Trauma Appears To Alter How We Process Memories

Trauma can leave traces that long outlive the memory of the event.

They can wreak havoc on the body. They can mess with the immune system, sparking inflammation. Some research has suggested it can contribute to autoimmune disorders such as multiple sclerosis. It can cause muscle pain, interfere with a good night’s sleep, and drive up blood pressure.

But where post-traumatic stress disorder (PTSD) typically leaves its most painful scars is on the brain. It can dramatically alter the forming and processing of memories. More specifically, it can shape how the brain sorts – and prioritizes – different memory types.

Now, new research – published this week in Nature Communications – exposes some of the mechanisms that power this phenomenon. A group of researchers found that, after a traumatic event, the brain strengthens cue-threat associations while undermining episodic memories. This shift in memory prioritization appears to evolve, particularly during sleep. The data could help explain the memory dysfunctions common in PTSD patients.

“This time-dependent rebalancing between brain regions may explain why some individuals develop PTSD while others don’t,” Sony Computer Science Laboratories Inc. researcher Ai Koizumi, PhD, explained in a press release. Koizumi was part of a team that also included researchers from ATR Computational Neuroscience Laboratories and the University of Tokyo

Methodology

To determine how the brain encodes cue-threat associations and the sequence of events during a simulated traumatic experience, the research team came up with a unique threat-conditioning model. The researchers exposed study participants to cues – such as the sounds one normally hears in a traffic accident – in a particular order, followed by a car crash, which served as the traumatic event. This allowed the team to observe how memories of individual cues and the sequence of events competed for dominance.

Immediately after the traumatic event, simple cue-threat associations overshadowed the participants’ memories. For example, participants would experience fear in response to a specific sound (a bell or horn) that had been associated with the accident but struggled to recall the precise sequence of events.

Checking back in 24 hours, the researchers stumbled onto a transformation. The participants’ fear responses had refocused on the sequence of events. This, the researchers argued, suggests that their memories had reorganized overnight from a generalized cue-based fear to a more precise episodic fear memory.

Digging Deeper into Trauma

Leveraging multivariate functional MRI (fMRI) to track the communication between different areas of the brain, the researchers found that this migration from generalized to specific fear memory involved changes in how different brain regions interact with one another.

In the immediate aftermath of the traumatic experience, the hippocampus played a significant role in communicating threat-related information to the prefrontal cortex. But a day later,  the dorsolateral prefrontal cortex (DLPFC) took over, helping to shape more specific, sequence-based memories.

The researchers found that this (almost literal) overnight transformation failed to take place in individuals with heightened trait anxiety, a known PTSD risk factor. Those with high anxiety levels didn’t demonstrate that same move toward more precise episodic memories. Instead, their brains maintained a reliance on generalized cue-threat associations.

These results could offer a potential explanation why PTSD patients typically struggle with overgeneralized fear and fragmented memories of traumatic events, and are unable to recall the specific details of the event.

The research also highlighted the importance of time in the way the brain processes traumatic memories. The study’s findings suggest that the brain initially prioritizes generalizable associative memories immediately following a traumatic event, likely as a survival mechanism to help individuals quickly respond to potential future threats. However, as time passes – particularly with the help of sleep – these memories are refined into more detailed, episode-based memories that can help individuals better contextualize their fear responses.

Revelations Could Inform Better Trauma Treatment

The findings provide an integrated account of how two types of memory dysfunction – strengthened cue-threat associations and weakened episodic memory – might manifest in PTSD.

More importantly, the data suggest new treatment approaches, including a strategy that targets the brain’s natural process of memory reorganization during sleep. This could help PTSD patients recover more coherent memories of their experiences.

Finally, this new research offers critical insight into how the brain processes traumatic memories, documenting how memory systems compete for dominance in the aftermath of trauma. It also highlights how important time and sleep are in processing these memories. This could have huge implications for understanding and treating memory dysfunctions in PTSD patients.

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.

Further Reading

Disaster Surge Highlights Need For Better Mental Health Support

Study Finds Brain Network That Could Protect Against PTSD

Can Emotional Dysregulation Help Explain Adolescent PTSD?