For the first time, scientists have identified the brain circuitry involved in the creation of “flashbulb memories”—vivid, picturelike recollections of shocking, traumatic events such as the Sept. 11 terrorist attacks—and that personal involvement in these events may be crucial in forming these memories.

New York University psychologist Elizabeth A. Phelps and her colleagues say that activation of the amygdala, the brain’s emotional arousal center, is stronger in people in close proximity to significant events than it is in those farther away, possibly because the amygdala, which enhances the memory of emotional information, is more engaged when people witness such events firsthand.

Phelps and her team studied functional magnetic resonance imaging scans of the brains of 24 people who were in New York City on the day of the terrorist attacks. Three years after the attacks, they observed the participants’ brain activity during recall of the day’s events, as well as other autobiographical events from the preceding summer. The participants, who were asked to retrieve memories of Sept. 11 while being scanned, rated their memories for vividness, level of detail, and confidence in the accuracy of the memories, and they were asked to write about their personal experience of the terrorist attacks and where they were at the time.

People who were in downtown Manhattan, near the World Trade Center, reported more vivid recollections of the attacks, including specific details about sounds and smells, than people who were a few miles away, in midtown, and experienced the event via television or the Internet.

“While all of the study subjects were in Manhattan on 9/11, the recollections of those in lower Manhattan, closer to the World Trade Center, described the attack more vividly and in more detail than those who were farther away,” Phelps says.