First thing first - what is a flashbulb memory? It is one of those events that gets seared into your brain. Where were you when the Space Shuttle exploded? On 9/11 when the Towers fell? When Kennedy was shot? We seem to remember these events vividly, like a photograph.
Second, what is the neurospsychology behind flashbulb memories? First, we rehearse them more. That means we go over them over and over again in our mind to make sense of what happened. Did those planes really just crash in the Twin Towers, or is CNN showing a movie? These memories obviously have much stronger emotional connections than most other kinds of memory. They also become more coherent because the rehearsal tends to fill in holes. Sometimes we fill them in with our own assumptions, but we fill them in. But these memories are not wide, rich memories like the ones we get from our own personal experiences. Its just a photograph. But since they are coherent, they should be remembered better than less coherent memories are.
Research shows something interesting about flashbulb memories. You would think that we would remember them better than other memories, right? They are coherent, salient, important, vivid, etc. But it turns out, we just think we do. Studies have shown that over time, your memory of these flashbulb events degrades at about the same rate as other memories do. Maybe that coherence and vividness starts them out strong, but these things don't keep it from degrading just like all of our other memories. One thing is different though. Our confidence that we remember them accurately doesn’t go down. Even as our memories degrade, we are SURE we still remember it just the way it happened.
Of course, that refers to you and I who saw it on TV. Another study compared people who were downtown (visible out their windows) on 9/11 v people who were midtown (very close but not actually visible). Memory was much better for the downtown residents, even if they didn’t actually participate in the rescue and cleanup. For them, it was a personal experience, not a flashbulb.