An innovative study, to be published in Nature Communications on October 21, 2024, reveals the mechanism behind two seemingly contradictory effects of fear memories: the inability to forget yet the difficulty to recall. Led by researchers from Sony Computer Science Laboratories, Inc., ATR Computational Neuroscience Laboratories, and the University of Tokyo, the study shows how fear experiences are initially remembered as broad, associative memories, but over time become integrated into episodic memories with a more specific timeline.
The researchers conducted experiments using functional Magnetic Resonance Imaging (fMRI) and machine learning algorithms to track brain activity as participants experienced simulated threatening events, such as a car accident. They found that immediately after a fear-inducing event, the brain relies on associative memories, generalizing the fear regardless of event sequences. However, the following day, the dorsolateral prefrontal cortex takes over a role initially led by the hippocampus to integrate the event's sequence into fear memory, reducing the scope of fear.
The study also highlights that individuals with high anxiety, who are at greater risk for PTSD, may struggle with this memory integration. Their brains show weaker integration of time-based episodic memories through the dorsolateral prefrontal cortex, which may lead to persistent, overwhelming fear linked to associative cues. This insight opens new avenues for PTSD interventions by targeting the brain's ability to integrate episodic memories after trauma.
"Our findings reveal a previously unknown phenomenon in how the brain prioritizes and processes fear memories", said lead author Dr. Aurelio Cortese from Advanced Telecommunications Research Institute (ATR). "This time-dependent rebalancing between brain regions may explain why some individuals develop PTSD while others don't", explained the last author Dr. Ai Koizumi from Sony Computer Science Laboratories, Inc.
The study's findings have the potential to reshape our understanding of PTSD and fear memory processing, offering novel perspectives for developing more effective interventions.
