- Memory creation is a complex brain process that involves storing and retrieving information.
- Memories can be positive or negative. However, the overactivation of negative memories may play a role in mental health conditions, including post-traumatic stress disorder (PTSD), depression, and anxiety.
- Experts believe that identifying and manipulating fear-based memories may lead to effective treatment options for people living with these conditions.
- Recently, researchers from Boston University found that positive and negative memories are distinct in several ways.
- These differences may make it possible in the future to target negative memories responsible for fear-based mental health conditions.
Memory is a complex neurochemical process of storing information in the brain. Memories consist of images, thoughts, and emotions based on what a person saw, heard, or experienced. In addition, an individual can perceive memories as positive or negative depending on how the brain processes them or the nature of the experience.
Yet when negative memories become recurrent or intrusive, they can lead to several mental health conditions, including depression, anxiety, or post-traumatic stress disorder (PTSD). People living with these conditions often experience intrusive fear-based thoughts or reoccurring memories of an actual event.
Identifying the process and location of negative memory storage in the brain may help scientists understand better ways to treat these conditions.
Recently, researchers at Boston University found more clues about where and how memories are stored in the brain. Using mice, the research team discovered that positive and negative emotional memories reside in distinct areas in a brain region called the hippocampus. Moreover, each type of memory communicates to other cells through different pathways in the brain.
The researchers say that this positive and negative memory mapping could help scientists target negative memories and lessen their impact on someone with fear-based mental health conditions.
The study appears in the journal Communications Biology.
The building blocks of memory
Memories are stored in the brain as cell groups called engrams. Engram cells activate during a learning session and are modified by aspects of the experience. Moreover, these neural cells reactivate to retrieve this stored information in the future.
Additionally, recent research has identified engrams in specific brain regions, including the hippocampus, amygdala, and cortex. The study also revealed that engrams for a single memory appear over multiple areas in the brain.
Furthermore, the Boston University team’s previous research in mice found that reactivating positive memories disrupted fear-based memories, making them less impactful.
The current study focused on the hippocampus, a part of the brain that processes learning and memory.
Investigating engrams in the hippocampus
Based on their earlier findings, the researchers sought to understand more about how positive and negative memories reside in the hippocampus. The scientists also wanted to characterize the molecular and cellular identities and behaviorally relevant functions of the hippocampus cells that process positive and negative memories.
For the experiment, the researchers used optogenetic methods consisting of activity-dependent viral constructs and optical fiber implants in mice. These methods allow scientists to modify brain cell receptors to respond to light and appear as different colors in fluorescent images.
The scientists then exposed the mice to stimuli, including reward sessions and fear exposure to induce positive and negative memories.
Using imaging techniques to examine the color codes of these memories, the scientists discovered that positive or negative emotion-based memory engrams are different in several ways.
They found that each type of engram is distinctive and stored in separate areas in the hippocampus. They also appear to be unique on a molecular level and use different pathways to communicate with other cells.
In a Boston University article, the study’s co-author Dr. Steve Ramirez, an assistant professor of psychological and brain sciences at Boston University College, notes “that’s pretty wild, because it suggests that these positive and negative memories have their own separate real estate in the brain.”
“We now have a bunch of markers that we know differentiate positive from negative in the hippocampus,” Dr. Ramirez says in the article.
What are the implications of these findings?
As scientists gain more understanding of how different types of memories are created and reactivated in mice, these discoveries could eventually lead to new treatments for fear-based mental health conditions in humans.
After reviewing the study results, Dr. James Giordano, a Pellegrino Center Professor of Neurology at Georgetown University Medical Center, Washington, told Medical News Today:
“Negative memories can contribute to the development of a number of anxiety disorders, including specific phobias, […] depressive disorders, and certain aspects of personality types and disorders. While these results were obtained utilizing a mouse model, they are important to help develop and guide molecular neural imaging approaches that could be useful in assessing whether positive and negative memories are encoded within distinct neuron populations in the human hippocampus.”
Dr. Giordano explained that the identification of these distinct populations of positive or negative memory neural cells may be useful in currently available and newly emerging therapies.
“For example, certain types of indwelling brain stimulating technologies could target discrete populations of the cells to differentially modulate positive or negative memories,” he said.
Moreover, “understanding the anatomical distribution of these distinct nodes of cells might be useful in developing novel applications of transcranial magnetic and/or electrical stimulation,” Dr. Giordano concluded.
Dr. Tamika Haynes-Robinson, a neuropsychologist at Orlando Health, told MNT that “[m]ood disorders including bipolar disorders, personality disorders as well as psychotic disorders including schizophrenia can be heavily influenced by repeated exposure to negative events and the memory of these events.”
After reviewing the study findings, Dr. Haynes-Robinson said that “this research is instrumental evidence of a long-standing theory of how we process emotions and behave as well as underpinning theory on [the] psychopathology of mental health disorders such as depression and anxiety.”
“Repeated fear-based or aversive stimulation drives anxiety and depression just as positive experiences drive our reward system. Understanding how these pathways work in our brain can help drive innovative therapies that may target these pathways to minimize the overactive aversive response that is behind anxiety and PTSD as well as depression,” she explained.
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