Those close to the World Trade Center on Sept. 11, 2001 have, on average, more vivid memories of the terrorist attacks than do those who were in other parts of New York City on that day, according to a study by researchers at New York University. The results, reported in the most recent issue of the Proceedings of the National Academy of Sciences, indicate personal involvement may be important in engaging the amygdala when recalling 9/11 events. The amygdala is a small, almond-shaped brain structure known to mediate emotion’s influence on memory.
The research team, from the laboratory of NYU Professor Elizabeth Phelps, included NYU post-doctoral fellow Tali Sharot, the study’s lead author, and contributing authors Mauricio Delgado, now at Rutgers University, and NYU graduate student Elizabeth Martorella.
"Although all of the study’s subjects were in Manhattan on 9/11, the recollections of those who were in lower Manhattan, closer to the World Trade Center, were described as more vivid, detailed, and confident than those who were further away," said Phelps. "The downtown subjects also reported seeing, hearing, and smelling what had happened. Subjects who were, on average, around midtown Manhattan reported experiencing the events second hand, such as on television or the Internet. It is clear from these recollections that proximity to the World Trade Center changed the nature of the experience of these events, such that those subjects who were downtown on 9/11 had greater personal involvement with the consequences of the terrorist attacks. As a result neural mechanisms that underlie the emotional modulation of memory were selectively active when these subjects recalled their experiences."
The findings also raise questions about the psychological concept "flashbulb memory." The concept, originally based on findings of people’s memories of the assassination of John F. Kennedy and other world leaders, maintains that unique mnemonic processes are involved in creating memories for shocking, public events. Flashbulb memory posits that, similar to a camera's flashbulb, the surprising and consequential nature of these events triggers a mechanism that conserves what occurred at that instant, producing a picture-like representation, commonly called a "flashbulb" memory. It was later found that flashbulb memories are not necessarily more accurate than other memories, but they are exceptionally vivid and held with a strong feeling of confidence.
"Our findings on 9/11 memories indicate that personal involvement may be critical in producing memories with the characteristic qualities of flashbulb memories," said Sharot. "We think this is because the amygdala, which is known to play a role in enhancing the feeling of remembering for emotional material, is more engaged when these events are experienced first hand."
METHODOLOGY AND FINDINGS
The study, conducted approximately three years after the 9/11 terrorist attacks in Manhattan, included 24 participants who were in New York City on that day. Participants’ brain activity was observed using functional magnetic resonance imaging (fMRI) while they recalled autobiographical memories from 9/11, along with other distinct, autobiographical events from the summer of 2001. The latter served as baseline memories for evaluating the nature of 9/11 memories. After the MRI scanning session, subjects were asked to rate their memories for vividness, detail, confidence in accuracy, arousal, and valence. These ratings indicated the qualitative nature of the recollective experience. Participants were also asked to write down their personal memories. Only half of the subjects reported greater vividness, confidence, and detail when recollecting events from 9/11. An examination of the experience of these participants on 9/11 revealed that they were closer to the World Trade Center on that day. Participants closer to the World Trade Center also included more specific details in their written memories, and were more likely to report first-hand experience with the terrorist attacks.
The fMRI results were consistent with the behavioral responses. Neural circuits previously shown to be related to an increase in the recollective experience of emotional stimuli learned in a controlled laboratory setting were engaged during the retrieval of 9/11 memories in subjects who were close to the World Trade Center on that day. Specifically, an increase in amygdala activity during retrieval of 9/11 events was correlated with the participants’ proximity to the World Trade Center.
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