A group of researchers has constructed an experiment to examine how emotional experiences affect the formation of memories. It’s already well-documented that emotional experiences are not only more likely to be recorded in memory, but emotional events also affect unrelated memories, strengthening the recall of unassociated events that happened just before the emotional surge. The new study looks at the flipside of that—how long an emotional event affects memory after the stimulation ends. This is a relatively unexplored area of research.

To find out, the researchers constructed a test using an fMRI. One group of participants was exposed to emotional stimuli for about 23 minutes, followed by a nine-minute rest, followed by a 23-minute period with emotionally neutral stimuli. The second group had these experiences reversed: a neutral period followed by a rest and then some emotionally charged experiences. The final group simply had two emotionally neutral periods with the same gap between them.

The researchers hypothesized that the emotional period's influence on memory would last into the neutral period. If this is correct, the first setup—emotional then neutral—should trigger improved memory during the neutral period. The other two arrangements, however, shouldn’t have this effect if the researchers’ hypothesis is accurate.

Results

The researchers started by measuring the skin conductance levels during the trials as an extra way to track the participants' emotional arousal. They expected it would be higher during the neutral period due to the carry-over of earlier emotional experiences. This turned out to be correct.

Depending on how long the effect of emotion on memory lasts, the subjects' memory of the events experienced during the following neutral period might also be increased. This was tested by a surprise quiz about what happened during the neutral period, taken six hours later. The results of the quizzes generally agreed with those of the skin conductance tests. Participants’ memories of what happened during the neutral period was somewhat greater when it was preceded by an emotional period. This match isn’t as consistent as the skin conductance results, but there was a clear trend nonetheless.

Additionally, the authors predicted there should be greater coordinated activity among the brain regions that support emotional memory, such as the amygdala and the anterior hippocampus. The fMRI results showed that there is greater connectivity between these brain regions during emotional stimuli, and it carries over to the neutral period.

Conclusions

“Taken together, these results provide evidence that emotional brain states […] can carry-over and become reinstated tens of minutes later when participants encountered unrelated, neutral information,” the researchers write in their paper.

The researchers note that it’s not clear which aspects of their experiment are necessary to see the same results. For example, their use of 23-minute blocks of time is arbitrary. Based on the experiment design, it's impossible to tell how long emotions' effects on memory carry over.Another unknown is whether the participants were consciously using strategies to help them remember events, and whether that played into the results. Future work may address these questions.

Nature Neuroscience, 2016. DOI: doi:10.1038/nn.4468 (About DOIs)