by Brian Dunning
Filed under Environment, General Science, Health
A study of 32 participants found that long-term memory improved after listening to binaural beats in the beta range (20 Hz), but decreased after listening to theta (5 Hz) binaural beats. However, in another study, participants who listened to 15 min of theta (5 Hz) binaural beats had better short-term verbal memory 29. Oct 12, 2020 Proponents: May reduce anxiety and improve mood May improve focus, attention, and memory May increase creativity and cognitive flexibility May help you enter a meditative state Linked to improved sleep quality.
Skeptoid Podcast #352
March 5, 2013
Podcast transcript | Subscribe
Also available in Russian
Listen:
https://skeptoid.com/audio/skeptoid-4352.mp3
It's increasingly hard to find a web page dedicated to the sales of alternative medicine products or New Age spirituality that does not cite the Schumann resonances as proof that some product or service is rooted in science. This mysterious number of 7.83 comes up again and again in sales pitches, as a sort of miracle frequency that can bring you health and wellness. Today we're going to see what the Schumann resonances actually are, how they formed and what they do, and see if we can determine whether they are, in fact, related to human health.
In a nutshell, the Schumann resonances are the name given to the resonant frequency of the Earth's atmosphere, between the surface and the densest part of the ionosphere. They're named for the German physicist Winfried Otto Schumann (1888-1974) who worked briefly in the United States after WWII, and predicted that the Earth's atmosphere would resonate certain electromagnetic frequencies. The closed space inside a bottle has a resonant frequency which becomes audible when you blow across it:
Your browser does not support the audio tag.
This particular bottle has a resonant frequency of about 196 Hz. That's the frequency of sound waves that most efficiently bounce back and forth between the sides of the bottle, at the speed of sound, propagating via the air molecules. Electromagnetic radiation is similar, except the waves travel at the speed of light, and do not require a medium like air molecules. The speed of light is a lot faster than the speed of sound, but the electromagnetic waves have a lot further to go between the ground and the ionosphere than do the sound waves between the sides of the bottle. This atmospheric electromagnetic resonant frequency is 7.83 Hz, which is near the bottom of the ELF frequency range, or Extremely Low Frequency. The atmosphere has its own radio equivalent of someone blowing across the top of the bottle: lightning. Lightning is constantly flashing all around the world, many times per second; and each bolt is a radio source. This means our atmosphere is continuously resonating with a radio frequency of 7.83 Hz, along with progressively weaker harmonics at 14.3, 20.8, 27.3 and 33.8 Hz. These are the Schumann resonances. It's nothing to do with the Earth itself, or with life, or with any spiritual phenomenon; it's merely an artifact of the physical dimensions of the space between the surface of the Earth and the ionosphere. Every planet and moon that has an ionosphere has its own set of Schumann resonances defined by the planet's size.
The amount of resonance fluctuates as the ionosphere becomes more or less dense, which depends largely on the amount of solar radiation striking it. At night, that part of the ionosphere that's in the Earth's shadow thins out. Another influence is that the world's three lightning hotspots — Asia, Africa, and South America — also follow a day/night cycle, and are seasonal as well. Thus, the peaks of radio signal strength at the Schumann resonance follow a constantly shifting, but reasonably predictable, schedule.
A very important point to be aware of is that this resonated radio from lightning is a vanishingly small component of the electromagnetic spectrum to which we're all naturally exposed. The overwhelming source is the sun, blasting the Earth with infrared, visible light, and ultraviolet radiation. All natural sources from outer space, and even radioactive decay of naturally occuring elements on Earth, produce wide-spectrum radio noise. Those resonating in the Schumann cavity are only a tiny, tiny part of the spectrum.
Nevertheless, because the Schumann resonance frequencies are defined by the dimensions of the Earth, many New Age proponents and alternative medicine advocates have come to regard 7.83 Hz as some sort of Mother Earth frequency, asserting the belief that it's related to life on Earth, despite its being so tiny and lost among all the other, stronger parts of the electromagnetic spectrum. Often we find that New Age beliefs are often based more on what seems emotionally satisfying than on sound science.
The most pervasive of all the popular fictions surrounding the Schumann resonance is that it is correlated with the health of the human body. There are a huge number of products and services sold to enhance health or mood, citing the Schumann resonance as the foundational science. Before looking at some of these claims in detail, it's noteworthy that neither Schumann resonances, electromagnetic radiation, or the Earth's ionosphere are mentioned in any medical or anatomical textbooks. There is no detectable or theoretically predicted relationship between either ELF radio or the number 7.83 and the health of human body. But let's look at some of the claims.
Many marketers of jewelry that claims to provide health or sports performance benefits cite the Schumann resonance as the science behind their claim. A notable example is the Power Balance bracelets. Tom O'Dowd, formerly the Australian distributor, said that the mylar hologram resonated at 7.83 Hz. When the bracelet was placed within the body's natural energy field, the resonance would 'reset' your energy field to that frequency. Well, there were a lot of problems with that claim. First of all, 7.83 Hz has a wavelength of about 38,000 kilometers. This is about the circumference of the Earth, which is why its atmospheric cavity resonates at that frequency. 38,000 kilometers is just a little bit bigger than a 1 or 2cm hologram; there's no way that something that tiny could resonate such an enormous wavelength. O'Dowd's sales pitch was implausible, by a factor of billions, to anyone who understood resonance.
This same fact also applies to the human body. Human beings are so small, relative to a radio wavelength of 38,000 kilometers, that there's no way our anatomy could detect or interact with such a radio signal in any way.
Proponents of binaural beats cite the Schumann frequency as well. These are audio recordings which combine two slightly offset frequencies to produce a third phantom beat frequency that is perceived from the interference of the two. Here is a common binaural beat recording that produces a beat frequency of 7.83 Hz:
Your browser does not support the audio tag.
Claims for how this benefits the body are diverse, but most either say something generally similar to what O'Dowd said, or they would claim to change your brain's encephalogram, which they say is a beneficial thing to do. Brain waves, the fluctuations of current in the brain as measured at the scalp by an electroencephalogram, can range from near zero up to about 100 Hz during normal activity, with a typical reading near the lower end of the scale. This happens to overlap 7.83 — suggesting the aforementioned pseudoscientific connection between humans and the Schumann resonance — but with a critical difference. An audio recording is audio, not radio. It's the physical oscillation of air molecules, not the propagation of electromagnetic waves. The two have virtually nothing to do with each other. Audio waves do not affect radio waves, and vice versa. So by no science that's understood would we expect an audio tone to cause a brain's activity to change its frequency to match.
417 Hz Benefits
There's a complete Skeptoid episode on binaural beats that addresses the claims in greater detail, and examines some of the research done.
I found one website, EarthCalm.ca (just as one example among many), that says:
Scientific research has recently determined how the human body receives and uses the important information from the Earth's field: 7 billion crystalline magnetites in the human brain, in addition to DNA and the pineal gland are meant to receive guiding information from the band of electromagnetic frequencies that extends from the Earth's crust to the ionosphere (Schumann Resonances). Today, the Earth's field is polluted with man-made frequencies, so the human body instead receives 'junk' produced by AC electricity and wireless technology.
Variations on this specific claim are fairly ubiquitous, that our bodies' energy fields need to interact with the Schumann resonance but can't because of all the interference from modern society. It's all complete and utter nonsense. Human bodies do not have an energy field, in fact there's not even any such thing as an energy field. Fields are constructs in which some direction or intensity is measured at every point: gravity, wind, magnetism, some expression of energy. Energy is just a measurement; it doesn't exist on its own as a cloud or a field or some other entity. The notion that frequencies can interact with the body's energy field is, as the saying goes, so wrong it's not even wrong.
Another really common New Age misconception about the Schumann resonance is that it is the resonant frequency of the Earth. This is also completely wrong. Take another listen to blowing across the bottle:
Your browser does not support the audio tag.
The space inside the bottle resonates at 196 Hz, a G on the musical scale. But listen when I tap the bottle itself:
Your browser does not support the audio tag.
The resonant frequency of the glass bottle itself is about 3520 Hz, which is an A on the musical scale. Two completely different notes. That's because the bottle and the space inside are two different things, with not necessarily any relationship between them. Similarly, there's no reason to expect the Earth's electromagnetic resonant frequency to bear any similarity to the Schumann resonance. But, furthermore, the Earth probably doesn't even have a resonant electromagnetic frequency. Each of the Earth's many layers is a very poor conductor of radio; combined all together, the Earth easily absorbs just about every frequency it's exposed to. If you've ever noticed that your car radio cuts out when you drive through a tunnel, you've seen an example of this.
Now the Earth does, of course, conduct low-frequency waves of other types. Earthquakes are the prime example of this. The Earth's various layers propagate seismic waves differently, but all quite well. Seismic waves are shockwaves, a physical oscillation of the medium. Like audio waves, these are unrelated to electromagnetic radio waves. Each and every major structure within the Earth — such as a mass of rock within a continent, a particular layer of magma, etc. — does have its own resonant frequency for seismic shockwaves, but there is (definitively) no resonant electromagnetic frequency for the Earth as a whole.
So our major point today is that you should be very skeptical of any product, service, article, website, or merchant who uses the Schumann resonance, in any way, as part of a sales pitch. The Earth does not have any particular frequency. Life on Earth is neither dependent upon, nor enhanced by, any specific frequency. Most of these sales pitches are what we in the brotherhood like to call a Word Salad, sciencey-sounding language thrown together in such a way as to sound impressive to the layperson. There's plenty of sciencey goodness in understanding why and what the Schumann resonances actually are, without co-opting them to promote nonsense.
Correction: An earlier version of this incorrectly described 196 Hz as the speed at which the waves bounce back and forth between the sides of the bottle, which is wrong.
Correction: An earlier version also stated that electromagnetic waves propagate via electrons, which was an ill-conceived 'journalist's shortcut.' Electromagnetic waves do not require that electrons be present.
By Brian Dunning
Shop apparel, books, & closeouts |
Cite this article:
Dunning, B. 'Facts and Fiction of the Schumann Resonance.' Skeptoid Podcast. Skeptoid Media, 5 Mar 2013. Web. 12 Dec 2020.
References & Further Reading
Editors. 'How Radio Communication Works.' National Radio Astronomy Observatory. National Science Foundation, 17 Aug. 2008. Web. 2 Mar. 2013.
Kruszelnicki, K. 'Sceptics, energy fields and busting myths.' Dr. Karl on Triple J. ABC, 25 Nov. 2010. Web. 2 Mar. 2013.
Nickolaenko, A., Hayakawa, M. Resonances in the Earth–ionosphere cavity. Dordrecht: Kluwer Academic Publishers, 2002.
Pechony, O., Price, C. 'Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan.' Radio Science. 9 Oct. 2004, Volume 39, Number 5.
Rakov, V. Lightning: Physics and Effects. Cambridge: Cambridge University Press, 2003.
Shelikoff, M. 'Ask the Experts.' Physics and Astronomy Online. PhysLink.com, 15 Nov. 2001. Web. 2 Mar. 2013.
Copyright ©2020 Skeptoid Media, Inc. All Rights Reserved. Rights and reuse information
This particular bottle has a resonant frequency of about 196 Hz. That's the frequency of sound waves that most efficiently bounce back and forth between the sides of the bottle, at the speed of sound, propagating via the air molecules. Electromagnetic radiation is similar, except the waves travel at the speed of light, and do not require a medium like air molecules. The speed of light is a lot faster than the speed of sound, but the electromagnetic waves have a lot further to go between the ground and the ionosphere than do the sound waves between the sides of the bottle. This atmospheric electromagnetic resonant frequency is 7.83 Hz, which is near the bottom of the ELF frequency range, or Extremely Low Frequency. The atmosphere has its own radio equivalent of someone blowing across the top of the bottle: lightning. Lightning is constantly flashing all around the world, many times per second; and each bolt is a radio source. This means our atmosphere is continuously resonating with a radio frequency of 7.83 Hz, along with progressively weaker harmonics at 14.3, 20.8, 27.3 and 33.8 Hz. These are the Schumann resonances. It's nothing to do with the Earth itself, or with life, or with any spiritual phenomenon; it's merely an artifact of the physical dimensions of the space between the surface of the Earth and the ionosphere. Every planet and moon that has an ionosphere has its own set of Schumann resonances defined by the planet's size.
The amount of resonance fluctuates as the ionosphere becomes more or less dense, which depends largely on the amount of solar radiation striking it. At night, that part of the ionosphere that's in the Earth's shadow thins out. Another influence is that the world's three lightning hotspots — Asia, Africa, and South America — also follow a day/night cycle, and are seasonal as well. Thus, the peaks of radio signal strength at the Schumann resonance follow a constantly shifting, but reasonably predictable, schedule.
A very important point to be aware of is that this resonated radio from lightning is a vanishingly small component of the electromagnetic spectrum to which we're all naturally exposed. The overwhelming source is the sun, blasting the Earth with infrared, visible light, and ultraviolet radiation. All natural sources from outer space, and even radioactive decay of naturally occuring elements on Earth, produce wide-spectrum radio noise. Those resonating in the Schumann cavity are only a tiny, tiny part of the spectrum.
Nevertheless, because the Schumann resonance frequencies are defined by the dimensions of the Earth, many New Age proponents and alternative medicine advocates have come to regard 7.83 Hz as some sort of Mother Earth frequency, asserting the belief that it's related to life on Earth, despite its being so tiny and lost among all the other, stronger parts of the electromagnetic spectrum. Often we find that New Age beliefs are often based more on what seems emotionally satisfying than on sound science.
The most pervasive of all the popular fictions surrounding the Schumann resonance is that it is correlated with the health of the human body. There are a huge number of products and services sold to enhance health or mood, citing the Schumann resonance as the foundational science. Before looking at some of these claims in detail, it's noteworthy that neither Schumann resonances, electromagnetic radiation, or the Earth's ionosphere are mentioned in any medical or anatomical textbooks. There is no detectable or theoretically predicted relationship between either ELF radio or the number 7.83 and the health of human body. But let's look at some of the claims.
Many marketers of jewelry that claims to provide health or sports performance benefits cite the Schumann resonance as the science behind their claim. A notable example is the Power Balance bracelets. Tom O'Dowd, formerly the Australian distributor, said that the mylar hologram resonated at 7.83 Hz. When the bracelet was placed within the body's natural energy field, the resonance would 'reset' your energy field to that frequency. Well, there were a lot of problems with that claim. First of all, 7.83 Hz has a wavelength of about 38,000 kilometers. This is about the circumference of the Earth, which is why its atmospheric cavity resonates at that frequency. 38,000 kilometers is just a little bit bigger than a 1 or 2cm hologram; there's no way that something that tiny could resonate such an enormous wavelength. O'Dowd's sales pitch was implausible, by a factor of billions, to anyone who understood resonance.
This same fact also applies to the human body. Human beings are so small, relative to a radio wavelength of 38,000 kilometers, that there's no way our anatomy could detect or interact with such a radio signal in any way.
Proponents of binaural beats cite the Schumann frequency as well. These are audio recordings which combine two slightly offset frequencies to produce a third phantom beat frequency that is perceived from the interference of the two. Here is a common binaural beat recording that produces a beat frequency of 7.83 Hz:
Your browser does not support the audio tag.
Claims for how this benefits the body are diverse, but most either say something generally similar to what O'Dowd said, or they would claim to change your brain's encephalogram, which they say is a beneficial thing to do. Brain waves, the fluctuations of current in the brain as measured at the scalp by an electroencephalogram, can range from near zero up to about 100 Hz during normal activity, with a typical reading near the lower end of the scale. This happens to overlap 7.83 — suggesting the aforementioned pseudoscientific connection between humans and the Schumann resonance — but with a critical difference. An audio recording is audio, not radio. It's the physical oscillation of air molecules, not the propagation of electromagnetic waves. The two have virtually nothing to do with each other. Audio waves do not affect radio waves, and vice versa. So by no science that's understood would we expect an audio tone to cause a brain's activity to change its frequency to match.
417 Hz Benefits
There's a complete Skeptoid episode on binaural beats that addresses the claims in greater detail, and examines some of the research done.
I found one website, EarthCalm.ca (just as one example among many), that says:
Scientific research has recently determined how the human body receives and uses the important information from the Earth's field: 7 billion crystalline magnetites in the human brain, in addition to DNA and the pineal gland are meant to receive guiding information from the band of electromagnetic frequencies that extends from the Earth's crust to the ionosphere (Schumann Resonances). Today, the Earth's field is polluted with man-made frequencies, so the human body instead receives 'junk' produced by AC electricity and wireless technology.
Variations on this specific claim are fairly ubiquitous, that our bodies' energy fields need to interact with the Schumann resonance but can't because of all the interference from modern society. It's all complete and utter nonsense. Human bodies do not have an energy field, in fact there's not even any such thing as an energy field. Fields are constructs in which some direction or intensity is measured at every point: gravity, wind, magnetism, some expression of energy. Energy is just a measurement; it doesn't exist on its own as a cloud or a field or some other entity. The notion that frequencies can interact with the body's energy field is, as the saying goes, so wrong it's not even wrong.
Another really common New Age misconception about the Schumann resonance is that it is the resonant frequency of the Earth. This is also completely wrong. Take another listen to blowing across the bottle:
Your browser does not support the audio tag.
The space inside the bottle resonates at 196 Hz, a G on the musical scale. But listen when I tap the bottle itself:
Your browser does not support the audio tag.
The resonant frequency of the glass bottle itself is about 3520 Hz, which is an A on the musical scale. Two completely different notes. That's because the bottle and the space inside are two different things, with not necessarily any relationship between them. Similarly, there's no reason to expect the Earth's electromagnetic resonant frequency to bear any similarity to the Schumann resonance. But, furthermore, the Earth probably doesn't even have a resonant electromagnetic frequency. Each of the Earth's many layers is a very poor conductor of radio; combined all together, the Earth easily absorbs just about every frequency it's exposed to. If you've ever noticed that your car radio cuts out when you drive through a tunnel, you've seen an example of this.
Now the Earth does, of course, conduct low-frequency waves of other types. Earthquakes are the prime example of this. The Earth's various layers propagate seismic waves differently, but all quite well. Seismic waves are shockwaves, a physical oscillation of the medium. Like audio waves, these are unrelated to electromagnetic radio waves. Each and every major structure within the Earth — such as a mass of rock within a continent, a particular layer of magma, etc. — does have its own resonant frequency for seismic shockwaves, but there is (definitively) no resonant electromagnetic frequency for the Earth as a whole.
So our major point today is that you should be very skeptical of any product, service, article, website, or merchant who uses the Schumann resonance, in any way, as part of a sales pitch. The Earth does not have any particular frequency. Life on Earth is neither dependent upon, nor enhanced by, any specific frequency. Most of these sales pitches are what we in the brotherhood like to call a Word Salad, sciencey-sounding language thrown together in such a way as to sound impressive to the layperson. There's plenty of sciencey goodness in understanding why and what the Schumann resonances actually are, without co-opting them to promote nonsense.
Correction: An earlier version of this incorrectly described 196 Hz as the speed at which the waves bounce back and forth between the sides of the bottle, which is wrong.
Correction: An earlier version also stated that electromagnetic waves propagate via electrons, which was an ill-conceived 'journalist's shortcut.' Electromagnetic waves do not require that electrons be present.
By Brian Dunning
Shop apparel, books, & closeouts |
Cite this article:
Dunning, B. 'Facts and Fiction of the Schumann Resonance.' Skeptoid Podcast. Skeptoid Media, 5 Mar 2013. Web. 12 Dec 2020.
References & Further Reading
Editors. 'How Radio Communication Works.' National Radio Astronomy Observatory. National Science Foundation, 17 Aug. 2008. Web. 2 Mar. 2013.
Kruszelnicki, K. 'Sceptics, energy fields and busting myths.' Dr. Karl on Triple J. ABC, 25 Nov. 2010. Web. 2 Mar. 2013.
Nickolaenko, A., Hayakawa, M. Resonances in the Earth–ionosphere cavity. Dordrecht: Kluwer Academic Publishers, 2002.
Pechony, O., Price, C. 'Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan.' Radio Science. 9 Oct. 2004, Volume 39, Number 5.
Rakov, V. Lightning: Physics and Effects. Cambridge: Cambridge University Press, 2003.
Shelikoff, M. 'Ask the Experts.' Physics and Astronomy Online. PhysLink.com, 15 Nov. 2001. Web. 2 Mar. 2013.
Copyright ©2020 Skeptoid Media, Inc. All Rights Reserved. Rights and reuse information
Frequency: 33 Hz
Note: C1 (A4 = 432/440/444 Hz)
Wavelength: 9.0846e+15 nm
Energy: 1.3648e-13 eV
Frequency: 1.618033 Hz
Notes: G#-4/Ab-4 (A4 = 432/440/444 Hz)
Wavelength: 1.8528e+17 nm
Energy: 6.6916e-15 eV
This is the last video in the Golden Ratio meditation series. The low frequencies can be difficult for some audio devices to resonate accurately. If you can't hear anything, try using headphones.
Phi is most commonly known as the Golden Ratio. It is the 21st letter of the Greek alphabet and is transliterated as 'fi'. It is a recursive geometric algorithm that appears to be the prominent mathematical ratio that is intelligently used to design many organisms. It is commonly expressed and recognized numerically as 1.618033…
Phi is everywhere, it is fundamental to nature and the development of multi-cellular organisms. Examples of Phi in nature include (but is not limited to):
– Animal life: DNA, reproductive dynamics, sensory organs, bodies and it's appendages
– Plant life: seeds, leaves, flower petals, branches, pine cones
– Cosmic systems: weather phenomena, our solar system, spiral galaxies
– Art: architecture, music, many visual works
The carrier frequencies are the sine waves used as the method to create the binaural effect. The particular frequencies used in the Golden Ratio series have been chosen for the following reasons:
– Many available audio devices can accurately resonate them
– They are comfortable to listen to for extended periods of time
– They fall within close range of other frequencies that have been used in scientific research which documented positive results
Listening to these audio files will cause your brainwaves to synchronize to the Golden Ratio, and this is the approximate center of the Delta wave spectrum.
Delta waves are the slowest of all and were originally defined as having a frequency range between 0-4 Hz. We experience these waves naturally when we are in the deepest of sleep or meditative states. These waves stimulate healing, regeneration, and healthy neuro-chemistry and as a result are vital in the maintenance of health and psychological well-being.
Delta wave activity has also been purported to aid in the formation of declarative and explicit memory formation.
Delta activity stimulates the production and release of:
– serotonin
– dopamine
– endorphins
– melatonin
– DHEA (dehydroepiandrosterone)
– GABA (gamma-aminobutyric acid)
– HGH (human growth hormone)
– PRL (prolactin)
In addition to the stimulation and production of the hormones and neurotransmitters listed above, it may reduce:
– cortisol
– anxiety
– depression
– high blood pressure
741 Hz Benefits
A plausible hypothesis would be that it is possible that the positive effects experienced from listening to this video could alter physiology, and as a result, it may have a direct effect on DNA, aging, perception, and quality of life. A more comprehensive list of potential benefits is listed below.
Potential benefits include:
528 Hz Benefits
– improved memory
– improved learning capabilities
– increased creative capabilities
– increased intelligence
– improved mental and emotional health
– improved rest and sleep
– improved focus
– improved concentration
– improved motivation
– improved confidence
– deeper meditation
– improved psycho-motor performance and mood
– reduced stress
– reduced anxiety
– dramatic personality changes
It is necessary to experience all brain wave states, and not to over-use any specific range. If brainwaves are not diversified, it could lead to adverse effects until balance has been reached.
According to a recent brainwave entrainment study by a previous president of the American Board of Anti-Aging Medicine, Dr. Vincent Giampapa, M.D.:
Electrical fluctuations in the brain were increased and as a result changed it's structure. This caused the brain to reorganize itself to function at a more complex level. New neural pathways were created, which improves the communication between different areas of the brain. These new pathways stimulate new connections, and this results in new ways to think, and new ideas. As the structure of the brain is reorganized, so is it's perception.
I would like to make sure everyone understands that this is experimental. I am not entirely certain of what the implications of synchronizing our brainwaves to the Golden Ratio could be. There are some relatively obvious conclusions that could be drawn, but in regards to an extensive scientific explanation, I cannot provide one.
33 Hz Benefits In Chinese
Headphones are definitely recommended, but not required.
Unfortunately, I couldn't fit all of my resources into this description, due to it's low character capacity.
Resources and reading material:
– https://www.ncbi.nlm.nih.gov/pubmed/17309374
– https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2044.2005.04287.x
– https://www.medicalnewstoday.com/articles/320019.php
– https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4428073/#B1
– https://www.ncbi.nlm.nih.gov/pubmed/11191043
source