SALT LAKE CITY - Americans aren't having nightmares-or dreams of any kind-that replay the 9/11 attack on New York, according to sleep researchers.
SALT LAKE CITY, June 20 - Americans aren't having nightmares-or dreams of any kind-that replay the 9/11 attack on New York, according to sleep researchers.
That is not to say that Americans are ignoring 9/11 in their dreams, said psychiatrist Ernest Hartmann, M.D., of Tufts, in Boston. Instead, the 9/11 event has had the effect of increasing the intensity of imagery in dreams that superficially have nothing to do with airplane attacks on downtown New York.
The intensity of the so-called "central image" of a dream is correlated with the strength of the emotions that underlie the dream, Dr. Hartmann said at Sleep 2006, the joint meeting of the Sleep Research Society and the American Academy of Sleep Medicine.
The example he gave was that after 9/11 the tidal wave that sweeps one away in a dream is more intense than it was before 9/11. On the other hand, it remains a tidal wave-not a replay of a TV image of an airplane attack on a building.
Dr. Hartmann and colleagues have performed a range of studies, showing that concept of dream imagery. In one study, for instance, he and colleagues showed that students who reported earlier physical or sexual abuse tended to have dreams whose central image was much more intense than students without such a traumatic history.
But such studies are not systematic, he said, in that they do not involve a common event. "We tried to do a systematic study, using the events of 9/11, which presumably produced at last some signs of trauma in all of us," Dr. Hartmann said.
The researchers found 44 people-60% of them female-who have routinely recorded their dreams for years and asked them to submit the records of the last 10 dreams before the 9/11 attacks and the first 10 dreams afterward. The ages of the respondents ranged from 25 to 69.
Dr. Hartmann and colleagues analyzed the reports, on a blinded basis, scoring each of the 880 dreams for intensity of central image, the emotion pictured by the central image, its length, its dreamlike quality, and its vividness. They also looked for three elements of content-attacks, buildings like the World Trade Center or the Pentagon, and airplanes-and applied a scale of "nightmare-likeness."
The key finding, he said, was that 36 of the 44 participants had an increase in central image intensity-scored on a scale ranging from 0 to 3-after the attacks. Before 9/11, the 44 participants had an average intensity of 1.10, while afterward, it rose to 1.28, a difference that was significant at P<0.001.
There was no difference in length, dreamlike-ness, or vividness, he said, or in dreams involving buildings or airplanes. On the other hand, there was an increase in dreams involving attacks of all kinds, which was significant at P<0.01, and a marginally significant increase in nightmare quality (P<0.05).
What was missing, Dr. Hartmann said, were any direct "replays" of the events. "We all saw those airplanes hit the towers hundred of times," he said. "That never showed up in the dreams."
The study is a "very good first step in looking at how events that are very significant for a very broad segment of the population" become translated into dreams, said Anne Germain, Ph.D., of the University of Pittsburgh, who chaired the session in which Dr. Hartmann reported his study.
She noted in an interview that a great deal of research has been done on how daytime events affect dreams, but Dr. Hartmann's study differs because it uses a single common event. "9/11 has the particularity that it touched a lot of people at once," she said. "The question is, did it influence dreams in people in general who all shared this one particular event."
And what the study appears to show, she said, is that there was at least some influence: "You don't get replays of images, but you do get replays of emotions."