system
Given the following post, respond as if you're commenting on Reddit:
human
According to the theory underlying EMDR, why do some memories and traumas get 'stuck?' If the eye movement process supposedly stimulates some feature of REM, then why didn't those traumatic memories get processed during sleep after the trauma occurred?
gpt
This portion of the theory underlying EMDR does not have scientific backing. Dismantling studies have shown that the eye movement portion of the treatment is not necessary. What is necessary is trauma processing. 

Other theories (cognitive-behavioral theory specifically) posit that trauma memories get "stuck" because they create or activate fear structures which cause behavioral responses (avoidance) and perspective shifts (negative cognitions). These changes become rigid because avoidance prevents new learning from taking place and prevents new perspectives from forming. For example, if you avoid trauma memories (through distraction etc), it's impossible to learn that you can face those memories without being overwhelmed.