Completed Studies

An Examination of Circasemidian Rhythms in Human
Body Temperature, Sleepiness and Response Time


There are a number of data sets in the literature that show a daily two-peak error pattern. However, there is controversy over the existence of physiological or behavioral circasemidian rhythms. Apparently, no evidence exists to support the presence of a circasemidian rhythm in the rhythmic cells of the suprachiasmatic nucleus, the accepted timing source for the major circadian rhythms of the body. On the other hand, it is extremely common for any oscillator to be affected by external factors that set up harmonic frequencies in its expression. This may be the case in the expression of the fundamental human circadian rhythm (24-hour cycle length) and its first harmonic (12-hour cycle length) at physiological, behavioral and levels.


The goal of this research is to measure human physiological, subjective and behavioral rhythms under relatively constant environmental conditions.


A group of 68 volunteers participated in this effort. The group consisted of both males and females between the ages of 18 and 62. On the test day, half-hourly testing occurred in a fixed order: response time test (on a PC), sleepiness rating (one written number), and temperature measurement (using the infra-red ear device that is available in drug stores). Half-hourly measurements were acquired from 0700 through 19:00. Participants remained in a closed, controlled-access bedroom at the Fatigue Countermeasures Lab and were fed on a quasi-random schedule.