Our brain selectively reactivates bad memories during sleep, according to new research presented at the Neuroscience 2017 conference. This is perhaps negative memories offer greater future relevance and lessons and thus more worth remembering,

Over the past two decades, neuroscientists have developed an understanding of how sleep boosts and consolidates memories. Studies show that sleep promotes the retention of episodic memories, but prioritizes the consolidation of memory depending on their perceived relevance.

Typically, emotional episodes are remembered better than neutral episodes after a period of sleep.

The study

Researchers in this new study tried to determine of whether aspects of the emotional memory are preferentially consolidated. They presented 57 healthy participants with a series of neutral or negative images.

Whiles staring straight ahead, the participants are shown all of the negative images on one side of their visual field, and all of the neutral images on the other side. Because visual information is processed in the opposite brain hemisphere from where it is viewed, this allows researchers to tag and track localized memories.

Participants then took memory tests, with some images shown immediately after the first showing, and the rest after either a period of sleep or wakefulness. During the memory tests, participants viewed all the images in front of them rather than from one side. Researchers also asked the participants whether the images had appeared originally on the right or left side during the tests.

Findings

Participants who stayed awake between memory tests forgot the locations of some of the images, but forgetting is similar for both negative and neutral images.

Participants who slept between the memory tests, on the other hand, had much better rate of recall from the negative images.

Electroencephalography (EEG) brain recording taken during the first image showing demonstrated that participants’ brain had indeed encoded the memories, with stronger encoding from the negative memories. Researchers are now analyzing these data, hypothesizing that the result would provide brain-based explanaton of how sleep selectively consolidates emotional memories.

The annual conference of the Society for Neuroscience, the largest international organization of scientists and physicians in the world devoted to understanding the brain and nervous system, was held in November, this year.