How does trauma typically affect the function of the hippocampus, and what is the direct consequence of this alteration?

Trauma typically impairs the function of the hippocampus, a brain structure critical for forming and consolidating explicit memories, which are memories of facts and events. During a traumatic event, the stress response floods the brain with cortisol and other stress hormones. High levels of these hormones can interfere with the hippocampus's ability to encode and organize memories effectively. Specifically, the hippocampus may shrink in size and exhibit reduced activity. The direct consequence of this impaired hippocampal function is fragmented and poorly organized memory encoding. This means that traumatic memories may not be stored as coherent narratives with a clear timeline, context, and emotional regulation. Instead, they can be experienced as intrusive flashbacks, sensory fragments (smells, sounds, images), and intense emotional responses that feel disconnected from the original event's context. The individual may struggle to recall the event in a chronological order or integrate it into their autobiographical memory, leading to a sense of reliving the trauma in the present moment. The hippocampus's dysfunction contributes to the characteristic symptoms of post-traumatic stress, such as intrusive memories, nightmares, and difficulty distinguishing between past danger and present safety.