This 2014 rodent study provided evidence for a portion of the neurophysiology that underlies how painful long-lasting memories are stored and why they are so strong. The amygdala was the brain area studied.
The researchers were misguided in news coverage by focusing on solutions such as external mechanisms to forget these memories. The researchers should think in terms of how their research can help people who can help themselves instead of having something externally done to them.
After all, we’re humans who can participate in therapy, not lab rats who need to be fixed.
http://www.pnas.org/content/111/51/E5584.full “Hebbian and neuromodulatory mechanisms interact to trigger associative memory formation”