New MQ-funded research has found that re-writing memories, rather than suppressing them, could be the most effective way to overcome PTSD.
In a first for mental health science, MQ Fellow Johannes Gräff has pinpointed the cells vital for reducing traumatic memories - offering hope for testing new interventions.
It’s estimated that almost a third of people will suffer from a fear or stress-related disorder at one point in their lives.
Post-traumatic stress disorder (PTSD) is one of these – an anxiety disorder caused by frightening or distressing events. Memories of these events can be so deeply ingrained that someone with PTSD might relive the trauma through flashbacks, experience feelings of isolation and irritability, or have problems with sleep and concentration. For the same reason PTSD is difficult to treat – and these symptoms can have a significant impact on someone’s day-to-day life for years following the traumatic event.
Current treatments for PTSD include medication and psychological therapies such as cognitive behavioural therapy and exposure therapy - the practice of getting people to overcome their fears by facing them in a safe, controlled environment. But because scientists don’t understand exactly how the brain stores memories, there is ongoing debate about the most effective way to reduce the severity of the traumatic memories: to suppress memories of the event, or to rewrite them?
In 2015, MQ-funded researcher Johannes Gräff set out to identify precisely what happens in the brain during re-exposure to frightening events. His study, published in the journal Science, uncovered the group of neurons (brain cells) involved in rewriting traumatic memories. His results support the notion that re-writing memories – by ‘reliving’ fears – could be the most successful way to overcome a trauma.
Johannes and his team worked with mice which were genetically modified so their neural activity could be measured. They focused on the neurons in an area of the mice’s hippocampus called the dentate gyrus – part of the brain that’s involved in processing and recalling memories.
First, they trained the mice to fear a small box, by giving them mild electric shocks when they were inside. After this, the mice underwent fear-reducing training, also known as extinction, which resembles exposure therapy in humans. The first time the animals returned to the box, they froze. But as the mice were repeatedly confronted with the box, which now no longer gave them electric shocks, their fear gradually began to subside.
The researchers monitored the neurons that were activated throughout this process. They saw that the neurons in the dentate gyrus which became active when the mice first recalled the traumatic memories were still active when the mice no longer showed fear. Furthermore, the less scared the mice became, the more the same neurons were reactivated – suggesting that the neurons that recall fear may also be vital in working through that fear to reduce traumatic memories.
To try and prove this theory, the team silenced the mice’s recall neurons with drugs, stopping them from being reactivated when the mice were exposed to their fear during therapy. This prevented the mice from responding as well to the fear exposure therapy.
In contrast, when the team boosted the activity of the recall neurons, the mice overcame their fears quicker than before. From this, Johannes and his team concluded that decreasing the impact of fearful memories is dependent on the continued activity of the neurons in the dentate gyrus.
So what does this mean?
Well, it suggests that effective recovery from PTSD is more likely to result from rewriting memories, rather than trying to rationalise or suppress them. It’s an argument for bravery vs retreat – facing fears rather than burying them. It’s also helped scientists to pinpoint the cells that are important for reducing traumatic memories, opening the gates to test new, more refined interventions.
We spoke to Johannes to ask what this work means for the future – and why it’s hopeful:
“Our results confirm experimentally what has been known empirically from psychology for a long time: that it’s better to face your fears than to avoid them. That is because the same cells that were important for storing the fearful memory are the key to unlearning the fearful memory as a safe one. These results are a first, crucial step in better understanding the attenuation of long-lasting traumatic memories, for which very little is known.
Now that we have pinpointed the cells that are important for the extinction of long-lasting traumas, we finally have a handle to better understand this process at the molecular level. Current efforts in the lab are aimed at deciphering which genes inside these cells are driving the attenuation of the traumatic memories, which may in the long-run inspire the development of new and better medical approaches against these devastating memories.”
Last updated: 3 December 2018