Conference News Roundup—Society for Neuroscience

The Brain Preferentially Reactivates Negative Memories During Sleep

The brain selectively reactivates negative memories during sleep, prioritizing the retention of these emotional memories, which may be of greater future relevance than neutral memories and thus more worth remembering, according to investigators.

Over the past two decades, neuroscientists have gained increased understanding of how sleep boosts and stabilizes memories in the human brain. In the current study, researchers presented 57 healthy volunteers with a series of neutral and negative images. While staring straight ahead, the volunteers saw all of the negative images on one side of their field of vision (left) and all of the neutral images on the other side (right). Because the brain processes visual information in the opposite hemisphere from where it is viewed, this method allowed researchers to “tag” one hemisphere with negative content and the other with neutral content, thus enabling them to track localized memories. Participants were then shown the previously seen images for memory tests, with some of the images shown immediately after the learning phase and the rest shown after a period of wakefulness or sleep. During all memory tests, volunteers viewed the images directly in front of them, rather than to either side, and researchers asked participants to state whether an image had originally appeared to the left or right.

Participants who stayed awake in between memory tests forgot some of the original image locations, but forgetting was similar for neutral and negative images. Participants who slept between tests, on the other hand, had a much better rate of recall for the negative images than for the neutral ones. EEG recordings made during the learning phase show that the brain has encoded the distinct types of memories in its two hemispheres, with the negative images strongly encoded in the hemisphere opposite to the side of presentation. Researchers are now analyzing data that they hypothesize will show that the waking EEG pattern corresponding to emotional memories is the same pattern that is reactivated most strongly during sleep.

“This [finding] would provide a long sought-after brain-based explanation of how sleep selectively stabilizes emotional memories,” said lead author Roy Cox, PhD, research fellow in psychiatry at Beth Israel Deaconess Medical Center in Boston. “Our research substantially advances the notion that sleep plays a fundamental and complex role in the offline reorganization of waking experiences.”