Trauma definition: Noun,
A deeply distressing or disturbing experience.
Emotional shock following a stressful event or a physical injury, which may be associated with physical shock and sometimes leads to neurosis.
An event or situation that causes great distress and disruption.
Here is an example of how a past trauma influences our protagonist’s actions/thoughts in the now of the story. Back story is an important tool which can be used to give the reader a sense of the protagonist’s past, reasons for certain behaviors, and depth. It also helps the reader decide whether or not they are sympathetic to her.
Her abductor had broken her down, insinuated his essence into her very being. Soon she would be beyond help. Did she want help? She had no knowledge of the person she’d become. Everything in her screamed to escape: to never let this man touch her again. Everything in her wanted to stay and feel the call of his tremendous need, which somehow echoed in her. But his need also recalled her past, a past she’d spent the better part of her life trying to forget. She didn’t want to face it in the light of day ever again. ©2011
Does this make you want to know more, or feel sympathy for her? Notice the trauma is only eluded to in this paragraph, not described. That will come later, or might have been explained in another context in the novel. Like maybe through Alban Thain’s research? Trauma is a great tool and also serves to add drama and action to your story.