PITTSBURGH, September 15, 1997 — "Burning the midnight oil" may do more harm than good for people who believe they work best at night. In a study at the University of Pittsburgh Medical Center's (UPMC) Western Psychiatric Institute and Clinic, researchers have found that the body's need for sleep, influenced by its circadian rhythms, may slow down thinking processes at night. Also, researchers at the UPMC said, losing sleep at night can slow down your thinking skills the next day.
From a practical point of view, results suggest that in addition to safety concerns resulting from night workers' and night drivers' tendency to fall asleep, it should be recognized that even if they are wide awake, they may be thinking more slowly.
The UPMC study, published by Timothy H. Monk, Ph.D., professor of psychiatry, and Julie Carrier, Ph.D., postdoctoral research fellow, in the current issue of the academic journal Sleep, suggests that circadian rhythms, the body's internal clock, can affect the speed at which the brain processes information. According to Dr. Monk, the study's principal investigator, night-time thinking may slow down because people need to fight their urges to sleep.
Eighteen healthy young adults participated in the 36-hour study that involved constant wakeful bed rest, or being kept awake while in bed, for the duration of the study. Participants also had no knowledge of clock time, and meals were replaced by hourly nutritional supplements. This was done to avoid feelings of sleepiness that accompany big meals. A series of performance tests involving figuring out whether sentences were true or false were given every other hour, and the speed and accuracy of the responses were recorded.
Using questions phrased in both the positive and negative voice, the researchers found that negative-voiced sentences took longer for participants to respond to than positive-voiced ones due to an increase in information-processing requirements. By plotting the speed with which this extra processing was done at each time of day and night, Drs. Monk and Carrier were able to factor out overall effects of sluggishness and inattention and get directly at the speed of thought itself. The study concluded that people think more slowly at night, perhaps because they approach a task differently at night than during the day. It also showed a slowing in the speed of information processing during the day after the lost night of sleep.