Learning how to work with PTSD and traumatic memories using mindfulness has been a long interest of mine. Through learning how to apply mindfulness to painful memories and emotional reactions we can change those neural pathways quite effectively. We do this by learning to meditate on the trauma itself.
This is not what most people are familiar with when they think about mindfulness meditation; indeed most practitioners that I see focus on the breath or body sensations as a way of escaping the emotional pain and in an attempt to calm the mind. To me this is the exact opposite of what we should be doing. Avoiding painful experiences simply reinforces them and also prevents them healing.
However, through persistent training on meditating on the emotions themselves we begin to strengthen the Observer Mind, what we call the True Self in mindfulness psychology, and this effectively creates a space between you and the trauma. You learn to "sit" with the painful memory but without being pulled into it and overwhelmed by it. Establishing this kind of Mindfulness-Based Relationship (MBR) as it is called is the most important first step in healing and resolving trauma.
Another part of mindfulness therapy that I find endlessly interesting is to investigate the image structure of the emotions and the traumatic memories. Imagery is how the mind organizes emotion and emotional regulation and healing occurs when the emotional imagery changes or is changed directly through mindfulness-based image reprocessing. As we say, "when you change the imagery, you change the emotion." You can try this for yourself - just try taking the traumatic memory image and making it the size of a grain of sand. Very simple, but often immensely effective.

The Boulder Center for Online Mindfulness Therapy