Impact of age, sleep pressure and circadian phase on time-of-day estimates

The effect of 24-hour sleep deprivation on subjective time perception

In this study, we investigated the effect of 24-h total sleep deprivation on subjective time perception. Twenty-five participants aged 18-35 years (13 female and 12 male) were recruited. Time perception and cognitive assessments were performed twice: after a regular night's sleep and following a 24-h sleep deprivation. The retrospective and prospective tasks were used to measure time perception. In order to prevent order effect, the test orders were randomized. The Stroop test and the Wechsler Memory Scale-III were used to evaluate attention, processing speed, and memory. The repeated measures ANOVA was used to examine gender-by-sleep deprivation interactions on time perception. We found that retrospective time perception was significantly prolonged after sleep deprivation (p < 0.05). Women had a shorter prospective time estimation rate after adequate sleep than men, but this difference disappeared after sleep deprivation. The Stroop test showed improvement in cognitive flexibility after sleep deprivation (p < 0.05), and short-term or working memory appeared unaffected by one night of sleep deprivation. There was a negative correlation between sleepiness rate and working memory function in female subgroup. The results suggest that even short-term sleep deprivation can significantly affect time perception, which may have important implications in critical situations.

Circadian rhythmicity of body temperature and metabolism

This article reviews the literature on the circadian rhythms of body temperature and whole-organism metabolism. The two rhythms are first described separately, each description preceded by a review of research methods. Both rhythms are generated endogenously but can be affected by exogenous factors. The relationship between the two rhythms is discussed next. In endothermic animals, modulation of metabolic activity can affect body temperature, but the rhythm of body temperature is not a mere side effect of the rhythm of metabolic thermogenesis associated with general activity. The circadian system modulates metabolic heat production to generate the body temperature rhythm, which challenges homeothermy but does not abolish it. Individual cells do not regulate their own temperature, but the relationship between circadian rhythms and metabolism at the cellular level is also discussed. Metabolism is both an output of and an input to the circadian clock, meaning that circadian rhythmicity and metabolism are intertwined in the cell.

Modeling circadian and sleep-homeostatic effects on short-term interval timing

Short-term interval timing i.e., perception and action relating to durations in the seconds range, has been suggested to display time-of-day as well as wake dependent fluctuations due to circadian and sleep-homeostatic changes to the rate at which an underlying pacemaker emits pulses; pertinent human data being relatively sparse and lacking in consistency however, the phenomenon remains elusive and its mechanism poorly understood. To better characterize the putative circadian and sleep-homeostatic effects on interval timing and to assess the ability of a pacemaker-based mechanism to account for the data, we measured timing performance in eighteen young healthy male subjects across two epochs of sustained wakefulness of 38.67 h each, conducted prior to (under entrained conditions) and following (under free-running conditions) a 28 h sleep-wake schedule, using the methods of duration estimation and duration production on target intervals of 10 and 40 s. Our findings of opposing oscillatory time courses across both epochs of sustained wakefulness that combine with increasing and, respectively, decreasing, saturating exponential change for the tasks of estimation and production are consistent with the hypothesis that a pacemaker emitting pulses at a rate controlled by the circadian oscillator and increasing with time awake determines human short-term interval timing; the duration-specificity of this pattern is interpreted as reflecting challenges to maintaining stable attention to the task that progressively increase with stimulus magnitude and thereby moderate the effects of pacemaker-rate changes on overt behavior.

The influence of test experience and NK1 receptor antagonists on the performance of NK1R-/- and wild type mice in the 5-Choice Serial Reaction-Time Task

Genetically-altered mice, lacking functional NK1 receptors (NK1R-/-), express abnormal behaviours that are prominent in Attention Deficit Hyperactivity Disorder: namely, inattentiveness and impulsivity (indicated by their greater % omissions and premature responses in the 5-Choice Serial Reaction-Time Task (5-CSRTT) and locomotor hyperactivity. We investigated how behaviour in the 5-CSRTT is affected by repeated testing and whether the abnormalities expressed by NK1R-/- mice are mimicked by treating wild type mice with a NK1R antagonist (L 733060 or RP 67580; 5 or 10 mg/kg). Repeated testing with a variable (VITI) or fixed, prolonged (LITI) intertrial interval reduced % omissions. Premature responses also declined, but only in NK1R-/- mice, in the VITI test. By contrast, perseveration increased in both genotypes. RP 67580 (10 mg/kg) increased the % omissions in both genotypes in the VITI, an action which cannot be attributed to NK1R antagonism. Neither drug affected perseveration. However, for premature responses, the response profile suggested that the low and high doses of RP 67580 (VITI) and L 733060 (LITI) had opposing effects on this behaviour. We infer that the effect of NK1R antagonists in the 5-CSRTT is confounded by animals' test experience and non-specific drug effects at sites other than NK1R, possibly L-type Ca²⁺(v) channels.

Functional CLOCK gene rs1554483 G/C polymorphism is associated with susceptibility to Alzheimer's disease in the Chinese population

OBJECTIVE

To examine the association between the circadian locomotor output cycles kaput (CLOCK) gene rs1554483 G/C polymorphism and susceptibility to Alzheimer's disease in Chinese people.

METHODS

This case-control study determined apolipoprotein E (APOE) and CLOCK rs1554483 G/C genotypes using polymerase chain reaction restriction fragment length polymorphism.

RESULTS

Unrelated patients with Alzheimer's disease (n = 130) and healthy controls (n = 188) were analysed for an association between the CLOCK gene rs1554483 G/C polymorphism and susceptibility to Alzheimer's disease. In the whole sample and in APOE ε4 isoform noncarriers, the prevalence of CLOCK gene rs1554483 G allele carriers was significantly higher in patients with Alzheimer's disease than in controls. Among APOE ε4 carriers, the prevalence of CLOCK rs1554483 G allele carriers was not significantly different between patients with Alzheimer's disease and controls.

CONCLUSION

Among APOE ε4 noncarriers, but not APOE ε4 carriers, the CLOCK rs1554483 G allele was associated with increased susceptibility to Alzheimer's disease.

Increased cerebral blood flow in the right frontal lobe area during sleep precedes self-awakening in humans

BACKGROUND

Some people can subconsciously wake up naturally (self-awakening) at a desired/planned time without external time stimuli. However, the underlying mechanism regulating this ability remains to be elucidated. This study sought to examine the relationship between hemodynamic changes in oxyhemoglobin (oxy-Hb) level in the prefrontal cortex and sleep structures during sleep in subjects instructed to self-awaken.

RESULTS

Fifteen healthy right-handed male volunteers with regular sleep habits participated in a consecutive two-night crossover study. The subjects were instructed to wake up at a specified time ("request" condition) or instructed to sleep until the morning but forced to wake up at 03:00 without prior notice ("surprise" condition). Those who awoke within ± 30 min of the planned waking time were defined as those who succeeded in self-awakening ("success" group). Seven subjects succeeded in self-awakening and eight failed.No significant differences were observed in the amounts of sleep in each stage between conditions or between groups. On the "request" night, an increase in oxy-Hb level in the right prefrontal cortex and a decrease in δ power were observed in the "success" group around 30 min before self-awakening, whereas no such changes were observed in the "failure" group. On the "surprise" night, no significant changes were observed in oxy-Hb level or δ power in either group.

CONCLUSIONS

These findings demonstrate a correlation between self-awakening and a pre-awakening increase in hemodynamic activation in the right prefrontal cortex, suggesting the structure's contribution to time estimation ability.

Diurnal fluctuations in subjective sleep time in humans

Humans have the ability to estimate the passage of time in the absence of external time cues. In this study, we subjected 22 healthy males (aged 21.8±1.9 years) to a 40-min nap trial followed by 80min of wakefulness repeated over 28h, and investigated the relationship between various sleep parameters and the discrepancy (ΔST) of time estimation ability (TEA) during sleep, defined by the difference between actual sleep time (ST) and subjective sleep time (sub-ST) in each nap interval. Both ST and sub-ST were significant diurnal fluctuations with the peak in the early morning (9h after dim-light melatonin onset time, 2h after nadir time of core body temperature rhythm), and subjective sleep duration was estimated to be longer than actual times in all nap intervals (sub-ST>ST). There were significant diurnal fluctuations in discrepancy (sub-ST-ST) of TEA during sleep, and the degree of discrepancy correlated positively with increase in the amount of REM sleep and decrease in the amount of slow-wave sleep. These findings suggest that human TEA operates at a certain level of discrepancy during sleep, and that this discrepancy might be related to the biological clock and its associated sleep architecture.