Many of us might remember our parents insisting that we get a good night’s sleep before a big exam or test, with the argument that being well rested would help us perform at our best. Although we may not have believed our parents back then, perhaps we should have. Research is showing that sleep plays an important role in the stabilization and strengthening of memories. In particular, research has shown that sleep makes memories more resistant to interference from competing lexical information.
The authors of a recent article in the journal Cortex wondered if sleep could also protect memories from emotional interference. To find out, they induced participants to feel happy or sad by having them listen to an emotionally charged classical piece of music. As they listened to the music, participants imagined themselves emotionally engaging in several sad or joyful situations, such as the death of a fond pet. Participants then studied a list of unrelated word pairs (e.g., Horse – Lounge). Half the participants were then allowed to sleep as they normally would, while the other half were deprived of sleep. Two days later, they returned to the lab where the researchers induced the same or the opposite emotion and tested them for a second time on the word pairs.
According to the network theory of affect, memory for information should be better when the emotion induced at the time of recall matches the emotion induced at the time of encoding (the first stage of memory processing). Because the emotion and the piece of information become linked in memory, the emotion serves as a cue for the to-be-remembered information and facilitates recall. In contrast, inducing an emotion during recall that is different from the emotion felt at the time of encoding can interfere with recollection of the target information.
The researchers found that word pairs were recalled more accurately when the emotion induced during recall matched the emotion induced during encoding — but only for the sleep deprived group. Why might this be? The researchers hypothesize that sleep decouples target information from the emotion felt at the time of encoding, meaning that the memories are less sensitive to the facilitation or interference provided by the particular emotional state induced at recall.
This finding adds to research highlighting the way that sleep affects the consolidation of our memories, but there is still much more to learn. Future studies should examine whether sleep similarly affects other types of context-linked memories — information linked to a smell or place, for example — and whether the emotional decoupling observed in this experiment occurs during a specific point in the sleep cycle.
Deliens, G., Gilson, M., Schmitz, R., & Peigneux, P. (2013). Sleep unbinds memories from their emotional context Cortex, 49 (8), 2221-2228 DOI: 10.1016/j.cortex.2012.11.014