Memories tied with intense emotions are hard to forget. They tend to resurface now and then triggered by similar sights, sounds, or scents. We may find ourselves reliving the moment long past, as we feel the same emotions course through our body.
Any memory attached to strong emotion like losing a loved one, or what we were doing during a national catastrophe like 9/11, are hard to erase while memories of inconsequential events are hard to retain.
What makes memories of emotionally charged scenarios stay with us forever? To answer this, researchers from Columbia University: Rene Hen and Jessica Jimenez recorded the brain activity of laboratory mice.
After all, we possess limited brainpower so we only need to retain memories that may be useful to us in the future. So it makes sense that the brain filters out superfluous information.
For the research, Hen and Jimenez settled on fear as the emotion critical for our survival. Fear serves as a learning experience when the brain saves details in our neurons which may help us avoid getting ourselves in perilous situations in the future. What remains to be discovered is how these memories preserved in the hippocampus become so strong.
The hippocampus has long been known as a vital part of the brain for contextual memories. Its role has been accepted as a strictly cognitive structure involved in processing contextual and spatial information, however, lately, its role in directing emotional behavior has been brought to light as well.
The dual functionality of the hippocampus is thought to be achieved through segregation along the dorsoventral axis. The dorsal hippocampus is responsible for cognitive processes and the ventral region is mostly involved in emotional behaviors.
The researchers placed laboratory mice into new and terrifying environments and observed the activity of the hippocampal neurons that extend to the brain’s fear center: the amygdala. Neuronal activity was recorded once more a day later when the mice tied remembering the experience.
It was observed that neurons that responded to the frightful experience sent information to the amygdala. When the mice retrieved the memory a day later, the same neurons fired off in synchrony.
Jimenez commented, “We saw that it’s the synchrony that is critical to establish the fear memory, and the greater the synchrony, the stronger the memory. These are the types of mechanisms that explain why you remember salient events.”
Much about the synchronization remains unknown and questions such as how and when the synchronization takes place still puzzle researchers. Finding the answer to these, however, could help understand the inner workings of the brain and the process of creating memories that last a lifetime.
The research has far-reaching implications and could most importantly help discover new avenues of treatments for posttraumatic stress disorder. He infers that people suffering from PTSD relive the same traumatic event repeatedly triggered by similar situations because the synchronization of their neurons is very strong.
“We’re really trying to dig into the mechanisms of how emotional memories form to find better treatments for people with PTSD and memory disorders in general,” he concludes.
Jessica C. Jimenez, Jack E. Berry, Sean C. Lim, Samantha K. Ong, Mazen A. Kheirbek, Rene Hen. Contextual fear memory retrieval by correlated ensembles of ventral CA1 neurons. Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-17270-w