Following a significant head injury with confirmed structural brain damage, a patient has a persisting, severe difficulty forming new memories, while her sense of who she is and her social behaviour remain essentially intact and recognisable to those who know her. What is this?

This is organic amnesia: memory loss resulting from a physical disturbance of brain function, here a confirmed structural head injury, with personal identity typically less affected than in dissociative amnesia, exactly as described. It is not dissociative amnesia, which shows striking preservation of complex skills and social behaviour alongside profound memory loss, but critically involves loss of personal identity itself, which is explicitly preserved here. It is not catathymic amnesia, which is limited to a specific painful memory rather than the broader, injury-related pattern seen here. And it is not simple forgetfulness, since the memory impairment here is severe, persisting, and tied to a confirmed physical brain injury.