September 19, 2006, Volume 53, No. 4
Back to School: Delayed Sleep Phase Syndrome
When fall comes and it’s time for teens to return to school, they may experience trouble falling asleep at night and getting up in the morning. According to Dr. Grace Pien, with Penn’s Division of Sleep Medicine, these teens may suffer from a sleep disorder called Delayed Sleep Phase Syndrome (DSPS)—when your body’s circadian rhythm makes you want to go to bed much later than what’s considered to be a normal bedtime.
“It happens in adolescents and young adults. When a patient comes in, they think they’re suffering from insomnia, saying they go to bed around 11 p.m. but have trouble falling asleep until hours later. If you dig deeper with them, they’ll tell you that on the nights they stay up late, they have no difficulty falling asleep and once they do go to sleep, they stay asleep until late morning or early afternoon,” Dr. Pien explains.
Dr. Pien explains that the delayed sleep phase syndrome is treatable. For most people, once an external schedule is imposed upon them for work or school where they have to get up early, they are able to adjust their sleep habits, go to bed earlier, and meet their obligations. But for others, there is a real difficulty in adjusting to an earlier sleep schedule and they should see a sleep physician for behavior modification or bright light treatment.
Dr. Pien has this advice for the parents of teenagers, who have been used to staying up late during the summer: Have your teen stick closely to a strict “sleep and wake schedule.” Align that schedule with where you want it to be (for example—to bed at 10 p.m. and up by 7 a.m.). High school students still need 8-9 hours of sleep a night to function well the next day. Be aware, sneaking in just one or two late nights can make the body’s circadian rhythm slide right back into the old delayed schedule.
Lack of Sleep Impairs Commercial Drivers’ Performance
Truck drivers who routinely get too little sleep or suffer from sleep apnea show signs of fatigue and impaired performance that can make them a hazard on the road, according to a study by Penn researchers at the School of Medicine. The study results were published in the August 15 issue of the American Journal of Respiratory and Critical Care Medicine.
Penn researchers examined 406 truck drivers, almost all men and on average 45 years old. Dr. Allan Pack, a sleep expert who directs Penn’s Center for Sleep and Respiratory Neurobiology, said the tired truck drivers had impaired performance similar to that of drivers who are legally drunk.
The truck drivers were given wrist motion detection devices to measure how much they slept during a week and then underwent tests for sleep apnea at the sleep center. About 28% of the drivers were found to have some degree of sleep apnea, with nearly 5% of them having a severe case.
The truck drivers were also given tests to measure daytime sleepiness and performance. Drivers who logged less than five hours of sleep dozed-off more quickly than those who got seven to eight hours of sleep. Drivers with severe sleep apnea also dozed-off more rapidly. A lab test to analyze attention and reaction time and another to gauge “lane tracking ability” also turned up performance impairment among the sleep-deprived.
When the results were compiled, investigators discovered: Just over 5% of drivers showed impairment on all three performance-related tests. Nearly 60% did not fare well by at least one measure. About half of the drivers who got less than five hours of sleep had two or three impairments. That’s compared to 10% of drivers who got more than eight hours of sleep regularly. Likewise, about 60% of the drivers with severe sleep apnea had two or three impairments.
Insights into How Working Memory Works
Memory tests performed with amnesiacs have enabled researchers to refute a long-held belief in an essential difference between long-and short-term memories. In the study, researchers from Penn determined that the hippocampus—a seahorse shaped structure in the middle of the brain—was just as important for retrieving certain types of short-term memories as it is for long-term memories. Their findings were published in the Journal of Neuroscience.
According to Dr. Ingrid Olson, research associate in the department of psychology and researcher at Penn’s Center for Cognitive Neuroscience, the age of the memory—is less important to the hippocampus than is the requirement to form connections between pieces of information to create a coherent episode of memory.
“I can remember what my keys look like, and I can remember where the coffee table is located, but the critical test of my memory is if I can remember that I left my keys on the coffee table,” Dr. Olson said.
To study the role of the hippocampus in forming short-term memories, researchers used visual memory tests to study the ability of nine amnesiacs to recall images presented to them on a screen. These subjects all suffered from damage to their hippocampi and related brain structures, and their lives are ruled by the fact that they can no longer form long-term memories, much like characters from the movies “Memento” or “Finding Nemo.”
The task required amnesiacs and controls to remember three objects, locations or objects in locations over delays of one or eight seconds. The results show that working memory for objects or locations alone was at normal levels, but that memory for object-location conjunctions was severely impaired at eight-second delays.
Socioeconomic Factors: Determinants of Sunburn
According to a study that appears in the Journal of the American Academy of Dermatology, 39% of respondents of a national survey conducted in 2003 had at least one sunburn in the previous 12 months, a 22% increase since 1999. Additionally, this age rose dramatically as income and education levels increased and the age of respondents decreased.
Dr. Joel M. Gelfand, assistant professor of dermatology and co-author of the report, “The epidemiology of sunburn in the U.S. population in 2003,” says, “Our research confirms previous findings that younger adults continue to be the group most likely to get sunburned and, as a result, are at an increased risk for developing future skin cancers.” He adds, “The increased number of sunburns among people with the highest incomes could be attributed to their ability to travel to tropical destinations more often than those with a lower income.”
Dr. Gelfand studied the prevalence of and risk factors for sunburn in the U.S. using a random sample of 207,776 adults. The study revealed that sunburn prevalence was greatest in respondents 18 to 24 years old, with 61% reporting at least one sunburn in the past year. When income and educational levels were examined, individuals in the highest income strata (equal to or greater than $50,000) were more likely to report sunburn than those in the lowest income strata (less than $20,000)—47% vs. 28%, respectively. In addition, respondents with a college degree reported a higher sunburn incidence than those without a high school degree—43% vs. 25%, respectively.
Other variables that had a high correlation to increased sunburns included gender, employment status and alcohol use. Overall, 44% of male respondents reported at least one sunburn compared with 34% of female respondents. Students were nearly twice as likely to sunburn than those who were unemployed (63% vs. 33%, respectively). In addition, 47% of employed respondents reported being sunburned. The study also found that respondents who reported binge drinking—defined as consuming more than 5 drinks in one night within the past 30 days—had a higher prevalence of sunburn than their counterparts (56% vs. 35%, respectively).
Fossils Depict Aquatic Origins for Near-Modern Birds
Five fossil specimens of a near-modern bird found in the Gansu Province of northwestern China show that early birds likely evolved in an aquatic environment, according to a study in the journal Science. Their findings suggest that these early modern birds were much like the ducks or loons found today. Gansus yumenensis, which lived some 105 to 115 million years ago during the Early Cretaceous period, took modern birds through a watery path out of the dinosaur lineage.
The report was co-authored by Dr. Peter Dodson, professor of anatomy in the School of Veterinary Medicine and professor of geology, and his former students Hai-lu You of the Chinese Academy of Geological Sciences, Jerald Harris of Dixie State College of Utah and Matthew Lamanna of Carnegie Natural History Museum in Pittsburgh.
Gansus yumenensis takes its name from the Gansu region, where it was found, and the nearby city of Yumen. According to Dr. Dodson, Gansus is something of a lost species, originally described from a fossil leg found in 1983, but since largely ignored by science. The five specimens described by Dr. Dodson and his colleagues had many of the anatomical traits of modern birds, including feathers, bone structure and webbed feet, although every specimen lacked a skull.
The skeletons, headless as they are, offer plenty of evidence for a life on the water. Its upper body structure offers evidence that Gansus could take flight from the water, like a modern duck, and the webbed feet and bony knees are clear signs that Gansus swam.
“The enantiornitheans had the best adaptations for perching, so they were able to dominate the ecological niche that we would associate with songbirds, cuckoos, woodpeckers or birds of prey,” said Jerald Harris, director of paleontology at Dixie State College of Utah. “Gansus appears to have had adaptations for a lifestyle centered around water, based on things like the proportions of the leg and foot bones.”
While the enantiornitheans are now long gone, their perching lifestyle has now been taken over by the descendents of birds like Gansus. What remains a mystery for now, according to the researchers, is how the amphibious lifestyle of birds like Gansus helped enable them to survive the cataclysmic end of the dinosaurs 65 million years ago.