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Can we sleep throughout our whole life if we are supplied the necessary things like food,water etc.
Q: Is there any Sleep limit for a human body? Can we sleep throughout our whole life if we are supplied the necessary things like food,water etc.
A: Yes, there is a sleep limit for human (and other animals that sleep). And, no, we can't sleep throughout our whole life even if all our metabolic requirements are supported. This is because sleep does not occur freely without any control but is under control of a complex neural network. This network limits how long one can sleep or be awake. It also regulates the time when sleep is to begin and to end. (Ref 1 - 4)
Sleep occurs alternately with wake in cycles, called sleep-wake cycle. These cycles are under control of a complex network of neural circuits in the brainstem, hypothalamus, basal ganglia, basal forebrain, and thalamus (see figure below).
(The figure is from Figure 2, Ref 1.)
And the periodicity of the cycles are controlled by circadian rhythm pacemaker in suprachiasmatic nucleus, internal homeostasis, and ambient light. (see figure below)
(This figure is from Figure 3, Ref 1)
In human and animals that sleep, this cycle is about 24 hours, with the mean duration of sleep (in human) of about 7.5 hours (with a standard deviation of about 1.25 hours) (Ref 2.). So, normally we sleep about 7.5 hours and then are set to be awake by these neural mechanisms. Because sleep is under control of these neural circuits, we cannot just fall asleep whenever we want and cannot sleep as many hours as we would like.
Larson-Prior, Linda & Ju, Yo-El & Galvin, James. (2014). Cortical-Subcortical Interactions in Hypersomnia Disorders: Mechanisms Underlying Cognitive and Behavioral Aspects of the Sleep-Wake Cycle. Frontiers in neurology. 5. 165. 10.3389/fneur.2014.00165.
Purves D. Chapter 27 Sleep and Wakefulness. Purves D, Augustine GJ, David Fitzpatrick D, Hall WC, Lamantia AS, McNamara JO, Williams SM, editors. Neuroscience. 3rd ed. Sunderland, Massachusetts: Sinauer Associates Inc; 2004. ISBN-13: 9780878937257 ISBN-10: 0878937250. p659-686.
Moore RY. Clinical Update - Circadian Rhythms, Hypothalamus, and Regulation of the Sleep-Wake Cycle. Medscape. 2019 Sep 1.
Genes do not exist in a vacuum. Although we are all biological organisms, we also exist in an environment that is incredibly important in determining not only when and how our genes express themselves, but also in what combination. Each of us represents a unique interaction between our genetic makeup and our environment range of reaction is one way to describe this interaction. Range of reaction asserts that our genes set the boundaries within which we can operate, and our environment interacts with the genes to determine where in that range we will fall. For example, if an individual’s genetic makeup predisposes her to high levels of intellectual potential and she is reared in a rich, stimulating environment, then she will be more likely to achieve her full potential than if she were raised under conditions of significant deprivation. According to the concept of range of reaction, genes set definite limits on potential, and environment determines how much of that potential is achieved. Some disagree with this theory and argue that genes do not set a limit on a person’s potential.
Another perspective on the interaction between genes and the environment is the concept of genetic environmental correlation . Stated simply, our genes influence our environment, and our environment influences the expression of our genes. Not only do our genes and environment interact, as in range of reaction, but they also influence one another bidirectionally. For example, the child of an NBA player would probably be exposed to basketball from an early age. Such exposure might allow the child to realize his or her full genetic, athletic potential. Thus, the parents’ genes, which the child shares, influence the child’s environment, and that environment, in turn, is well suited to support the child’s genetic potential.
Nature and nurture work together like complex pieces of a human puzzle. The interaction of our environment and genes makes us the individuals we are. (credit “puzzle”: modification of work by Cory Zanker credit “houses”: modification of work by Ben Salter credit “DNA”: modification of work by NHGRI)
In another approach to gene-environment interactions, the field of epigenetics looks beyond the genotype itself and studies how the same genotype can be expressed in different ways. In other words, researchers study how the same genotype can lead to very different phenotypes. As mentioned earlier, gene expression is often influenced by environmental context in ways that are not entirely obvious. For instance, identical twins share the same genetic information ( identical twins develop from a single fertilized egg that split, so the genetic material is exactly the same in each in contrast, fraternal twins develop from two different eggs fertilized by different sperm, so the genetic material varies as with non-twin siblings). But even with identical genes, there remains an incredible amount of variability in how gene expression can unfold over the course of each twin’s life. Sometimes, one twin will develop a disease and the other will not. In one example, Tiffany, an identical twin, died from cancer at age 7, but her twin, now 19 years old, has never had cancer. Although these individuals share an identical genotype, their phenotypes differ as a result of how that genetic information is expressed over time. The epigenetic perspective is very different from range of reaction, because here the genotype is not fixed and limited.
Visit this site for an engaging video primer on the epigenetics of twin studies.
Genes affect more than our physical characteristics. Indeed, scientists have found genetic linkages to a number of behavioral characteristics, ranging from basic personality traits to sexual orientation to spirituality (for examples, see Mustanski et al., 2005 Comings, Gonzales, Saucier, Johnson, & MacMurray, 2000). Genes are also associated with temperament and a number of psychological disorders, such as depression and schizophrenia. So while it is true that genes provide the biological blueprints for our cells, tissues, organs, and body, they also have significant impact on our experiences and our behaviors.
Let’s look at the following findings regarding schizophrenia in light of our three views of gene-environment interactions. Which view do you think best explains this evidence?
In a study of people who were given up for adoption, adoptees whose biological mothers had schizophrenia and who had been raised in a disturbed family environment were much more likely to develop schizophrenia or another psychotic disorder than were any of the other groups in the study:
- Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in disturbed family environments, 36.8% were likely to develop schizophrenia.
- Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in healthy family environments, 5.8% were likely to develop schizophrenia.
- Of adoptees with a low genetic risk (whose mothers did not have schizophrenia) and who were raised in disturbed family environments, 5.3% were likely to develop schizophrenia.
- Of adoptees with a low genetic risk (whose mothers did not have schizophrenia) and who were raised in healthy family environments, 4.8% were likely to develop schizophrenia (Tienari et al., 2004).
The study shows that adoptees with high genetic risk were especially likely to develop schizophrenia only if they were raised in disturbed home environments. This research lends credibility to the notion that both genetic vulnerability and environmental stress are necessary for schizophrenia to develop, and that genes alone do not tell the full tale.
How Much Sleep Is Recommended for Each Age Group?
The recommended sleep times are broken down into nine age groups.
|Age Range||Recommended Hours of Sleep|
|Newborn||0-3 months old||14-17 hours|
|Infant||4-11 months old||12-15 hours|
|Toddler||1-2 years old||11-14 hours|
|Preschool||3-5 years old||10-13 hours|
|School-age||6-13 years old||9-11 hours|
|Teen||14-17 years old||8-10 hours|
|Young Adult||18-25 years old||7-9 hours|
|Adult||26-64 years old||7-9 hours|
|Older Adult||65 or more years old||7-8 hours|
In each group, the guidelines present a recommended range of nightly sleep duration for healthy individuals. In some cases, sleeping an hour more or less than the general range may be acceptable based on a person’s circumstances.
6 Techniques to Force Yourself to Sleep
Inhaling Through the Left Nostril
This is a yoga technique that’s used to promote calmness and reduce blood pressure. To perform this technique, lay down on the left side of your body. Rest your index finger lightly upon your right nostril to hold it closed, then inhale deeply through your left nostril. This method is especially helpful when you’re feeling overheated, or you’re coping with menopausal hot flashes. This is one of many breathing techniques suggested by Andrew Weil, M.D. on his website.
Trying to Stay Awake Instead
It might sound counter-intuitive, but there’s good science behind this technique. When you’re having trouble getting to sleep quickly, your body sends signals to your brain that something is wrong. This was a useful reaction earlier in our human evolution, when it alerted us to potential dangers and/or illness, but when it’s preventing a good night’s sleep it’s downright annoying. The method is simple: keep your eyes open wide, and repeat to yourself some variation of the phrase “I will not go to sleep! The funny thing about your brain is that it doesn’t really understand how to process negative requests. To illustrate this, let’s perform a simple exercise:
Don’t think about hamburgers and french fries. What came to your mind just then? I’m willing to bet that it was a juicy hamburger and some tasty fresh-out-of-the-oil french fries (apologies to any vegans who are reading this list of suggestions for how to make yourself fall asleep instantly). This technique, and techniques like it, are actually so common now that there’s a name for the phenomenon: ironic process theory. Think of the “trying to stay awake” method as reverse psychology for your own brain. Or…don’t think of it that way–whichever works best for you!
Squeeze & Release
Tension and stress in your muscles create conditions that make it nearly impossible for your body to sleep. The Sleep Foundation lists physical and mental stress as one of the most common causes of insomnia. One way to relieve this tension is to lay on your back, breath slowly and deeply through your nose, then squeeze your toes as tightly as you can, then simply release the pressure. Now you can repeat this process, moving upward through the various muscles in your body–you should perform this squeeze & release technique even with muscles that don’t feel tense.
After you’ve squeezed and released your toes, do the same exercise with your calves, then your buttocks, then your abdominal muscles, and so on until you’ve worked your way up to the neck. For maximum effectiveness, throughout this technique, you should focus on maintaining steady, deep breaths.
Perform a “Rewind” of Your Day
Do you have a boring job? (It’s OK, you can be honest with us.) Even if you don’t, you probably at least have a few aspects of your job that nearly bore you to sleep. Wondering what this has to do with how to force yourself to sleep? You can use mundane mental tasks to put yourself to sleep. Here’s one that many sleep professionals recommend: once you’re in bed, close your eyes and begin methodically rewinding the events of the day, starting with the moments before you got in bed, rewinding as far as you can until you sleep. Try to remember as many minute details as you can. If you’re doing it right, you should be asleep before you can even rewind all the way back to lunch.
Let Your Imagination Run Wild
Visualizations are a powerful form of meditation, and a useful tool in the fight against sleepless nights. To make these meditations more realistic (and useful), you should try to imagine a variety of sensations, related to at least three different senses. Imagine, for example, that you’re walking through a forest: what does it smell like? What does the trail feel like under your feet? Is it a bright, sunny day, or is it a little chilly and overcast? See what we mean? You’re probably familiar with the idea of “going to a happy place”–it’s a useful visualization for stress relief, which also makes it an effective tool when it comes to how to force yourself to sleep. If visualizations aren’t your thing, Psychology Today recommends silent meditation techniques to calm the mind. Their article provides many useful resources for the sleep-deprived masses.
Hum Quietly to Yourself
Did you know that humming is a yogic technique? OK, granted this might not work too well if you share your bed, but if you’re flying solo, or if you have an understanding or earplug-owning significant other, humming is a powerful way to calm your body and relieve stress. Even if you can’t try this technique in bed, you can use it to unwind before bed somewhere you feel comfortable. You don’t need to hum a tune (in fact, you probably shouldn’t), just calmly sound a note. Keep your jaw relaxed and focus on the feeling of the breath that’s passing through your lips. Focus even on the source of this breath and this sound, deep in your diaphragm.
Action Steps To Take (Before Going to Bed)
While these methods are effective methods to promote restfulness in your mind and body, there are some steps you should take to make sure your body can sleep faster. If you follow these steps and find the right technique from the list above, we’re sure that you’ll never struggle your way to sleep again. If you’re having trouble instituting any of these changes, we recommend perusing some of these quotes about life and doing some soul-searching about your current situation.
Set a Bedtime for Yourself
It might sound silly to have a “bedtime” as an adult, but your body functions at its optimal level when you fall asleep before midnight and wake up relatively early. You don’t have to be extremely strict, but you should have a general guideline of when you need to sleep. If your schedule or your personal responsibilities can’t accommodate this, you need to do your best to get quality sleep in a dark environment.
Avoiding Screens and Bright Lights
You should avoid electronics and bright screens for at least a half-hour before you go to bed. Our bodies still haven’t adjusted to these technologies–bright lights still trigger a “daytime” response from our brains. Addictions to technology throw our dopamine cycle out of whack, hurting our ability to focus and stay present. Avoiding screen time at night one of the most effective ways to return to balance in the brain. If you have dimmer switches throughout your home, consider dimming the lights a little bit as it gets later. It sounds simple, but your brain can be easier to trick than you might think.
Avoid Your Bedroom
During the day, you shouldn’t spend much time in your bedroom. Your brain should associate your bedroom primarily with sleep.
Limit Caffeine and Alcohol Consumption
This should go without saying, but limit caffeinated beverages after noon or so. You also shouldn’t drink alcohol very frequently if you want quality sleep.
Don’t Eat Before Bed
The experts at Health recommend avoiding large meals before bed, but there are a few surprising foods they also recommend avoiding for a more restful sleep. Here are some foods they also recommend avoiding for a more restful sleep
We hope you found these techniques and tips useful in your quest to learn how to make yourself fall asleep instantly. If you have any questions, comments, or sleep techniques of your own, feel free to share them with us below! Thanks for reading.
4 COGNITION AND THE GUT MICROBIOME
The gut microbiota has been shown to interact with host cognition in numerous laboratory animal model studies. Germ-free animals have shown reduced anxiety-like behaviour as well as changes in NMDA receptor subunits in the amygdala and increased hippocampal brain-derived neurotrophic factor (a protein associated with neurogenesis Neufeld, Kang, Bienenstock, & Foster, 2011 ) and antimicrobial administration increased hippocampal expression of brain-derived neurotrophic factor (Bercik et al., 2011 ). Consistent with this impact upon the hippocampus, germ-free rodents have been shown to have impaired short-term recognition and working memory (Gareau et al., 2010 ). Germ-fee animals have also displayed altered social behaviour (Arentsen, Raith, Qian, Forssberg, & Diaz-Heijtz, 2015 Desbonnet, Clarke, Shanahan, Dinan, & Cryan, 2014 ), and intriguingly, Desbonnet et al. found that recolonisation restored social preference but not social cognition. Furthermore, maternal high-fat diet had a negative impact on mice offspring's social behaviour that was reversed by treatment with Lactobacillus reuteri (Buffington et al., 2016 ). Such changes could be attributable to neurological changes such as increased myelination in the prefrontal cortex in germ-free mice, a change which could be reversed by the restoration of the microbiota (Hoban et al., 2016 ).
Research in animal models will be crucial in guiding research in the human brain–gut–microbiome axis, as the impact of microbiota on specific brain regions and aspects of animal behaviour will help in the selection of cognitive tasks to explore. Research employing animal models will also be useful in identifying which bacteria may be of particular relevance. For example, in rodent models, a specific strain of Bifidobacterium longum was found to alter cognition (Savignac, Tramullas, Kiely, Dinan, & Cryan, 2015 ), as well as stress-related behaviour and physiology (Savignac, Kiely, Dinan, & Cryan, 2014 ), and a similar profile of effects was subsequently observed in humans who were given this strain (Allen, Hutch, et al., 2016 see section below on psychobiotics). However, despite promising results from preclinical investigation (Bravo et al., 2011 ), such effects were not evident when healthy human volunteers consumed a strain of Lactobacillus (Kelly, Allen, et al., 2017 ) this suggests differences between bacterial strains in the degree to which they can be translated from laboratory animal models to humans.
Despite this potential for translational application of research findings from laboratory animal models to human psychology, there has been a relative lack of research linking the overall structure and composition of the microbiome to cognition in humans. Nonetheless, evidence that cognitive performance in humans can be moderated by probiotics (see section below) is further indicative of a role of the microbiota in cognition. As some of these effects may be relatively subtle, particularly in healthy young adults (Allen, Hutch, et al., 2016 Tillisch, 2014 ), there is clearly scope for cognitive psychologists to investigate further how specific aspects of cognition may be affected by the brain–gut–microbiome axis, using well-specified measures of cognitive performance. For example, although some evidence suggests that probiotic intervention can alter sustained attention (Chung et al., 2014 ), overall sustained attention performance may not be as informative as time-on-task data that tracks sustained attention performance over time, when performance is likely to deteriorate (Allen & Smith, 2012 Mackworth, 1948 Verster & Roth, 2013 ).
Given the mounting preclinical evidence for its impact upon psychological function, the gut microbiota has been provocatively described as part of the unconscious system(s) influencing behaviour (Dinan, Stilling, Stanton, & Cryan, 2015 ), along with other physiological processes upon which a person may lack insight into, but nonetheless impact upon human psychology. We may further speculate that changes in the gut microbiota (e.g., due to antibiotic use), which are sufficient to alter consciously tangible factors such as bowel habit or gastrointestinal discomfort, may in turn alter interpretations of thoughts or emotions, consistent with the view that visceral factors impact upon human psychology (e.g. Loewenstein, 1996 ). The gut may thus have both conscious as well as unconscious effects upon psychological processes. These conscious effects are more likely to impact as an affect heuristic (Slovic, Finucane, Peters, & MacGregor, 2007 ) visceral factors act as a heuristic or mental shortcut (a Type 1 process), rather than as formal or logical information processing (Type 2 processes). They may nevertheless impact upon Type 2 processes for example, by disrupting them. Models surrounding the interaction between Type 1 and Type 2 processes in thinking (e.g., Evans, 2007 Pennycook, Fugelsang, & Koehler, 2015 ) will be informative with regard to how the Type 1 factors stemming from the gut may impact upon Type 2 processing.
Regulation Of Physical Growth
The process of physical growth is a complex one, influenced by genetic, hormonal, and environmental factors. Genes offer a potential range for achieving physical size and shape, and the environment partly determines the eventual growth within that range.
Genes do not influence growth directly. They produce proteins that regulate a genetically inherited pattern of growth, mediated by the endocrine and neurological systems. In essence, the endocrine system— the system of glands under neural control responsible for the release of regulatory chemicals—provides the biochemical environment in which genes act. For example, the adolescent growth spurt cannot occur without the release of sufficient quantities of growth and sex-specific hormones into the blood. Harmful environmental insults cause a reduction in the release of growth hormone and other hormones, resulting in reduced growth. To this extent, the endocrine system acts as an intermediary between the action of the genes and the influence of the environment.
Although genes and the endocrine system have significant influence on the regulation of physical growth, environmental factors—those that are nongenetic and external to the organism—can also account for some of the differences between individuals. Unfavorable environmental conditions, such as nutrition, negative psychological and social experiences, and pollutants, can start to affect growth adversely from shortly after the moment of conception, and continue throughout the life span.
The effects of harmful environmental conditions on growth seem to be dependent on the severity and duration of the problem, as well as the age at which it occurs. Young children are particularly vulnerable to such insults. However, there is some evidence to suggest that, when the insult is removed and adequate nutrition is available, retardation of growth is usually followed by a period of catch-up growth, during which the individual rapidly returns to or approaches a normal rate of growth. A useful analogy for this period of catch-up was provided by the British geneticist, C. H. Waddington, who compared physical growth to the movement of a ball down a valley floor. He suggested that an insult may knock the ball away from a central pathway, and the velocity of its movement will then reduce. Once the insult is corrected, though, the ball returns toward the valley floor at an increased speed, upon which normal velocity recommences. If the insult is not corrected, perhaps because of continued poor diet, the individual may resume growth at a relatively slower rate, and skeletal maturation may be delayed, extending the period of growth. Scholars disagree regarding the long-term effects of harmful environmental conditions during infancy and childhood, but there is some evidence to suggest that severe difficulties can result in negative lasting effects. In most cases, however, it seems to be the case that growth merely slows down in response to harmful conditions, and waits for better times.
Because environmental factors rarely operate in isolation, it can be difficult to quantify the precise relationship between specific influences and physical growth. Nevertheless, there are certain factors that have well-documented effects on physical growth, including nutrition, social and environmental status, psychological stress, and pollutants.
Table 4 Common Measurements of Individual Growth
Although the effects of poor nutrition can be experienced at all stages of development, including during the prenatal growth, infancy and early childhood represent the periods during which the developing child’s system is unusually sensitive to malnutrition. This seems to be, in part, because the first years of life witness the most rapid growth. International studies suggest that about half of all deaths during the first 5 years result from the effects of poor nutrition and the associated inability to fight infectious diseases.
Adolescence is another period when individuals are especially vulnerable to the harmful effects of malnutrition. Nutritional needs are greater during this period than at any other time of life, and although the rate of proportionate growth is somewhat less than during the early years, it persists for much longer. As is well known, adolescence is a time when young people experiment with food choices, and inappropriate choices can have profound and long-lasting effects. Conditions such as anorexia nervosa (a disorder characterized by an abnormal fear of becoming obese) and bulimia nervosa (an eating disorder, in which binge eating is often followed by feelings of guilt and fasting) are especially common among adolescent girls and can seriously threaten both health and physical growth. Aside from retarding an individual’s rate of growth, inappropriate diet can also have harmful effects on skeletal development, and insufficient food intake has been associated with the development of osteoporosis, or brittle bones, in women.
Adequate nutrition is of fundamental importance to physical growth and development. A reduction in the rate of growth is one of the first responses to restricted food intake, and in countries where food is persistently limited, growth delays occur, and children tend to be shorter and lighter than in countries with adequate food supplies. In fact, so strongly associated are growth and nutrition that measurement of physical growth is one of the most widely used indices of nutritional status in children.
Social and Economic Status
Children from poorer families are generally shorter and lighter than their peers in higher-income families. They also consume less food. The timing of growth, rather than growth itself, seems to be most affected by social and economic factors for example, the onset of puberty occurs earlier in individuals from wealthier groups than those from poorer groups. Studies of preschoolers have reported differences in height, weight, skin-fold thickness, and musculature in favor of children from high social and economic status families. By the time they reach adulthood, much of the difference is reduced or even cancelled. Social and economic factors are most evident among males. In fact, most environmental influences seem to affect males more strongly than females. The reasons for such differences are unclear.
There is considerable evidence that extreme stress can slow physical growth and development. The mechanisms involved in such effects are unclear, although stress may negatively affect the secretion of growth hormones. A cluster of factors like maternal care, social isolation, parental substance abuse, and sexual abuse are linked to psychological and emotional ill health. Recent research has also indicated that some children are genetically predisposed to stress and respond to it in an extreme and prolonged manner that results in restricted growth.
Physical growth is sensitive to several pollutants, including lead, air pollution, certain organic compounds, and tobacco smoke. Of course, pollutants are somewhat unavoidable in the modern world, but levels of pollution vary considerably, and so its effects will be different among different groups. To take only one example, smoking by the mother during pregnancy is well known to affect both birth weight and an infant’s subsequent growth. It also seems that living in a home with smoking parents is related to reduced height and weight throughout infancy and childhood. The insult to weight seems to be corrected as the individual moves toward adolescence the deficit in height is probably never made up.
10 Limits to Human Perception . and How They Shape Your World
Every human has limits. You can only run so fast, jump so high, and go for so long without water. But what about restrictions upon our five senses, those tools that we use to perceive and understand our surroundings? Here are ten limitations on human perception that have a direct impact on how we understand the world.
About one quarter of the human brain is involved in visual processing - more than any other sense. Arguably the most closely studied of the five main senses, the Society for Neuroscience claims that more is known about vision than any other vertebrate sensory system.
10. Field of View
A pair of healthy human eyes has a total field of view of approximately 200 degrees horizontally — about 120 degrees of which are shared by both eyes, giving rise to what's known as binocular vision — and 135 degrees vertically, (though these values tend to decrease with age). This is due to the fact that both of our eyes are positioned more or less on the front of our heads, as opposed to the sides.
Having eyes positioned on the sides of one's head is common in prey species, and while it certainly increases an animal's total field of view, it's often at the expense of sharper binocular vision (see the helpful chart featured here, which shows the differences in vision between pigeons, whose eyes reside on the sides of their heads, and owls, who, like humans, sport front-facing peepers). Then again, if one of your primary concerns as an animal is to avoid being eaten (as opposed to seeing what, precisely, is trying to eat you), that's a pretty reasonable tradeoff.
9. Angular Resolution
Angular resolution is one of the terms used to describe an optical device's ability to distinguish very small details. If you want to talk about the smallest thing perceivable by the human eye, it makes sense to do so in terms of angular resolution.
Angular resolution is commonly measured in units known as arc minutes and arc seconds, which correspond to 1/60th and 1/3600th of a single degree in your field of view, respectively. The typical set of human eyes has an angular resolution on the order of one arc minute, give or take a few arc seconds. If you were to draw a line measuring a third of a millimeter wide on a piece of paper and hold it at arm's length, the line would cover about 1 arc minute of your vision.
8. The Blind Spot
The human eye is lined with photoreceptor cells that it uses to perceive light. Visual information received by these photoreceptor cells is relayed to the brain via the optic nerve. The only problem is that the optic nerve actually passes through part of photoreceptors lining the inside of the eye, creating a small, receptor-less patch where it's impossible to detect light.
Normally this isn't an issue. We've got two eyes, and our brains are incredibly good at using the visual information gathered from each eye to fill in the gaps left by the other's blind spot. But things get screwy when you have to rely on just one eye. Try this optical illusion on for size to see what happens when your brain can't find the visual information lost to your eye's blind spot.
This amazing optical illusion video will make a man's head disappear
This video uses your eye's built-in blind spot to trick your brain into making a man's head…
7. The "Visible" Spectrum
Probably the most well-known of human sensory limitations, the typical human eye is only capable of perceiving light at wavelengths between 390 and 750 nanometers. Of course, calling it the "visible" spectrum is a bit of a misnomer, as plenty of animals are capable of perceiving light with frequencies outside this relatively narrow band of electromagnetic radiation.
Commonly listed alongside vision as one of the most important of the human senses, hearing is is a vital part of everything from communication to risk-avoidance.
6. Hearing Range
Among young, healthy humans, the range of frequencies that can be picked up by the human ear is usually cited as 20 — 20,000 Hz however, the upper limit on that range tends to decrease pretty steadily with age.
5. Absolute Threshold of Hearing
Your absolute threshold of hearing is the quietest sound your ears are capable of picking up when there are no other sounds around to mask its perception. This threshold varies from person to person, changes with age, and is largely dependent on the frequency of the noise being perceived. It's also quieter than you might think.
This chart, borrowed from a comparative analysis of published threshold data , shows how the lower limit of a person's hearing threshold (measured in decibels ) changes as a function of frequency. In this particular graph, data has been collected on test subjects between the ages of 18 and 55, tested at frequencies between 125 and 12,000 Hz, to show that the lower limit of detectable sound is not zero decibels (as it is commonly depicted in figures like the one below), but around -5 decibels.
That being said, as the percentiles listed on the right hand side of the chart make clear, the ability to hear noises as quiet as -5 dB is pretty rare (among males and females alike, only around one person in ten will be able to hear sounds quieter than zero decibels). In actuality, the average hearing threshold is, in fact, between 0 and 5 decibels.
Taste & Smell
These two senses rely on different sensory organs, but are very closely related when someone loses his or her sense of smell, for example, their sense of taste is dramatically diminished.
4. Limitations in Wine Tasting
The sense of taste is arguably the weakest of the human senses. This is something we've talked about before your ability to "taste" wine, for example, is actually more dependent upon your sense of smell. Here's what we had to say about the limitations of taste back in March:
In what is hands down my favorite experiment on the limitations of the human palate ever performed , researcher Frédéric Brochet invited 57 wine experts to give their opinions on what appeared to be two glasses of wine - one red, and one white. The wines were actually the exact same white wine the "red" had simply been mixed with red food coloring.
The experts proceeded to describe the "red" wine in language typically reserved for characterizing reds, noting, for example, its "jamminess," or the flavors imparted by its "crushed red fruit." Incredibly, not a single expert noticed that it was, in fact, a white wine.
However, there is also evidence for the existence of so-called "supertasters" — i.e. people who are unusually sensitive to what are known as the "basic tastes," namely bitter, sweet, sour and salty.
These supertasters were discovered by Linda Bartoshuk (a pioneer in the field of psychophysics, the study of how stimuli such as taste lead to subjective experience), who demonstrated that their sensitive tastes were correlated with higher densities of fungiform papillae, the bumps on the tongue containing taste buds. That being said, the ability to objectively gauge intensity of flavor perception has remained a significant challenge in the world of psychophysics, making absolute threshold tests (like those used to determine the limits of human hearing) difficult to perform. [Supertaster image via Science ]
2. Odor Detection Threshold
Like taste thresholds, the limits of odor detection have proven difficult to pin down. Writing in the journal Chemical Senses , Dr. Thomas Hummel (an ear nose and throat doctor) describes some of the challenges involved:
Tests for the assessment of olfactory functions are numerous. However, in the clinical practice of otorhinolaryngology [the study of ear, nose and throat function] of neurology few, if any, of them are actually used. The reasons may be found int he inconsistency of some tests, the lack of normative data, the time needed for adnimistration and the limited availability of these tests.
How Long Can Humans Stay Awake?
The easy experimental answer to this question is 264 hours (about 11 days). In 1965, Randy Gardner, a 17-year-old high school student, set this apparent world-record for a science fair. Several other normal research subjects have remained awake for eight to 10 days in carefully monitored experiments. None of these individuals experienced serious medical, neurological, physiological or psychiatric problems. On the other hand, all of them showed progressive and significant deficits in concentration, motivation, perception and other higher mental processes as the duration of sleep deprivation increased. Nevertheless, all experimental subjects recovered to relative normality within one or two nights of recovery sleep. Other anecdotal reports describe soldiers staying awake for four days in battle, or unmedicated patients with mania going without sleep for three to four days.
The more difficult answer to this question revolves around the definition of "awake." As mentioned above, prolonged sleep deprivation in normal subjects induces altered states of consciousness (often described as "microsleep"), numerous brief episodes of overwhelming sleep, and loss of cognitive and motor functions. We all know about the dangerous, drowsy driver, and we have heard about sleep-deprived British pilots who crashed their planes (having fallen asleep) while flying home from the war zone during World War II. Randy Gardner was "awake" but basically cognitively dysfunctional at the end of his ordeal.
In the case of rats, however, continuous sleep deprivation for about two weeks or more inevitably caused death in experiments conducted in Allan Rechtschaffens sleep laboratory at the University of Chicago. Two animals lived on a rotating disc over a pool of water, separated by a fixed wall. Brainwaves were recorded continuously into a computer program that almost instantaneously recognized the onset of sleep. When the experimental rat fell asleep, the disc was rotated to keep it awake by bumping it against the wall and threatening to push the animal into the water. Control rats could sleep when the experimental rat was awake but were moved equally whenever the experimental rat started to sleep. The cause of death was not proven but was associated with whole body hypermetabolism.
In certain rare human medical disorders, the question of how long people can remain awake raises other surprising answers, and more questions. Morvans fibrillary chorea or Morvans syndrome is characterized by muscle twitching, pain, excessive sweating, weight loss, periodic hallucinations, and severe loss of sleep (agrypnia). Michel Jouvet and his colleagues in Lyon, France, studied a 27-year-old man with this disorder and found he had virtually no sleep over a period of several months. During that time he did not feel sleepy or tired and did not show any disorders of mood, memory, or anxiety. Nevertheless, nearly every night between 9:00 and 11:00 p.m., he experienced a 20 to 60-minute period of auditory, visual, olfactory, and somesthetic (sense of touch) hallucinations, as well as pain and vasoconstriction in his fingers and toes. In recent investigations, Morvans Syndrome has been attributed to serum antibodies directed against specific potassium (K + ) channels in cell and nerve membranes.
Another rare disorder, Fatal Familial Insomnia (FFI), is an autosomal dominate disease that is invariably fatal after about six to 30 months without sleep. FFI is probably misnamed because death results from multiple organ failure rather than sleep deprivation. The pathological processes include degeneration of the thalamus and other brain areas, over-activity of the sympathetic nervous system, hypertension, fever, tremors, stupor, weight loss, and disruption of the body's endocrine systems. FFI belongs to a class of infectious prion diseases that include Mad Cow Disease.
A sleep expert explains what happens to your body and brain if you don't get enough sleep
We certainly know that a lack of sleep will actually prevent your brain from being able to initially make new memories, so it's almost as though without sleep the memory inbox of the brain shuts down and you can't commit new experiences to memory. So those new incoming informational emails are just bounced, and you end up feeling as though you're amnesiac. You can't essentially make and create those new memories.
We also know that a lack of sleep will lead to an increased development of a toxic protein in the brain that is called beta-amyloid and that is associated with Alzheimer's disease because it is during deep sleep at night when a sewage system within the brain actually kicks in to high gear and it starts to wash away this toxic protein, beta-amyloid.
So if you're not getting enough sleep each and every night, more of that Alzheimer's-related protein will build up. The more protein that builds up, the greater your risk of going on to develop dementia in later life.
What are the effects of sleep deprivation on the body? Well, there are many different effects. Firstly, we know that sleep deprivation affects the reproductive system. We know that men who are sleeping just five to six hours a night have a level of testosterone which is that of someone ten years their senior. So a lack of sleep will age you by almost a decade in terms of that aspect of virility and wellness.
We also know that a lack of sleep impacts your immune system. So after just one night of four to five hours of sleep, there is a 70% reduction in critical anticancer-fighting immune cells called natural killer cells. And that's the reason that we know that short sleep duration predicts your risk for developing numerous forms of cancer. And that list currently includes cancer of the bowel, cancer of the prostate, as well as cancer of the breast.
In fact, the link between a lack of sleep and cancer is now so strong that recently the World Health Organization decided to classify any form of nighttime shift work as a probable carcinogen. So in other words, jobs that may induce cancer because of a disruption of your sleep rate rhythms.
We also know that a lack of sleep impacts your cardiovascular system because it is during deep sleep at night that you receive this most wonderful form of effectively blood pressure medication. Your heart rate drops, your blood pressure goes down.
If you're not getting sufficient sleep, you're not getting that reboot of the cardiovascular system, so your blood pressure rises. You have, if you're getting six hours of sleep or less, a 200% increased risk of having a fatal heart attack or stroke in your lifetime.
There is a global experiment that is performed on 1.6 billion people twice a year and it's called daylight savings time. And we know that in the spring, when we lose one hour of sleep, we see a subsequent 24% increase in heart attacks the following day.
Another question, perhaps, is what is the recycle rate of a human being? How long can we actually last without sleep before we start to see declines in your brain function or even impairments within your body? And the answer seems to be about 16 hours of wakefulness.
Once you get past 16 hours of being awake, that's when we start to see mental deterioration and physiological deterioration in the body. We know that after you've been awake for 19 or 20 hours, your mental capacity is so impaired that you would be as deficient as someone who was legally drunk behind the wheel of a car. So if you were to ask me what is the recycle rate of a human being, it does seem to be about 16 hours and we need about eight hours of sleep to repair the damage of wakefulness. Wakefulness essentially is low-level brain damage.
EDITOR'S NOTE: This video was originally published on December 26, 2017. Lamar Salter contributed reporting on a previous version of this article.
Pushing The Limits Of The Human Body
Humanity has toppled scores of world records over the past few decades, but how much more progress can we make?
After Olympic sprinter Usain Bolt broke the 100-meter world record at the 2008 Olympics, Mark Denny, a biologist at Stanford University, wondered: Had “Lightning Bolt” sprinted as fast as a human can go? After analyzing records back to the 1920s, Denny predicts humans may one day cover 100m in only 9.48 seconds, or .10 seconds faster than Bolt’s current record of 9.58 seconds––a lot speedier in a sport where differences are measured by the 100th of a second. PRO TIPS: How To Improve Your Fitness Even when your brain says no way, there are tricks to coax your muscles into running faster and biking longer. Race Against A Worthy Rival In a 2012 study, English cyclists were told to pedal as fast as they could. Then they raced against a computerized competitor going one percent faster, and kept up. So it’s a good idea to train with someone better. Breathe Easy, Or Hard Tim Noakes at the University of Cape Town had runners take a maximal oxygen consumption test that started surprisingly tough and got easier. He found that oxygen levels actually don’t limit performance. Gargle Gatorade In a 2008 study, cyclists gargled sugar water and spat it out, tricking their brains into thinking they’d ingested carbs. Swilling drinks stimulates taste-bud receptors, boosting the metabolism. Illustrations by Muti
We humans are programmed to grow stronger, faster, and smarter to climb higher, live longer, and populate every last inch of real estate. We’ve toppled scores of world records over the past few decades, but how much more progress can we make? No matter how we enhance our natural capabilities, our potential is bound by certain scientific principles—laws of physics, biomechanics, and thermodynamics—that don’t yield to human ambition. We asked scientists to define where, exactly, those boundaries lie, and to provide some take-home tips that’ll help you stretch your own potential.
_This article originally appeared in the September 2014 issue of _Popular Science.