Circadian rhythms in human performance and mood under constant conditions

Abstract

SUMMARYThis study explored the relationship between circadian performance rhythms and rhythms in rectal temperature, plasma cortisol, plasma melatonin, subjective alertness and well-being. Seventeen healthy young adults were studied under 36 h of 'unmasking' conditions (constant wakeful bedrest, temporal isolation, homogenized 'meals') during which rectal temperatures were measured every minute, and plasma cortisol and plasma melatonin measured every 20 min. Hourly subjective ratings of global vigour (alertness) and affect (well-being) were obtained followed by one of two performance batteries. On odd-numbered hours performance (speed and accuracy) of serial search, verbal reasoning and manual dexterity tasks was assessed. On even-numbered hours, performance (% hits, response speed) was measured at a 25-30 min visual vigilance task. Performance of all tasks (except search accuracy) showed a significant time of day variation usually with a nocturnal trough close to the trough in rectal temperature. Performance rhythms appeared not to reliably differ with working memory load. Within subjects, predominantly positive correlations emerged between good performance and higher temperatures and better subjective alertness; predominantly negative correlations between good performance and higher plasma levels of cortisol and melatonin. Temperature and cortisol rhythms correlated with slightly more performance measures (5/7) than did melatonin rhythms (4/7). Global vigour correlated about as well with performance (5/7) as did temperature, and considerably better than global affect (1/7). In conclusion: (1) between-task heterogeneity in circadian performance rhythms appeared to be absent when the sleep/wake cycle was suspended; (2) temperature (positively), cortisol and melatonin (negatively) appeared equally good as circadian correlates of performance, and (3) subjective alertness correlated with performance rhythms as well as (but not better than) body temperature, suggesting that performance rhythms were not directly mediated by rhythms in subjective alertness.

A Parallelism between Human Body Temperature and Performance Independent of the Endogenous Circadian Pacemaker

“…With regard to ECP influence, the present results confirm earlier studies (e.g., Johnson et al, 1992;Dijk et al, 1992;Monk et al, 1997) that have concluded that troughs in performance and temperature occur together when educed at a period length of tau or when studied in a protocol involving a suspension of the sleep/wake cycle. Indeed, they extend the generality of previous findings to a broader range of tasks than that previously studied under forced desynchrony.…”

“…Thus, the phase of the ECP at which body temperature was lowest corresponded exactly to the phase at which performance was lowest, whatever the task given. This has very recently been confirmed using unmasking studies of dexterity, serial search, and verbal reasoning performance in our own laboratories (Monk et al, 1997). Noted in Johnson et al's (1992) and Dijk et al's (1992) studies, but comparatively underemphasized, was the fact that when educed at T, both temperature and performance still showed rhythms (or, more accurately, time of day effects given that performance was not assessed during sleep).…”

“…Whereas Kleitman (1963) espoused a causal relationship, Colquhoun and coworkers (in today's terms) considered performance and body temperature rhythms to be "sister" rhythms, both driven by the endogenous circadian pacemaker (ECP). In a series of studies (summarized in Folkard and Monk, 1985;Folkard, 1983Folkard, , 1989Monk, 1986), the Colquhoun group demonstrated that there were intertask differences not only in baseline time of day effects but also in the rate of phase adjustment to a phase shift (Hughes and Fol-kard, 1976;Monk et al, 1978). This suggested that rhythmic processes other than the ECP were additionally involved in determining how performance might change over the 24 h. The obvious candidate was time since waking (a variable related to Process S, the Y oscillator or Group II oscillators, the term used depending on the model employed).…”

The Effects of Total Sleep Deprivation on Cerebral Responses to Cognitive Performance

“…Our study measured cerebral responses in the early evening when participants were near, if not in, the Wake Maintenance Zone (WMZ). The WMZ is a time of day when the drive of the circadian system is such that sleep is least likely to occur (Strogatz et al 1987) and cognitive performance is often near its peak (Monk et al 1997). Thus, it may also be the time of day when cerebral adaptation is most likely to be evident.…”

Enhanced mental performance at higher 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.…”