Professor Steve Gentleman poses with a human brain at the Multiple Sclerosis and Parkinson’s UK Tissue Bank at Imperial College London, June 3, 2016. Reuters/Neil Hall

Beyond the biological fact of billions of neural connections in the brain, how human memory works is poorly understood. A new study by researchers from New York University (NYU) sheds some light on the effect emotional experiences have on how experiences are remembered by the brain.

“How we remember events is not just a consequence of the external world we experience, but is also strongly influenced by our internal states — and these internal states can persist and color future experiences,” Lila Davachi, an associate professor in NYU’s Department of Psychology and Center for Neural Science and senior author of the study, said in a statement.

Emotional experiences are better remembered than non-emotional experiences, but the study showed that even non-emotional experiences immediately succeeding emotional events were better remembered on later memory tests.

“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,” Davachi said.

To arrive at their findings, the researchers took two groups of test subjects and showed them two sets of images. One group was first shown images that evoked emotional arousal, and then, 10 to 30 minutes later, the other set of ordinary, emotion-neutral images. The other group of test subjects was shown the two sets of images in the reverse order, the neutral images first and the emotional ones later.

Both groups were given a memory test six hours later to see how well they recalled the images they had seen. “The results showed that the subjects who were exposed to the emotion-evoking stimuli first had better long-term recall of the neutral images subsequently presented compared to the group who were exposed to the same neutral images first, before the emotional images,” the statement said.

Based on brain activity, measured using functional magnetic resonance imaging (fMRI), researchers found that brain states elicited by emotional activity persisted for about 20 to 30 minutes after the experience and therefore affected the way the test subjects related to and remembered non-emotional events that followed soon after.

The study detailing the “emotional hangover” was published Monday in the journal Nature Neuroscience under the title “Emotional brain states carry over and enhance future memory formation.”