Color mood


What is synesthesia and how does it occur?

Smell sound, see color words. We think this is incredible, but it is commonplace for people endowed with the ability to synesthesia. Thousands of people are living with this stunning feature, but its neurobiological basis is still controversial.

…my mother all this seemed quite natural, when my property was discovered for the first time: I was six or seven years, I built a castle out of colorful alphabet blocks — and casually remarked to her that they are painted incorrectly. We immediately found out that my letters are not always of the same color that it…

These autobiographical lines belong to Vladimir Nabokov, one of the most famous synesthetes. The perception of the individual letters for it was extended, affecting several different senses.

Moreover, the master saw the colors of the letters, he says, he is feeling them, experiencing the texture and taste of the sounds:

What is synesthesia and how does it occur?

Smell sound, see color words. We think this is incredible, but it is commonplace for people endowed with the ability to synesthesia. Thousands of people are living with this stunning feature, but its neurobiological basis is still controversial.

…my mother all this seemed quite natural, when my property was discovered for the first time: I was six or seven years, I built a castle out of colorful alphabet blocks — and casually remarked to her that they are painted incorrectly. We immediately found out that my letters are not always of the same color that it…

These autobiographical lines belong to Vladimir Nabokov, one of the most famous synesthetes. The perception of the individual letters for it was extended, affecting several different senses.

Moreover, the master saw the colors of the letters, he says, he is feeling them, experiencing the texture and taste of the sounds:

I do not know, however, whether there to talk about “rumor”: color sensation is created, in my opinion, tactile, lip, almost by taste. To thoroughly determine the color of the letters, I have the letter prosmakovat, give it to swell or emit in your mouth, while imagining its visual pattern“.

Despite the exclusivity of their literary gift in his synesthesia, Nabokov was not alone. For the first time this phenomenon is described by another bright scholar-encyclopedist and, incidentally, a cousin of Darwin, Francis Galton. When this mysterious peculiarities of perception of irritation of one organ of sense is not only sensations, characteristic for him, but some sort of parallel feeling. As a result, the objects and phenomena acquire unusual qualities: the sound of music, numbers, letters and even whole words get the color, smell and even taste.

I must say that synesthesia is a pretty complex subject to study. Definitely hard to processeditorevent its types and to determine their prevalence. Too brightly it is manifested.

60 shades of reality

For more than two centuries of research on the phenomenon has been described for about 60 variants of synesthesia. However, they occur not in equal proportions.

The undisputed leader in frequency — grapheme-color synesthesia, when the perception of letters or numbers are supplemented by the sensation of color. It has approximately 45% of the total number of synesthetes. Not much less, apparently, common chromesthesia, as a result of which the sound is coloured by the perception of color. As awful popular spatial-numeric synesthesia, when the numbers and especially the date is a certain place in the perceived space synesthete.

But apparently feelings can interfere in almost any combination, though it occurs slightly less often. Numbers and shapes, sounds and tactile sensations, even the tastes can blend in a whimsical ornament of sensuality. Not so rare are cases when several mixed feelings. And the legendary mnemonist Solomon Shereshevsky, apparently, had synesthesia, generally affecting all five senses.

So in fact divided by the types of synesthesia is not so easy. It is even more difficult to determine its prevalence. But we can say that various forms of synesthetic perception suffers from a few tenths to a few percent of the human population evaluation of the frequency of the dizzying vary from easy to take fantastic 1/2000 to 1/200 and even 1/100. Frankly, personal experience is hard to accept the second assessment — too many synesthetes wandering around! But, if you go into the details of the research, everything falls into place.

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Often synesthesia is still divided into two types — projective and associative. Projection synesthet really see the colour of sound or the black letters of the alphabet. It is a feeling just as real as the color of the traffic light for us. But associative synesthet nothing watching. He only associates a letter with this color. It seems that the difference is small, but these two groups are completely different Stroop test.

Scheme: Anatoly Lapushka / Chrdk.

During the test the participants put a deck of cards with color names. But these names are written in a colored font that does not match the name of the color on the card. The researcher ruthlessly requires the subject to name the color of the font with the maximum speed. The man who does not understand the meanings of words, will cope with the task as quickly as if it had been the usual coloured cards. But if the subject understands the signature, it will show a noticeable delay in the responses. This reaction is involuntary, and it is almost impossible to disguise. Therefore, according to popular history, in the 50-ies of the Stroop test were actively used by the CIA to identify potential Soviet agents, hidden knowledge of the Russian language.

In experiments, synesthetes had to walk in the footsteps of the elusive Soviet spies. They tested an alternative version of the Stroop test: instead of color names on the cards were colored letters. It turned out that looking at a color alphabet, a synesthete-projectionsto honestly see their individual “right” (according to Nabokov) the color of the letters and make distinct an effort in order to call it objective painting, showing a delay in the response. Association the first. They quickly referred to the objective color letters long and thinking about a colour Association. Scientists, who gave a low evaluation frequency, in most cases spoke only about the projection synesthetes, and their colleagues, have received large numbers involved there and the associative synesthetes.

Illustration: Sergey Kozlov / Chrdk.

However, despite all the difficulties with the classification of the known shades of synesthesia, common sense and even a cursory knowledge in neurobiology suggest that such diverse forms of synesthesia have similar mechanisms of development. In this area scientists already have something to share with us.

Unnecessary communication

The most popular concept of the emergence of synesthesia known as the cross-activation theory. One of its authors — world-renowned neuroscientist and popularizer of science, Vilayanur Ramachandran. (By the way, the reader has the rare opportunity to learn more about this concept right out of his book, translated into Russian language.)

The basic idea behind this concept is simple: nerve centers that process information of one sense organ, sometimes form a connection with the brain areas responsible for different feeling. It turns out that in addition to the canonical associative areas stimulus activates another and related areas, causing an additional sense. For example, when grapheme-color synesthesia should appear cross-links between the area of the brain that recognizes the image, and the area responsible for color detection.

Scheme: Anatoly Lapushka / Chrdk.

At first glance it seems that the theory of cross-activation is contrary to the fact that the level of synesthetic perception in “Grafenau” is very different. Some of them respond colour feeling only Arabic number, while the Roman version of their synesthesia ignores. That is, these people color is not associated with the number and with very specific graphic symbol. Sensations of other synesthetes, on the contrary, obediently turn when looking both Arabic and Roman numerals option, which means that their brain perceives color the very idea of numbers.

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Also described cases when not in regular numerical sequence, but only a series of dates, days and months are perceived “color”. The cross-activation theory explains the diversity of manifestations of synesthesia the fact that the crossing signal paths of different synesthetes occurs at different levels. Someone it affects only the sensory zone are able to perceive signs of specific alphabet and numbers same font styles, and some people have this cross-over is much higher in the hierarchy of the zones of the cortex — centres that operate on numbers or dates.

This idea is consistent good comparison of synesthetes and relatives. Synesthesia suspiciously often passed down from generation to generation. A 2007 study showed that of the 53 studied synesthetes 42% had a family of synesthetes among first order relatives (parents/children). However, the severity and nature of symptoms, even in the family, as a rule, is very different.

Heavy legacy

The search for genetic determinants of synesthesia — a very long detective story filled with intrigue and exciting twists. Back in the mid 90s in the analysis sample of synesthetes (by the way, it was small — just 28 people) was that the ratio of men and women in it — 1:6. Reflecting on this strange gender injustice, the authors thoroughly dug into the ancestry of the test subjects.

What they learned led them to the suggestion that synesthesia may be determined by a single dominant gene located on the sex X chromosome, and a huge gender imbalance to explain its potential lethality for males. Without going into the possible mechanisms of this, is to say that cases like slightly exotic inheritance are known, so the idea seemed quite realistic.

However, more recent work has allowed us to exhale a worried his fate men synesthetes. They are not so rare and miraculously surviving an exception to the rule: the larger the sample, the gender disparity decreased to a moderate 2:1 in favor of women, which was rejected the assumption of high mortality of a hypothetical X-linked gene for men. Instead, the authors suggested that the proud (or shy) holders karyotype 46 XY rarely responded to ads researchers about finding subjects, preferring to keep their synesthesia to yourself.

And finally, in a very recent article, the researchers stated that they found a whole bunch of candidate genes for the title of the synesthesia gene. Modern technologies of DNA sequencing miracles: the genetic analysis of the 43 families of synesthetes has been read more than a hundred exomes (sets of genome sequence from which the RNA is read). Their analysis allowed us to identify 37 genes, some of which correlate with the color-sound synesthesia. The best hope has raised six of them — those associated with the process axonogenesis in the visual and auditory areas of the cerebral cortex.

Axonogenesis is a process occurring during the formation of the brain, during which immature neurons form spines-axons. Engage different signaling substances, axons sprout in other areas of the brain, tying them together. Most likely, the rare variants mentioned above genes characteristic of synesthetes, increase axonogenesis between visual and auditory cortex. In the end, the signals from the auditory cortex cross-activate the visual cortex, creating visual sensations.

We can say that the idea of the only X-linked allele synesthesia failed, but the concept of cross-activation has found great confirmation from molecular genetics. However, we should not think that the situation with the mechanism of synesthesia is clear. To understand how we are all far from understanding this phenomenon, let’s look at the alternative concepts are also not devoid of convincing evidence.

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Alternative to the cross-activation theory of disinhibition of feedback. Through it, higher associative centers are associated with a variety of sensory centers two-way communication. In turn, the touch regions were also cross-linked. However, all the intricacies of selling and cross-links in normal and retarded are not capable of conducting signals when the stimulation was active only channel uplink from sensory areas to the associative. It provides one or the other experience of the world.

Synesthetes for some reason, reverse and crosstalk rastormazivate, causing the spread of excitation in the parallel sensory and associative areas. It turns out that from birth synesthet may not possess the more related areas of the cortex: just the links that everyone has a brain, but suppressed, he somehow active and transfer the signal from one brain to another.

If you follow this idea, it turns out that the brain has everything necessary for synesthetic perception neural connections! Is it possible to stir and become synesthet? Judging from everything, is possible. A similar effect is achieved by the use of certain psychedelics.

Synesthesia hour

The use of certain drugs, mainly tryptamine-hallucinogens like LSD, similar in structure to the neurotransmitter serotonin, causes sinestesi-like feeling. Considering that the substances are mainly known as hallucinogens, one would expect that their effects would relate to visual images. But it turns out that even the blind from birth people do not have idea about visual images, LSD causes synesthetic experiences.

A curious case is described in an entirely fresh publication. Born premature, the patient soon after birth was the victim of retinopathy of prematurity, sadly common in the 40-ies due to excess concentration of oxygen in incubators. Complete blindness did not prevent him from music, and he soon began to live life badass rock musician with all the ensuing consequences. According to the testimony of the blind rock-star experience of taking LSD in particular stood out from his experiments, giving rapid synesthetic experiences. The third Brandenburg Concerto of Bach in the background of LSD created a blind musician tactile immersion “in the most wonderful light at the waterfall.”

Illustration: Sergey Kozlov / Chrdk.

However, it appears that between innate and pharmaceutically-induced synesthesia are much more differences than similarities. Yes, these two phenomenon are very similar, but they are clearly not the same. In these two forms of synesthesia are activated different areas of the brain that is seen on fMRI. Induced synesthesia is accompanied by changes in perception, and her character is not constant, as in the case of congenital synesthesia, and depends on the current state of experimental and experiences prior to the study.

When a scientist with a run thrown into the study of some ugly another mysterious natural phenomenon, the first question he asks is the question “how?”. I must say that after two centuries of study of synaesthesia today, we are still very far from a satisfactory explanation of its mechanisms. However, when it comes to biological objects, familiar with the concept of evolution, from curious explorers always remains in reserve of the second, well, a very important question — “why?”.

And in answer to it, in terms of synesthesia, we have advanced much further. Synesthesia can be very useful to its owners. Moreover, what we call synesthesia, only taken to extremes a property inherent in all representatives of our species, and it gave us a fair start in the struggle for survival and allowed us becoming who we are now. But more about this we will talk next time.

To be continued.

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