New research has shown that animal brains may not be able to keep up with the creation of a 'fear memory' – which could be the reason post-traumatic stress disorder (PTSD) and other similar conditions occur.
This could help researchers finally understand why PTSD occurs in a subset of the population, while others are unaffected, and why it is so difficult to treat.
PTSD can occur after someone is exposed to a traumatic event. It can be a harrowing condition for both the person and their family and although there are promising drugs on the way, currently the treatments are limited.
So researchers from the University of Technology Sydney (UTS) and the Garvan Institute, both in Australia, investigated how memory formation of traumatic memories occurs, to gain some insight into how we could stop it.
The team split up 80 mice into separate groups, and tested if rapidly inducing fear into the animals (via a 1 milliamp shock to the foot) caused a complete memory to form.
Bryce Vissel, one of the researchers and a neuroscientist at UTS, says the results suggest that the animals may be able to form strong fear memories very quickly, but their hippocampus cannot form a complete picture and the details of the event to go with it.
"This could be significant because animals rely on their memory of where, when and how the traumatic event occurred to determine when they should be fearful in future," Vissel said.
"If they form an ambiguous memory that lacks the detail necessary to tell different environments or situations apart, they may trigger the traumatic memory in a variety of inappropriate circumstances."
The researchers think that this disconnect could lead to abnormal fear-related behaviours in mice – similar to how we see triggers occur in these types of disorders in humans.
There are a range of reasons people get PTSD, such as whether you're a child or an adult, genetics, and the type of trauma experienced, but none of these things fully answer why some people get PTSD in traumatic situations and some don't.
"Traditionally, memory disorders have been investigated and treated by focusing on the idea that memory recall is faulty," said Raphael Zinn, one of the researchers.
"However, if part of the problem lies in how the memory was formed in the first place, research and treatments may need to focus not only on how the memory is recalled but also on how it was originally formed,"
Although this research is promising, it's important to note that the tests were completed in mice, and we can't make any definitive statements until after we've been able to investigate this in humans.
However, this early research is an exciting step forward – the team are hoping to start examining brain mechanisms that could be used to repair and help those with the disorders.
The research has been published in the journal Learning and Memory.