SOME COMMENTS ON THE MEASUREMENT OF CIRCADIAN-RHYTHMS AFTER TIME-ZONETRANSITIONS AND DURING NIGHT WORK

Adjustment of circadian rhythms to changed sleep/wake schedules, as af ter time-zone transitions and during night work, is not immediate. Dif ferent variables appear to adjust at different rates, and such externa l and internal dissociation is linked with a general malaise (''jet la g'') after a time-zone transition. Work using ''constant routines'' an d ''purification'' methods indicates that the internal dissociation re sults from differences between variables in the relative contribution of exogenous (''masking'') effects to the measured rhythm. These resul ts indicate, therefore, there is no need to postulate the presence of more than one body clock which is responsible for the endogenous compo nent of a circadian rhythm, and that heavily masked circadian rhythms will be poor indicators of the rate of adjustment of this clock. Never theless, it will be the measured rhythm that describes most directly t he disruption to circadian rhythmicity caused by changed sleep/wake sc hedules.