As time passes, newer, happier experiences gradually replace older, more traumatic memories. This is called 'memory extinction'. A study, published in the journal Neuron, has shown a gene known as Tet1 is critical to the process of memory extinction. Improving the expression of Tet1 may benefit people with post-traumatic stress disorder (PTSD), the researchers believe.
Professor Li-Huei Tsai, director of the Picower Institute for Learning and Memory at MIT, told Discovery News: 'Once a fear memory is formed, to extinguish that memory a new memory has to form. The new memory competes with the old memory and eventually supersedes the old memory'. It is thought this process is disrupted in people with PTSD.
To investigate the role of Tet1 in memory extinction, Professor Tsai and her team studied mice with the Tet1 gene knocked out. The researchers conditioned the mice to fear a particular cage where they received a mild electric shock. Once conditioned, the mice were put in the cage but not shocked by the researchers. After time, mice with regular Tet1 levels lost their fear of the cage; the Tet1 knockout mice did not.
Lead author Dr Andrii Rudenko explained that mice lacking Tet1 could not forget about the electric shock: 'They don't relearn properly. They're kind of getting stuck and cannot extinguish the old memory'.
The team believes Tet1 regulates memory extinction by controlling the expression of a handful of other 'memory genes'. This is achieved by removing DNA methylation.
High methylation levels on DNA prevent genes from being switched on, and lower levels allow the genes to be expressed. The research team observed that mice without Tet1 had very high levels of methylation on important memory genes. This makes it very difficult for mice lacking Tet1 to ‘switch on’ their memory genes to replace a traumatic memory.
Researchers hope this research will lead to new treatments for PTSD and other anxiety disorders, although this will likely take more than a decade.
British mental health charity, Mind, estimates that around three percent of the general population is 'likely to be affected by PTSD at some point'.