A new study says that the best way to remember something important is to remember it while you are asleep. The research, led by Bjorn Rasch of the University of Basel in Switzerland says that newly learned memories during sleep rather than when awake does a better job of strengthening the memory trace. This could help people with disorders such as post-traumatic stress disorder (PTSD) feel researchers.
For the study the team trained subjects in a spatial memory task to learn an object’s location in a grid. At the same time an odour was released. This was done so as to associate the memory with the smell. One group then went to sleep, while the second group stayed awake. After 20 minutes while the sleeping group’s brain wave patterns were in slow wave sleep (SWS), both groups were subjected to the same odour again to reactivate the memory. After another 20 minutes, the participants in the sleeping group were woken, and both groups were given a similar task, but the objects were in different locations and without the odour. 30 minutes later they were asked to recall the position of the cards from the original task.
Results showed that both groups were correct about 60 per cent of the time without any odour assistance. But once the odour was added to the test, the non-sleeping group were only correct about 42 per cent of the time, compared to the sleeping group’s 84 per cent.
The researchers said, “As we expected, reactivation during waking destabilized memories. In contrast, reactivation during SWS immediately stabilized memories, thereby directly increasing their resistance to interference.” Susanne Diekelmann, one of the lead researchers said, “Reactivation of memories had completely different effects on the state of wakefulness and sleep. Based on brain imaging data, we suggest the reason for this unexpected result is that already during the first few minutes of sleep, the transfer from hippocampus to neocortex has been initiated.”
Diekelmann added that after only 40 minutes of sleep, significant chunks of memory were already “downloaded” and stored where they “could no longer be disrupted by new information that is encoded in the hippocampus”. This could have implications for memory-intensive activities such as language training she said. The findings, she said, also point to a strategy for helping victims of post-traumatic stress syndrome, a debilitating condition caused by extreme experiences. The reactivation techniques “might prove useful in re-processing and un-learning unwanted memories,” she said. “And reactivation of newly learned memories during ensuing sleep could then help consolidate the desired therapeutic effects for the long-term.”
The study appears in this week’s Nature Neuroscience.
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