The old brain, humans’ lower brain structures involved in the limbic system (the ‘lizard brain’) is constantly scanning the environment looking for any changes that signal danger, food or sex.
A major job of the old brain is to keep us from harm, anything threatening our survival will get our old brain’s attention. The threat does not even have to be directed at us. Even watching a movie or an ad (not a real situation) of someone else in hard will set off alarm bells in the old brain. Anything that happens when we are on high alert is processed deeply and emotionally in our memory. We pay attention to anything that happens when we are in an emotionally arousing situation. We also remember it more deeply.
E,g. Using imagery that elicits danger, food or implies sex.