1) Intrusive imagery and sensations, almost as if a movie is playing in your head.
2) Cognitions and cognitive processes; this is how you make sense of the event and all the facts/context might not be taken into account.
3) Negative affect and arousal which can lead to dysregulation of prefrontal cortex (executive planning center in brain) and stress hormones.
4) Escape and avoidance behaviors.
CPT helps you approach the memories, thoughts, and feelings about the trauma that have been avoided to help the interpretations become more realistic. The goal is to change your belief structure to incorporate the trauma in a more realistic and balanced way.
There is a natural response to a scary situation: flee, fight, freeze. The hypothalamic-pituitary-adrenal axis is activated, sending the necessary hormones such as cortisol, to put a body on hyper-alert to manage the situation. Your amygdala (fear center in the brain) sends an alarm signal to your brain stem to also prepare you for danger. The brain stem activates neurotransmitters to alert your prefrontal cortex. When you are faced with PTSD, you develop such strong conditioned responses to trauma reminders that your prefrontal cortex may shut down, thus no longer sending a message back to the amygdala that everything is again safe. Your amygdala becomes dysregulated and hyper-responsive. It is only natural that you engage in escape and avoidance behaviors (including alcohol or substance use or avoidance of similar environments).
CPT has you talk and write through the trauma experience, providing techniques to help prevent the prefrontal cortex from going completely off-line. This allows evidence to be received that more accurately reflects both the trauma and current environments. Two common cognitive errors are assimilation (taking in only some of the data to remain congruent with pre-existing beliefs) and over-accommodation (seeing all future experiences through the lens of the trauma). You explore contextual information important to effective trauma processing to better take in all the facts and recognize that a single event doesn't necessarily lead to many events. Important data include the chronology of events, the environment in which the trauma occurred, presence of others and their roles and abilities, and your mental state and abilities at time of trauma.
In summary, CPT, in a structured and compassionate way, helps you to approach that which you have avoided. When engaged in escape and avoidance, your life can become very narrow. Learning tools to challenge cognitive errors and modulate negative emotions and the stress response allows you to approach these memories in a new way, allowing for recovery through accommodation: how to now live your life with this past traumatic experience as a component of your history.