EDITORIAL FOCUS
Enhanced mental performance at higher body temperature?

¹ Endocrinology, Department of Medicine (MC1027), University of Chicago, Chicago, Illinois 60637; and ² Johannes-Müller-Institut für Physiologie, Humboldt-Universität (Charité), D-10117 Berlin, Germany

	ARTICLE

TOP ARTICLE REFERENCES

MOST OF US HAVE HAD THE REMARKABLE experience of performing several mental tasks very well during slight fever or while body temperature rises unexpectedly during jet lag. This may not simply be a misperception related to the fever process or desynchrony, as pointed out by Wright and colleagues (13) in this issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.

Most neurobehavioral measures depend essentially on two processes: a circadian process depending on the time of day and a homeostatic process relating sleep duration and intensity to the amount of prior wakefulness (2, 7). Body temperature levels also demonstrate a circadian pattern (4, 6, 11), with high levels during the day and low levels during the night. Sleep exerts an influence on body temperature levels because under conditions of total sleep deprivation, the circadian rhythm of body temperature is preserved, but its amplitude is reduced to 0.5°C, compared with an amplitude of ~1°C when sleep occurs at a normal time (12).

The relationship between the circadian rhythms of body temperature and performance in simple repetitive tasks was already shown by Kleitman in 1963 (9) and by Colquhoun in 1971 (3). Performance for this type of task parallels the circadian rhythm of body temperature. More recent studies have shown a similar relationship when data were collected during extended wakefulness. Minimum performance coincides with low levels of body temperature (1, 5, 8, 10). In these studies, the pressure of the homeostatic process, because of sleep deprivation, continues to increase. Therefore, to distinguish the effects of the homeostatic process from those of the circadian process, some groups have used the forced desynchrony protocol. Under conditions in which the volunteers, for instance, live on 28-h days (with 9 h and 20 min allocated for sleep), the internal clock is not able to synchronize to the environment, allowing for the examination of variables at different circadian phases without sleep depriving the subjects. The parallelism between the circadian rhythms of body temperature and performance on various tasks persists and alertness deteriorates with time spent awake (5, 8). Similar findings have been found when subjects lived on a 20-h day (14).

In this issue, Wright et al. (13) report a study in which the subjects performed various tasks during the forced desynchrony protocol, allowing a few observations of the relationship between body temperature and performance at the same circadian phases and after the same amount of hours spent awake. They then split the performance results between the corresponding lowest or highest body temperature for each subject at various circadian phases and at various hours being awake. Globally, better performance is associated with higher body temperature levels, independently of circadian phase and time spent awake. The authors conclude that body temperature is a modulator of the neurobehavioral function.

Kleitman and Jackson hypothesized in 1950 that changes in alertness could be derived from variations in body temperature avoiding "time consuming performance tests which, in themselves, interfere with, or disrupt, the scheduled activities of the persons studied" (see Ref. 2). The complex analysis by Wright et al. verifies this assumption.

	FOOTNOTES

10.1152/ajpregu.00524.2002

	REFERENCES

TOP ARTICLE REFERENCES

1.   Babkoff, H, Mikulincer M, Caspy T, Kempinski D, and Sing H. The topology of performance curves during 72 hours of sleep loss: a memory and search task. Q J Exp Psychol B 40: 737-756, 1988.

2.   Carrier, J, and Monk T. Circadian rhythms of performance: new trends. Chronobiol Int 17: 719-732, 2000[Web of Science][Medline].

3.   Colquhoun, WP. Biological Rhythms and Human Performance. London: Academic, 1971.

4.   Danel, T, Libersa C, and Touitou Y. The effect of alcohol consumption on the circadian control of human core body temperature is time dependent. Am J Physiol Regul Integr Comp Physiol 281: R52-R55, 2001[Abstract/Free Full Text].

5.   Dijk, DJ, Duffy JF, and Czeisler CA. Circadian and sleep/wake dependent aspects of subjective alertness and cognitive performance. J Sleep Res 1: 112-117, 1992[Medline].

6.   Dijk, DJ, Neri DF, Wyatt JK, Ronda JM, Riel E, Ritz-De Cecco A, Hughes RJ, Elliott AR, Prisk GK, West JB, and Czeisler CA. Sleep, performance, circadian rhythms, and light-dark cycles during two space shuttle flights. Am J Physiol Regul Integr Comp Physiol 281: R1647-R1664, 2001[Abstract/Free Full Text].

7.   Folkard, S, and Akerstedt T. A three-process model of the regulation of alertness-sleepiness. In: Sleep, Arousal and Performance: A Tribute to Bob Wilkinson, edited by Broughton RJ, and Ogilvie RD.. Boston: Birkhauser, 1992, p. 11-26.

8.   Johnson, MP, Duffy JF, Dijk DJ, Ronda JM, Dyal CM, and Czeisler CA. Short-term memory, alertness and performance: a reappraisal of their relationship to body temperature. J Sleep Res 1: 24-29, 1992[Medline].

9.   Kleitman, N. Sleep and Wakefulness. Chicago: University of Chicago Press, 1963.

10.   Monk, TH, Buysse DJ, Reynolds CF, III, Berga SL, Jarret DB, Begley AE, and Kupfer DJ. Circadian rhythms in human performance and mood under constant conditions. J Sleep Res 6: 9-18, 1997[Web of Science][Medline].

11.   Sharkey, KM, and Eastman CI. Melatonin phase shifts human circadian rhythms in a placebo-controlled simulated night-work study. Am J Physiol Regul Integr Comp Physiol 282: R454-R463, 2002[Abstract/Free Full Text].

12.   Van Cauter, E, Sturis J, Byrne MM, Blackman JD, Leproult R, Ofek G, L'Hermite-Balériaux M, Refetoff S, Turek F, and Van Reeth O. Demonstration of rapid light-induced advances and delays of the human circadian clock using hormonal phase markers. Am J Physiol 266: E953-E963, 1994[Abstract/Free Full Text].

13.   Wright, KP, Jr, Hull JT, and Czeisler CA. Relationship between alertness, performance and body temperature in humans. Am J Physiol Regul Integr Comp Physiol 283: R1370-R1377, 2002[Abstract/Free Full Text].

14.   Wyatt, JK, Ritz-De Cecco A, Czeisler CA, and Dijk DJ. Circadian temperature and melatonin rhythms, sleep, and neurobehavioral function in humans living on a 20-h day. Am J Physiol Regul Integr Comp Physiol 277: R1152-R1163, 1999[Abstract/Free Full Text].