Here in this space, I would like to collect materials and resources I find useful or illuminating with regards to studying and understanding of sleep, dreams, and hypnagogic states.
Natural sleep and its seasonal variations in three pre-industrial societies
How did humans sleep before the modern era? Because the tools to measure sleep under natural conditions were developed long after the invention of the electric devices suspected of delaying and reducing sleep, we investigated sleep in three preindustrial societies[1–3]. We find that all three show similar sleep organization, suggesting that they express core human sleep patterns, likely characteristic of pre-modern era Homo sapiens. Sleep periods, the times from onset to offset, averaged 6.9–8.5-h, with sleep durations of 5.7–7.1-h, amounts near the low end of those industrial societies[4–7]. There was a difference of nearly 1-h between summer and winter sleep. Daily variation in sleep duration was strongly linked to time of onset, rather than offset. None of these groups began sleep near sunset, onset occurring, on average, 3.3-h after sunset. Awakening was usually before sunrise. The sleep period consistently occurred during the nighttime period of falling environmental temperature, was not interrupted by extended periods of waking and terminated, with vasoconstriction, near the nadir of daily ambient temperature. The daily cycle of temperature change, largely eliminated from modern sleep environments, may be a potent natural regulator of sleep. Light exposure, was maximal in the morning greatly decreasing at noon, indicating that all three groups seek shade at midday and that light activation of the suprachiasmatic nucleus is maximal in the morning. Napping occurred on <7% of days in winter and <22% of days in summer. Mimicking aspects of the natural environment might be effective in treating certain modern sleep disorders.
Effects of Lights of Different Color Temperature on the Nocturnal Changes in Core Temperature and Melatonin in Humans
[Applied Human Science]
A variety of types of artificial illumination has recently become available, differing in the quality of illumination and range of color temperature. In our previous studies we found that in subjects with normal color vision the nocturnal fall in core temperature and the increase of urinary melatonin excretion were suppressed by bright blue or green light, but not by bright red or dim lights. The aim of our present study was to examine from the view point of chronobiology whether the lights of different color temperature often used in everyday life may affect core temperature and urinary melatonin secretion differently. Experiments were carried out on five subjects with normal color vision. They were exposed for 5 hr (from 21:00 h to 2:00 h) to two kinds of bright (1000 lx) light of different color temperature (6500 K, 3000K) with dim (50 lx) light as a control; after exposure they slept in darkness. Our main results were as follows: The light with a high color temperature of 6500 K more strongly suppressed the nocturnal fall of the core temperature and the nocturnal increase of melatonin secretion than the light with a low color temperature of 3000 K. This difference was particularly evident for core temperature during the sleep period following experimental illumination.
Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed
[J Clin Sleep Med]
STUDY OBJECTIVE: Sleep hygiene recommendations are widely disseminated despite the fact that few systematic studies have investigated the empirical bases of sleep hygiene in the home environment. For example, studies have yet to investigate the relative effects of a given dose of caffeine administered at different times of day on subsequent sleep.
METHODS: This study compared the potential sleep disruptive effects of a fixed dose of caffeine (400 mg) administered at 0, 3, and 6 hours prior to habitual bedtime relative to a placebo on self-reported sleep in the home. Sleep disturbance was also monitored objectively using a validated portable sleep monitor.
RESULTS: Results demonstrated a moderate dose of caffeine at bedtime, 3 hours prior to bedtime, or 6 hours prior to bedtime each have significant effects on sleep disturbance relative to placebo (p < 0.05 for all).
CONCLUSION: The magnitude of reduction in total sleep time suggests that caffeine taken 6 hours before bedtime has important disruptive effects on sleep and provides empirical support for sleep hygiene recommendations to refrain from substantial caffeine use for a minimum of 6 hours prior to bedtime.
Night Watch in One Brain Hemisphere during Sleep Associated with the First-Night Effect in Humans
We often experience troubled sleep in a novel environment . This is called the first-night effect (FNE) in human sleep research and has been regarded as a typical sleep disturbance [2, 3, 4]. Here, we show that the FNE is a manifestation of one hemisphere being more vigilant than the other as a night watch to monitor unfamiliar surroundings during sleep [5, 6]. Using advanced neuroimaging techniques [7, 8] as well as polysomnography, we found that the temporary sleep disturbance in the first sleep experimental session involves regional interhemispheric asymmetry of sleep depth . The interhemispheric asymmetry of sleep depth associated with the FNE was found in the default-mode network (DMN) involved with spontaneous internal thoughts during wakeful rest [10, 11]. The degree of asymmetry was significantly correlated with the sleep-onset latency, which reflects the degree of difficulty of falling asleep and is a critical measure for the FNE. Furthermore, the hemisphere with reduced sleep depth showed enhanced evoked brain response to deviant external stimuli. Deviant external stimuli detected by the less-sleeping hemisphere caused more arousals and faster behavioral responses than those detected by the other hemisphere. None of these asymmetries were evident during subsequent sleep sessions. These lines of evidence are in accord with the hypothesis that troubled sleep in an unfamiliar environment is an act for survival over an unfamiliar and potentially dangerous environment by keeping one hemisphere partially more vigilant than the other hemisphere as a night watch, which wakes the sleeper up when unfamiliar external signals are detected.
Pre-sleep treatment with galantamine stimulates lucid dreaming: A double-blind, placebo-controlled, crossover study
Lucid dreaming is a remarkable state of consciousness in which one is aware of the fact that one is dreaming while continuing to dream. Based on the strong relationship between physiological activation during rapid eye-movement sleep and lucid dreaming, our pilot research investigated whether enhancing cortical activation via acetylcholinesterease inhibition (AChEI) would increase the frequency of lucid dreams and found AChEI to be a promising method for lucid dream induction. In the current study we sought to quantify the size and reliability of the effect of AChEI on lucid dreaming, dream recall and dream content as well as to test the effectiveness of an integrated lucid dream induction protocol which combined cholinergic stimulation with other methods for lucid dream induction. Participants (N = 121) with high dream recall and an interest in lucid dreaming were randomly assigned counterbalanced orders of 3 doses of galantamine (0, 4 and 8 mg). On 3 consecutive nights, they awoke approximately 4.5 hours after lights out, recalled a dream, ingested the capsules and stayed out of bed for at least 30 minutes. Participants then returned to bed and practiced the Mnemonic Induction of Lucid Dreams technique while returning to sleep. The percentage of participants who reported a lucid dream was significantly increased for both 4 mg (27%, odds ratio = 2.29) and 8 mg doses (42%, odds ratio = 4.46) compared to the active placebo procedure (14%). Galantamine also significantly increased dream recall, sensory vividness and complexity (p<0.05). Dream recall, cognitive clarity, control, positive emotion, vividness and self-reflection were increased during lucid compared to non-lucid dreams (p<0.0001). These results show that galantamine increases the frequency of lucid dreams in a dose-related manner. Furthermore, the integrated method of taking galantamine in the last third of the night with at least 30 minutes of sleep interruption and with an appropriately focused mental set is one of the most effective methods for inducing lucid dreams available today.
Fatigue is a Brain-Derived Emotion that Regulates the Exercise Behavior to Ensure the Protection of Whole Body Homeostasis
An influential book written by A. Mosso in the late nineteenth century proposed that fatigue that "at first sight might appear an imperfection of our body, is on the contrary one of its most marvelous perfections. The fatigue increasing more rapidly than the amount of work done saves us from the injury which lesser sensibility would involve for the organism" so that "muscular fatigue also is at bottom an exhaustion of the nervous system." It has taken more than a century to confirm Mosso's idea that both the brain and the muscles alter their function during exercise and that fatigue is predominantly an emotion, part of a complex regulation, the goal of which is to protect the body from harm. Mosso's ideas were supplanted in the English literature by those of A. V. Hill who believed that fatigue was the result of biochemical changes in the exercising limb muscles - "peripheral fatigue" - to which the central nervous system makes no contribution. The past decade has witnessed the growing realization that this brainless model cannot explain exercise performance. This article traces the evolution of our modern understanding of how the CNS regulates exercise specifically to insure that each exercise bout terminates whilst homeostasis is retained in all bodily systems. The brain uses the symptoms of fatigue as key regulators to insure that the exercise is completed before harm develops. These sensations of fatigue are unique to each individual and are illusionary since their generation is largely independent of the real biological state of the athlete at the time they develop. The model predicts that attempts to understand fatigue and to explain superior human athletic performance purely on the basis of the body's known physiological and metabolic responses to exercise must fail since subconscious and conscious mental decisions made by winners and losers, in both training and competition, are the ultimate determinants of both fatigue and athletic performance.
Findings From the International Lucid Dream Induction Study
The International Lucid Dream Induction Study (ILDIS) investigated and compared the effectiveness of five different combinations of lucid dream induction techniques including reality testing (RT), Wake Back to Bed (WBTB), the Mnemonic Induction of Lucid Dreams (MILD) technique, the Senses Initiated Lucid Dream (SSILD) technique, and a hybrid technique combining elements of both MILD and SSILD. Participants with an interest in lucid dreaming (N = 355) completed a pre-test questionnaire and then a baseline sleep and dream recall logbook for one week before practicing the lucid dream induction techniques for another week. Results indicated that the MILD technique and the SSILD technique were similarly effective for inducing lucid dreams. The hybrid technique showed no advantage over MILD or SSILD. Predictors of successful lucid dream induction included superior general dream recall and the ability to fall asleep within ten minutes of completing the lucid dream induction techniques. Successful lucid dream induction had no adverse effect on sleep quality. Findings indicated that the techniques were effective regardless of baseline lucid dreaming frequency or prior experience with lucid dreaming techniques. Recommendations for further research on lucid dream induction techniques are provided.