Earthquake shakes up nightmare frequency.

The October 1989 earthquake that rocked the San Francisco Bay area rattled the sleep of college students in the region for at least a month by churning up an unusually large number of nightmares, a new study finds. But students described most nightmares -- even those incorporating a quake theme--as only slightly to moderately intense, in contrast to some clinical assumptions that exposure to a traumatic event sparks particularly vivid nightmares, report psychologist James M. Wood of the University of Arizona in Tucson and his colleagues.

The findings, described in the May JOURNAL OF ABNORMAL PSYCHOLOGY, come from the first controlled study of nightmares following a natural disaster. No data exist regarding nightmares following rape, other crimes or accidents, Wood adds. Several studies report frequent nightmares among combat veterans, based on their recall of nightmares experienced over the past several weeks or months, an approach that tends to underestimate nightmare frequency, Wood argues.

Wood's group had students fill out dream logs each morning for three weeks, beginning one to two weeks after the earthquake. The final sample consisted of 35 San Jose State University students, 56 Stanford University students and 97 University of Arizona students, who acted as controls. Both groups of California students rated their situation during the earthquake as slightly to moderately dangerous and cited moderate anxiety when the earthquake occurred.

During the study, three-quarters of the San Jose State students and two-thirds of the Standford students reported at least one nightmare, compared with one-half of the Arizona students. The researchers defined nightmares as "frightening dreams with visual content and an elaborated story." California students reported an average of nearly three nightmares, Arizona students about half that number.

About 40 percent of the Bay area students reported one or more nightmares about an earthquake, compared with 5 percent of those in Arizona. However, ratings of nightmare intensity on a five-point scale did not differ across the three sites. California students' earthquake nightmares were no more emotionally intense than other frightening dreams.

Earthquake nightmares rarely replayed the actual earthquake experience, Wood says. One woman dreamed that another earthquake opened a trench in the road that then came into her house. She rated the dream as "not intense."

The findings suggest that the normal dreaming process incorporates recent stressful and threatening events into an increased number of nightmares of surprisingly modest emotional intensity, Wood asserts. Researchers do not know whether California students eventually returned to pre-quake nightmare levels or if some will have nightmares about the disaster for years to come, a phenomenon observed among Vietnam combat veterans and children rescued from kidnappers.

The paucity of nightmare research in the population at large makes any generalization from the current study speculative, Wood acknowledges. For instance, his team cannot rule out the possibility that California residents generally have more nightmares about earthquakes than do Arizona residents.

In a previous study, Wood and Arizona psychologist Richard R. Bootzin found that both anxious and calm college students report an annual average of 24 nightmares, about twice the number previously assumed (SN: 3/3/90, p.132). Another study recently completed by Wood and psychologist Marie-Anne Salvio of the Veterans Administration Medical Center in Palo Alto, Calif., yielded an annual average of 16 nightmares among 50 adults between 60 and 70 years old.

For now, Wood assumes a traumatic experience, a perception of continuing threat or both can lead to a persistently high rate of nightmares. Investigators should also examine whether the nightmares of people suffering from post-traumatic stress disorder typically prove as intense as clinicians often suppose, Wood adds.