An improper transfer from the hippocampus to the dorsolateral prefrontal cortex can lead to PTSD.
A new study in Nature Communications, published on October 21, 2024, sheds light on how the brain fear memory processing, revealing why humans often struggle with forgetting traumatic events, while simultaneously finding it difficult to recall them clearly. Led by a team of researchers from Sony Computer Science Laboratories, Inc., ATR Computational Neuroscience Laboratories, and the University of Tokyo, the article explores how fear is stored in the brain and why some individuals are more susceptible to conditions like posttraumatic stress disorder (PTSD).
The research team conducted experiments using functional Magnetic Resonance Imaging (fMRI) alongside machine learning techniques to analyze how the brain responds to fear-inducing events. Participants experienced simulated threatening scenarios, such as car accidents, while their brain activity was monitored. The results demonstrated that, immediately following a fearful event, the brain creates broad, generalized memories of fear. These are known as associative memories, and during this time, the brain doesn’t necessarily focus on the exact details of the event but rather generalizes the fear response across various triggers.
Interestingly, over time, the team observed that the nature of these fear memories changes. The study found that by the next day, the brain starts to process fear in a more organized manner. The dorsolateral prefrontal cortex (the region of the brain associated with planning and decision-making) takes over from the hippocampus, which initially handles memory encoding. The dorsolateral prefrontal cortex integrates the specific sequence of the event into memory, making it episodic and less generalized. This process helps reduce the scope of the fear and the likelihood of responding to unrelated cues with the same intensity of fear.
However, the study also highlighted that not everyone experiences this transition smoothly, and this is because brain chemistry and mental wellness can differ from person to person. Individuals who suffer from anxiety disorders, particularly those at risk for developing PTSD, often have difficulty with this integration process. Their brains show weaker connections between associative and episodic memory systems, which may cause them to continue reacting to a wide range of fear-related triggers. This inability to create time-specific memories leaves these individuals trapped in a state of heightened fear and anxiety, even when the original event is in the distant past.
For those with PTSD, the memory of the traumatic event remains highly associative, meaning that anything remotely related to the trauma can trigger a fear response. This phenomenon could explain the overwhelming and intrusive memories that individuals with PTSD frequently experience, as their brains fail to associate the fear to a specific time and context.
Dr. Ai Koizumi, another senior researcher involved in the study, highlighted that these findings could lead to new and more effective treatments for PTSD. The research suggests that future interventions may be able to target the brain’s ability to integrate episodic memories more effectively, which could help in reducing the overwhelming fear responses that characterize PTSD. Understanding the mechanisms behind how fear memories are formed opens up potential avenues for therapeutic approaches that focus on strengthening the dorsolateral prefrontal cortex’s role in processing and integrating traumatic experiences.
This study offers a deeper understanding of the complexities of fear memory processing, showing that the brain doesn’t simply store fear in one way but rather transitions between broad and detailed memories over time. It holds real-word implications for the future of mental health care. By improving scientific understanding of how the brain handles fear, the medical field may be able to develop more targeted and effective treatments for those struggling.
Sources:
Study reveals mechanism behind fear memory processing
Time-dependent neural arbitration between cue associative and episodic fear memories
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