Synesthesia can be induced by the intake of certain drugs or by the use of narcotic substances (eg mescaline or LSD), by sensory deprivation or by some brain lesions. These perceptual "interferences" can also occur involuntarily and spontaneously in subjects who have greater communication between the regions of the brain responsible for processing the information arriving from the various sense organs.
Synesthesia can manifest itself in different forms: words can have color, sounds can have smells, numbers can have tastes, and so on.
.Synesthesia affects a small segment of the population (indicatively it occurs between 0.05% and 4% of people).
Curiosity: synaesthesia and creativity
Throughout history, many artists, writers and poets have experienced the phenomenon of synaesthesia: for example, the Russian painter Kandinsky hoped that his paintings could be heard, as for him the colors became a "choir" on the canvas. .
The poet Baudelaire, on the other hand, composed the famous "sonnet of vowels" under the effect of sensory distortions, probably induced by the use of drugs.
(less used) that occurs during brain development.
Some forms of synaesthesia (especially in the grapheme-color type), on the other hand, could contribute to childhood memories (note: the condition was found in people who played with colored magnetic letters as children). In the latter case, synaesthetes seem to simply evoke memories and mental associations.
The use of hallucinogenic drugs (such as LSD, mescaline and, in some cases, marijuana) or antidepressants (especially selective serotonin reuptake inhibitors) can cause the onset of synaesthesia, mostly temporary.
The phenomenon can also occur in response to brain damage (eg stroke), experiences of sensory deprivation and lesions of peripheral nerve structures (such as limb amputation).
However, in about 4% of people, the phenomenon occurs in normal conditions, appearing spontaneously, involuntarily and stable over time.
Synesthesia can also be induced under normal conditions, through hypnosis and meditation.
Experiences of a synaesthetic type can also result by modifying the excitability of specific areas of the cerebral cortex (for example, as a consequence of diseases). If it results from a neurological disorder, in fact, synaesthesia can derive from the perception of a stimulation in an area far from point where this is exercised.
Among the so-called acquired forms, synaesthesia can occur in the context of brain tumors, stroke, temporal lobe epilepsy and head injury. In some cases, the phenomenon can be found in association with dyslexia, attention deficit and, rarely, autism.
Predisposing factors
People predisposed to experiencing synaesthesia tend to be:
- Members of the same family: synaesthesia can be inherited as a hereditary genetic component and can be found mainly within the same family (one third of synaesthetic subjects have a close relative who has the same condition). The trait responsible for synaesthesia is found on the X chromosome.
- Neurologically normal: people with synaesthesia have normal intelligence and standard neurological tests do not show any alterations, even if they often display excellent memory skills and strong creative abilities.
- Left-handed people: synaesthesia is more likely to occur in left-handed people or in conjunction with other conditions such as allochiria (confusion of the right hand with the left) and a poor sense of orientation.
- Female gender: Synesthesia is found more commonly in women than in men. The reason for this difference is not yet known.
- Synesthesia can involve any sense.
The most common form of synaesthesia occurs when someone associates a certain color with a specific letter of the alphabet or a number, the days of the week with particular geometric shapes, the words written in a book with a specific smell or taste. For example , a synaesthete (that is, a person with synaesthesia) may see the mint green word "piano" or the number "4" as dark brown. In other cases, people experience synaesthesia by perceiving sounds in response to a specific smell or they see something in reaction to a tactile stimulus.
- Synesthetic experiences can occur in any combination and number of senses or cognitive pathways.
Synesthesia can manifest itself in various forms, as it involves the involvement of different regions of the human brain.
If only the five basic senses are considered (sight, smell, sound, taste and touch), about twenty different types of synaesthesia are already obtained: a synaesthetic perception can result from the combination of hearing-smell, taste-vision, etc. For example, a note or a word can evoke a color, the sight of a dish makes you perceive its flavor, touching some materials can trigger a particular taste or emotion or a perfume brings to mind specific images.
In reality, there are a greater number of possible combinations: although it is extremely rare, in fact, in some people, synaesthesia can involve three or more senses at the same time.
- Synaesthetic perceptions are specific to each person.
Several people with synaesthesia almost always disagree about their perceptions. In other words, if one synaesthete thinks the letter "q" is blue, another might see it as orange.
when listening to a Beethoven violin concerto, the synaesthete must always perceive this taste when hearing the melody). However, perceptual synaesthesia is unidirectional, so if a musical note is perceived as a color, it cannot be taken for granted that by seeing that key the mind will evoke that particular note.Furthermore, the perception must be generic: colors, lines or shapes can be perceived in response to a certain smell, but the synaesthete cannot see something as complex as a room with people, furniture and paintings on the walls.
- Memorable: Often, secondary synaesthetic perception is remembered better than primary perception; for example, a synaesthete who always correlates the color purple with the name of "Laura" often remembers that a woman's name is purple, rather than associating, in particular, the word "Laura".
- Emotional: synaesthetic perceptions can cause the person experiencing them emotional reactions, such as pleasure or unpleasant sensations. Most synaesthetes report, however, that their experiences are neutral or associated with a number of benefits (such as creativity).
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