distortion. The study, published in the journal Nature Neuroscience, showed that by reactivating these memories during our sleep, they are protected from this manipulation, particularly during slow wave sleep (SWS). SWS occurs in stages 3 and 4 of non-REM sleep, and we will normally SWS in periods of longer than 20 minutes, or extended power naps.

In this study, volunteers were required to remember the locations of pairs of cards, officially referred to as a concentration-type game. Whilst playing, the volunteers were exposed to an unspecified unpleasant smell. After this admittedly tiring game, half of the volunteers spent 40 minutes awake whilst the others curled up and took a 40-minute nap. Some volunteers, both awake and asleep, were again exposed to the smell in an attempt to reactivate their memory of the card game. After the 40 minutes were up all of the volunteers played the game one more time and then their ability to recall the original pairs of cards from the first game was tested.

Those volunteers who hadn’t had their memory jogged by the odour, whether awake or asleep, were able to remember around 60% of the original card pairs. An interesting result came from those volunteers whose memories had been reactivated with the smell. Those who had foregone the nap and stayed awake for 40 minutes were only able to remember around 41% of the card pairs. Their memories, having been reactivated whilst they were awake, were vulnerable to interference probably from the second game of ‘pairs’. Those volunteers whose memories had been jogged during their sleep successfully recalled the location of 84% of the original pairs. Brain scans taken during the research revealed how memory replay during SWS involves much stronger activity in the hippocampus (a structure in the brain strongly associated with memory formation) where short term memories are transferred to be stored as long term memories in the cortex. Replaying memories during these periods may speed up the transfer from long to short-term memory, stabilising it.

The research scientists, from various German and Swiss universities, believe their findings may have important clinical implications, namely those of improving psychotherapy techniques. It is suggested that these results mean that contextual cues presented during wakefulness may be able to reactivate unwanted or maladaptive memories during psychotherapy, in patients with post-traumatic stress or panic disorder. Being able to reactivate these unwanted memories before therapy may allow traumatic memories to be ‘unlearnt’ and replaced with ‘new’ memories. Reactivation of these new memories during periods of SWS could then stabilise these new therapeutic memories within the brain of the patient.