Field study for shift of sleep-wake cycle and inter-individual differences

1993 Fiscal Year Final Research Report Summary

• Project/Area Number: 04610083
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: Psychology
• Research Institution: Notre Dame Seishin University
• Principal Investigator: ISHIHARA Kaneyoshi Faculty of Home Economics, Dept.of Child Welfare, Assoc.Prof., 家政学部・児童学科, 助教授 (80159756)
• Project Period (FY): 1992 – 1993
• Keywords: Circadian rhythm / Diurnal type / Sliding shift / Body temperature / Wrist activity / Sleepiness

Research Abstract

The purpose of the present study was to investigate the adaptation process of circadian system under a 25-hr sliding shift condition from the view point of diurnal types (morning type and evening type). The 25-hr sliding shift was the procedure in which the subject's sleep-wake cycle was prolonged to 25-hr in daily life environment.
Fourteen female university students (5 morning and 9 evening type subjects) participated in this experiment that consisted of 4 control days (baseline), 4 sliding shifts and 4 recovery days. Rectal temperature was recorded every 5 min by means of an ambulatory temperature data collector Anritsu Meter Co., TM-5310) and wrist activities in a 5-min epoch were recorded by means of the Motionlogger Actigraph (Ambulatory Monitoring Inc.) placed on the subject's nondominant wrist.
The morning type subjects were compared with the evening type subjects in regard to sleep length, wrist activity, rectal temperature and subjective sleepiness. From the results by cosinor analysis, circadian periods of temperature and sleep-wake rhythms extended more in the evening types than in the morning types, i.e., the period of the evening type was near 25-hours. The peak times during the sliding shift period, however, were almost unchanged for both types. Therefore, it seemed that the body temperature rhythm did no completely adjust to the shift schedule. Sleep length of the morning type was remarkably short during the first half of the shift period, compared with that of the evening type. Contrary to these results, subjective sleepiness was lower in the morning type than in the evening type. We, however, could not conclude that the morning type subjectively adapted better to the shift than the evening type, because the differences of sleepiness between the two types were also observed during the control period. Finally, our results suggested that the evening type more easily, but not completely, adapted than the morning type to the 25-hr sliding shift.