It is a phenomenon characterized by the experience of seeing light without the light entering the eye.
The word phosphene comes from the Greek words fos (light) and feno (to show). Movement- or sound-induced phosphenes may be associated with optic neuritis .
Phosphenes can be induced directly by mechanical, electrical, or magnetic stimulation of the retina or visual cortex, as well as by random firing of cells in the visual system.
Phosphenes have also been reported by meditators (commonly called nimitta), people who go long periods without visual stimulation (also known as the prisoner’s cinema), or those who use psychedelic drugs.
The first account of the phosphenes is that of the Bohemian physiologist Johannes Purkinje in 1819. He was the first to publish a detailed account of the phosphenes.
In 1845, a Frenchman named Jacques Moreau was using hashish to induce a hallucinatory condition, but he was still able to report his experiences. However, such methods were not approved by his colleagues.
Eight years later, in 1853, his compatriot Brierre de Boismont declared that hallucinations were characterized by excitement and the production of images of memory and their imagination while they were in states of madness, delirium tremens, drug intoxication, nervous disorders. , nightmares, dreams.
In 1926, at the University of Chicago, Heinrich Klüver began a series of investigations. These were no different from the methods used by Moreau eighty years earlier.
The hashish had been replaced by mescaline, a hallucinogenic alkaloid derived from the peyote cactus Lophophora williamsii, and notable for the visual hallucinations it produces.
In 1928, a German neurosurgeon, Otfrid Foerster, noticed that when he electrically stimulated the surface of the occipital lobe at the back of the brain, the patient experienced the sensation of light.
However, it was Max Knoll and his colleagues at the Technische Hochschule in Munich who carried out the most extensive investigation of electrically-induced phosphenes.
The most recent research has been based on the work produced by these men, and references to their work can be found in most publications on the subject.
Phosphenes are flashes of light seen in patients with a blow to the eye, retinal traction, optic nerve compression, or optic neuritis.
More complex positive visual phenomena include palinopsia (persistence of visual images), polyopia (multiple images), micropsia (reduced images), macropsia (enlarged images), metamorphopsia (distortion of shape), and Alice in Wonderland syndrome. wonders (distortion of body image).
All of this can occur during the migraine aura. Metamorphopsia is a much more common complaint, however, among patients with macular disease. Palinopsia is more characteristically a symptom of occipitotemporal lobe damage.
The most common phosphenes are pressure phosphenes, caused by rubbing or applying pressure on or near the closed eyes. They have been known since ancient times, and described by the Greeks. The pressure mechanically stimulates the cells of the retina.
Experiences include a darkening of the visual field that moves against rubbing, a patch of diffuse color that also moves against rubbing, an ever-changing and distorting scintillating light grid with occasional dark spots (like a fly-wrinkled mosquito net) , and a sparse field of intense blue points of light.
Pressure phosphenes may persist briefly after rubbing stops and the eyes are opened, allowing the phosphenes to be seen in the visual scene. Hermann von Helmholtz and others have published drawings of their pressure phosphenes.
An example of a phosphene under pressure is demonstrated by gently pressing the side of the eye and observing a ring of colored light on the opposite side, as detailed by Isaac Newton.
Another common phosphene is “stargazing,” from a sneeze, laugh, a deep, strong cough, nose blowing, a blow to the head, or low blood pressure (such as getting up too quickly or before passing out).
These may involve some mechanical stimulation of the retina, but may also involve mechanical and metabolic stimulation (such as low oxygenation or lack of glucose) of neurons in the visual cortex or other parts of the visual system.
Less commonly, phosphenes can also be caused by some diseases of the retina and nerves, such as multiple sclerosis. The British National Formulary lists phosphenes as an occasional side effect of at least one antianginal drug.
The name “phosphene” was coined by JBH Savigny, better known as the surgeon on the ship of the French frigate Destroyed. It was first used by Serre d’Uzes to evaluate the function of the retina before cataract surgery.
Phosphenes have also been created by electrical stimulation of the brain, reported by neurologist Otfrid Foerster since 1929. Brindley and Lewin (1968) inserted an array of stimulating electrodes directly into the visual cortex of a 52-year-old blind woman, using small pulses of electricity to create phosphenes.
These phosphenes were points, dots, and bars of colorless or colored light. Brindley and Rushton (1974) used the phosphenes to create a visual prosthesis, in this case, using the phosphenes to represent the Braille spots.
In recent years, researchers have successfully developed experimental brain-computer interfaces or neuroprostheses that stimulate phosphenes to restore vision to people who are blind due to accidents.
Notable successes include human experiments by William H. Dobelle and Mark Humayun and animal research by Dick Normann.
A non-invasive technique that uses electrodes on the scalp, transcranial magnetic stimulation, has also been shown to produce phosphenes.
Human experiments have shown that when the visual cortex is stimulated above the calcarine fissure, phosphenes are produced in the lower part of the visual field, and vice versa.
Phosphenes have also been created by intense and changing magnetic fields, as with transcranial magnetic stimulation. These fields can be placed in different parts of the head to stimulate cells in different parts of the visual system.
They can also be induced by alternating currents that drive neural oscillation as with transcranial alternating current stimulation. In this case they appear in the peripheral visual field.
This claim has been disputed; the alternative hypothesis is that the current spread of the occipital electrode evokes phosphenes in the retina. The phosphenes created by magnetic fields are known as magnetophosphenes.
Astronauts exposed to radiation in space report seeing phosphenes. Phosphenes can occur as a result of some medications, such as ivabradine.
Most vision researchers believe that phosphenes result from the normal activity of the visual system after the stimulation of one of its parts by some stimulus other than light.
For example, Grüsser et al. showed that pressure in the eye results in the activation of retinal ganglion cells in a similar way to activation by light.
An old and discredited theory is that light is generated in the eye.
A version of this theory has been reactivated, except that, according to its author, ‘phosphene lights [are assumed to be] due to intrinsic perception of induced or spontaneous emission of biophotons from cells in various parts of the visual system (from the retina to the cortex).
In 1988, David Lewis-Williams and TA Dowson published a paper on phosphenes and other entoptic phenomena.
They argued, among other things, that Upper Palaeolithic non-figurative art depicts actual visions of phosphenes and neurological “shape constants,” probably enhanced by hallucinogenic drugs.
Evidence strongly suggests that phosphenes and shape constants (collectively known as entoptics) can be generated by several different methods, both intentional and unintentional. K
lüver described thirteen conditions (including taking drugs) under which entoptics could be generated. The evidence further suggests that the degree to which entoptics occur depends on the generation method used.
The most vivid images were undoubtedly generated by the use of hallucinogenic drugs. If it is true that the generation of phosphenes is not unique to humans, it can also occur in higher mammals.
If one accepts the evidence that identifies hallucinogenic drugs produce the most vivid images, our next task is to determine whether the available data supports the theory that earlier populations would have had access to hallucinogenic substances and would have been aware of their effects through the use.
It would be acceptable to suggest on the basis of the evidence that our background had phosphenes available through one form of generation or another.
It may even have happened that, with a reduction in the harshness of modern visual stimuli and a more peaceful environment, our backgrounds may have been better candidates for viewing such images than ourselves.
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As sophisticated as our brains are, they can be easily fooled. Take the vision, for example:
Our eyes gather information about the outside world and send signals to the optic nerve, which converts this information into electrical signals in a part of the brain called the visual cortex.
Our visual cortex tells us what we are seeing: a loved one, a landscape, or a computer screen. (They also flip the image up for us; our retinas see everything upside down.)
But we can easily trick our brains into thinking that we are seeing the light when our eyes are closed and we are sitting in the dark.
Every time you apply (gentle) pressure to the eyes, for example, with the palms of your hands on the closed eyelids, you tickle the optic nerve directly, and your visual cortex interprets the pressure in flashes of color against the darkness of your eyes. eyelids.
These colors are called phosphenes and are a harmless consequence of our physiology. But they could actually be useful for medical science.
Researchers from Stanford University and New York University have found a way to use phosphenes as a measure for the correct dose of brain electrical stimulation for future targeted therapies.
This type of stimulation uses small amounts of electricity applied directly to the brain.
Currently, the technique is only used to treat symptoms of uncontrollable movement in extremely ill patients with Huntington’s or Parkinson’s, but it is not sophisticated enough to treat less serious conditions.
Researchers believe it could be used to treat mental illnesses, such as depression or obsessive compulsive disorder, if they can understand exactly how neurons respond to low doses of electricity on a smaller scale.
In the new study, published Dec. 8 in the journal Neuron, Josef Parvizi, a Stanford neurologist and his colleague Jonathan Winawer, a New York University psychologist, examined the brains of four patients who underwent a checkup. seizures as part of your epilepsy treatment.
These patients already had tiny arrays of electrodes implanted into their brains to trace the origin of their seizures (asking volunteers to undergo brain surgery for a basic clinical trial, otherwise it would be too risky).
Parvizi and Winawer applied low levels of electricity directly to the patients’ visual cortices.
They tested frequencies (up to 10 times the speed of a typical resting heart rate) and amplitudes (up to 5 / 1000ths of an amplifier), separated by microseconds, up to one second at a time.
This electricity caused the patients to see floating phosphenes in their field of vision.
They asked the patients to draw the shapes they saw, and they used the drawings to trace exactly what part of the patient’s visual cortex had been stimulated through these electrical pulses.
“You can’t do this in other areas [of the brain] where you don’t have a preset map,” says Parvizi. Scientists have a pretty good map of which neurons were connected to which part of our field of vision.
This means that they could compare the phosphenes that patients saw in known neurons in the visual cortex, and pinpoint the exact range of electrical pulses in this area of the brain.
Until now, this type of electrical stimulation has been done in animals, but mice cannot tell us exactly what kind of pattern they see or feel.
And while doctors can use electricity in the brain to treat patients with advanced movement disorders, scientists have not been sure how this type of electrical stimulation would work more superficially on a different set of neurons with and with greater precision.
In this case, the researchers found that higher loading led to larger phosphenes, but only up to a point: After a certain point, the subjects did not report larger phosphenes, but colors with a brighter intensity.
It is still too early to see many clinical applications with direct electrical stimulation in the brain; This study only involved four people, and it would have to be replicated much more widely first.
But Parvizi hopes this dose can be applied to future therapies for conditions that originate in the brain, such as depression and obsessive compulsive disorder.
The appearance of phosphenes
The appearance of phosphenes can be spontaneous and can be provoked in various ways. They appear spontaneously only when visual stimuli are lacking and especially when the viewer is subjected to prolonged visual deprivation.
Phosphenes can explain “illuminations,” visions, or the experience of “seeing the light” reported by religious mystics meditating in the dark; they are the ‘prisoner cinema’ experienced by people in dark dungeons; they may well cause ghost and ghost reports.
Darkness is not a requirement; only the absence of external visual stimuli is needed. Phosphenes are a hazard to the long-distance truck driver who watches for hours in a snowstorm.
Airplane pilots often experience phosphenes, especially when flying alone at high altitudes, where the sky is clear and void of the usual depth signals.
To exclude any optical entry, enter a totally dark room or wear a light-tight bandage. However, once this is done, visual perception does not end.
There is no impression of total blackness. Once the eye has adjusted to the dark, and especially if one relaxes, the visual field brightens: wispy clouds and moving specks of light appear, usually in pastel shades of blue, green, orange and yellow.
If one presses the eyes more, the figures are evoked. These subjective images resulting from the self-illumination, so to speak, of the visual sense are called phosphenes.
Because phosphenes originate within the eye and brain, they are a perceptual phenomenon common to all humanity (past and present, it is assumed), and they are extremely interesting from a psychological and aesthetic point of view.
Because their patterns must be closely related to the geometry of the eye, the visual cortex provides a means of studying the exquisite functional organization of the brain.
It is instructive for an adult to ask an articulate child what they see when they close their eyes at bedtime. Children have an ability, which diminishes with adolescence, to evoke phosphenes quite easily.
Phosphenes may in fact be an important part of the child’s real environment, as he / she may not easily distinguish this internal phenomenon from those of the external world.
To “see stars” is to see phosphenes, an experience that can be induced by a blow to the head or by other mechanical means. A less violent procedure is to apply pressure to the eyeballs with your fingers.
If, with the eyes closed, one gently touches the lid with the tip of a finger, a phosphene appears: a bright circle or part of a circle, apparently about a quarter of an inch in diameter.
The location of the phosphene in the visual field is opposite to where the finger touches: at the outer edge of the field when the eyelid is touched near the nose, it goes down in the field when the center of the upper eyelid is touched.
Increased pressure on the eyeball produces more dramatic phosphenes. One procedure is to apply the index fingers to the inner edge of the eyeballs and press inward and toward the temples.
The field of view lights up, and then as pressure is held for a few seconds, a sparkling pattern appears – a kind of chessboard or shifting field of bright dots, sometimes with complex substructures arranged around a luminous center.
When the pressure is released, the chessboard fades, sometimes leaving the central luminosity behind. If the pressure is renewed, a pattern of bright, irregular lines appears that resembles a system of blood vessels.
When the pressure is released again, a fine watermark image appears and remains for some time. The checkerboard layout is probably a manifestation of the order of the retina’s neural network; it moves in the visual field as the gaze moves.
The watermark, on the other hand, can be generated further along the visual path, as it remains stationary no matter where you look at it.
However, there is a degree of individual sensitivity; some people can cause phosphenes to occur regularly with little provocation and after pictures that last a long time, others not
It is in this next section that we must consider the other methods of generating phosphenes, namely the taking of hallucinogenic drugs to induce altered states of consciousness.
Not only the human element is susceptible to hallucinations, but the entire population of mammals. “Unreal” visual perceptions would have been experienced long before the Upper Palaeolithic.
It has been widely accepted that the human nervous system is universal and that it is very similar now as it was in the Upper Palaeolithic.
Hallucinations are thought to have a cultural bias in their generation. It should follow that any description of a hallucination will also be culturally biased.
This being the case, the emphasis has been transferred to the images that are generated in the nervous system. These phosphenes and shape constants are believed to be culturally unbiased during their generation.
However, they can be culturally impartial during altered states of consciousness, but, as with hallucinations, any explanation or description of them becomes culturally biased.
The viewer makes a conscious decision as to which images to pay attention to: he uses subjective terminology in the description of his visions and cannot avoid the innate urge to use similes.
Because these form constants and phosphenes are derived from the human nervous system, all people with altered states of consciousness, regardless of their cultural background, are susceptible to perceiving them.
Phosphenes can be induced by physical stimulation, such as pressure on the eyeball, and are therefore entophthalmic (“inside the eye”). The shape constants are derived from the optical system probably beyond the eye.
Form constants and entoptic phenomena are largely geometric shapes and phosphenes or entoptics are not culturally biased. Hallucinations are more complex, culturally controlled iconic visions.
Most of the drugs that give rise to these images are called hallucinogens, but he goes on to say that other drugs and substances can produce similar effects.
Therefore, it is claimed that most psychoactive compounds (to the extent that they cause the mind or attention to wander) can also be considered hallucinogenic.
These can include: alcohol, carbon dioxide, cocaine, cortisol, digitalis, scopolamine, and even high-nicotine tobacco.