Inducing jet lag in the laboratory: patterns of adjustment to an acute shift in routine

Eight middle-aged males were studied in a temporal isolation experimental lasting 15 d. After 5 d and nights of entrainment to his own habitual routine, each subject experienced an acute, unheralded 6-h phase advance in routine, accomplished by truncating his sixth sleep episode. For the remaining 10 d of the study, subjects were held to a routine 6-h phase advanced to the original. Significant symptoms of jet lag appeared in mood, performance efficiency, sleep, and circadian temperature rhythms. When plotted as a function to "days post-shift," some variables (temperature phase, percent rapid eye movement sleep) showed a fairly monotonic recovery to baseline levels. However, other variables (actual sleep duration, percent slow wave sleep, motivation loss, subjective sleepiness) showed a zig-zag recovery pattern, suggesting the interaction of two competing processes, and reinforcing the need for greater sophistication in the development of jet lag coping strategies.