Human Brain Recalls Old Memories During New Experiences

According to neuroscience studies, when mice and other rodents negotiate a maze, their brain frequently “replays” key past events. This mental replaying of events, such as the path traveled to arrive at their current location, may aid rats in creating a mental map of their spatial surroundings and understanding their place within it.

University College London and Queen Mary University of London researchers recently investigated the notion that the human brain replays past events in order to make sense of developing, non-spatial experiences. Their findings, which were published in Nature Neuroscience, support this notion and show that the method by which the human brain reactivates these events is significantly more sophisticated than that reported in rats.

“We know that the brain can ‘replay’ information that was encountered in the past, although this has mainly been studied in navigation tasks involving rodents,” Avital Hahamy, one of the researchers who carried out the study, told Medical Xpress. “We also know that the human brain chunks our ongoing experience into smaller events that we can later recall as a narrative of our daily experience (e.g., your morning events might include taking the tube to work, reaching the office, going into a meeting, etc.).

“We wondered whether the human brain also replays past information to connect these different events into an overarching understanding of our experiences (e.g., allowing us to understand why a meeting started without us by linking this present event to a past event, such as the tube running late).”

Hahamy and her colleagues attempted to design an experiment that would induce the replay of past events in rodents, but during non-spatial daily situations. Finally, they chose to have their participants view a video or listen to audio recordings of a narrated story while a functional magnetic resonance imaging (fMRI) scanner recorded their brain activity.

“Movies and stories simulate real world experiences, as they are composed of events that should be linked together to understand the overall narrative,” Hahamy explained. “We developed a new fMRI method to look for replay of past information in the transitions between movie/story scenes. We basically asked—would our brains replay past information that is needed for interpreting a scene we had just perceived?”

Interestingly, Hahamy and her colleagues discovered that while participants were immersed in a movie or story’s storyline, images of past events that were required to make sense of each present scene were resurrected in their brain. In contrast to rodents, these reactivations occurred while the participants were watching the movie or listening to the story, rather than when they were resting from the job.

“We found that the same brain regions that replay spatial information in the rodent brain also replay narrative events in the human brain,” Hahamy said. “In other words, replay, previously thought to mainly support spatial navigation, could also underlie the human ability to make sense of narratives. Moreover, while research in rodents proposed that replay is used to store past events into memory, mostly when rodents rest or sleep, we suggest it can also be used to make sense of the present, on the fly, while events are unfolding.”

Overall, this team of academics’ latest study implies that as humans are attempting to make sense of their current experiences, their brain may continuously recall important prior events. These findings may soon motivate additional research aimed at better understanding this fascinating “replay” mechanism and its various functional roles.

“The brain mechanism examined in our paper is an example of a process that was widely studied in rodents but could have a richer function in humans,” Hahamy added. “It would now be interesting to study whether people suffering from clinical conditions, which are characterized by abnormal integration of information, would have a malfunctioning replay mechanism.”

Source Link