It has been known for a while that experiencing emotion can influence how well we remember things.
Researchers from New York University have built on this knowledge and found evidence that reacting to something emotionally — like watching a sad scene in a film — may also improve how well you remember something you've seen, and this memory boost could continue as much as 30 minutes after experiencing the emotion.
This goes against the popular theory that being emotional can actually make memories fuzzy.
A group of 115 volunteers took part in the study, which was published last month in the journal Nature Neuroscience. They were split into groups and either shown images that would trigger an emotional reaction, and then neutral ones after 10 to 30 minutes, or the other way around. Six hours later the subjects had a surprise memory test, where the researchers asked them questions about the neutral images to see how well they remembered them.
The researchers measured participants' physiological reactions using skin conductance. In healthy people, the skin momentarily conducts electricity better when we experience something physiologically arousing, so the researchers monitored this to see whether or not the subjects really were experiencing a necessary level of emotion. At the same time, the researchers used an fMRI scanner to monitor what the volunteers' brains were up to.
The researchers wanted to find out two things: first, whether people could better remember the neutral images if they were shown them before or after being triggered emotionally by the emotional images, and second, whether brain regions that support emotional memory were more active and showed more connectivity in either case.
As it turns out, those that were shown the emotional stimuli before being shown the neutral images tended to better remember the neutral images.
According to the new research, when we get emotional, the amygdala in our brain is stimulated and our bodies often secrete adrenaline. Somehow, these two processes work on the hippocampus, which is the centre of memory function, and our memories for that time period are sharpened.
Dr Lila Davachi, senior author of the study and an associate professor in NYU's Department of Psychology and Center for Neural Science, said in a statement that this is because creating memories does not just rely on the world we experience externally.
"[It's] also strongly influenced by our internal states," she said. "These internal states can persist and colour future experiences."
She added that this kind of "emotional hangover" influences how we take on board information for quite a long time afterwards.
"Emotion is a state of mind," Davachi said. "These findings make clear that our cognition is highly influenced by preceding experiences and, specifically, that emotional brain states can persist for long periods of time."
MRI images pointed towards this explanation. Brain regions such as the amygdala and anterior hippocampus are associated with both memory and emotions, and they lit up more after the emotional response, and were still engaged up to 30 minutes afterwards.
This led the team to believe that the influence of emotion on memory in these areas of the brain can persist over many minutes, which was shown by the results, but the long-term impacts remain a mystery.