Level: expert ·Topic: neurobiology of synaesthesia, cognitive advantages, genetics of perception
For most people, the letter 'A' is just a sign.ForWassilyKandinsky it was yellow.ForVladimirNabokov it was a 'faded flannel' — his exact description in his autobiographySpeak,Memory.Nabokov described his synaesthesia in detail — and noted with mild irritation that his mother and his sonDmitri had it too, but with different colours.Synaesthesia runs in families.This is not a metaphor.
Part 1.WhatSynaesthesiaIs andHowItWorks
Synaesthesia is a neurological phenomenon in which stimulation of one sense automatically and involuntarily triggers perception in another.It is not imagination and not metaphor: the synaesthete's brain literally generates a sensory experience that has no source in the external environment.
The most common forms:
- Grapheme → colour: letters and digits are perceived as coloured.The most studied and widespread form (~65% of all synaesthetes).
- Chromaesthesia (sound → colour): sounds trigger visual impressions — colours, shapes.Characteristic of many musicians:FranzLiszt,NikolaiRimsky-Korsakov,OlivierMessiaen.
- Time → space: days of the week, months, years are arranged spatially around the person. 'Monday is to my left,Friday to the right and slightly higher.'
- Lexical-gustatory: words evoke taste sensations.Rare but well documented.
- Mirror-touch: watching someone touch another person, the synaesthete feels the touch on their own body.
Part 2.TheNeurobiology:WhatHappens in theSynaesthete'sBrain
Two main competing hypotheses explain the mechanism of synaesthesia:
- The 'structural connections' hypothesis (Ramachandran &Hubbard): synaesthetes have additional anatomical connections between adjacent cortical regions.For example, the grapheme-processing region (angular gyrus) sits close to the colour-processing area (V4).A small 'crossing' of axons between these regions — and a letter 'triggers' a colour.
- The 'disinhibition' hypothesis (Cytowic &Eagleman): in all people, hidden cross-modal connections between sensory regions exist but are normally suppressed.In synaesthetes, this inhibition is less effective — the connections are 'disinhibited.'
fMRI studies support both hypotheses to varying degrees.Most convincingly: in synaesthetes, processing a 'stimulus' (for example, a letter) genuinely activates the region for processing the 'inductor' (colour).This is not imagination: the activation is real and reproducible.
Part 3.TheGenetics ofSynaesthesia
The familial inheritance of synaesthesia is well documented.Nabokov is not an exception.Several families with synaesthesia have documented transmission across multiple generations.The inheritance pattern is autosomal dominant with incomplete penetrance and variable expressivity: if you have synaesthesia, there is roughly a 50% chance of passing the predisposition to your children — but their specific form may be different.
Genomic research into synaesthesia:
- 2018 study (Tilot et al.,PNAS): whole-exome sequencing of three families with synaesthesia.Rare variants were found in genes associated with axon development and interneuronal connection formation —ROBO3,COL4A1, and several others.The common theme: genes controlling neural 'wiring' during early development.
- Associations with the serotonin system: several studies have found a link between synaesthesia and variants of serotonin receptor genes (HTR2A).This is consistent with the observation that hallucinogens acting on 5-HT2A receptors produce temporary synaesthesia in non-synaesthetes.
Part 4.TheCognitiveAdvantages ofSynaesthetes
Why is synaesthesia so much more common among artists and scientists?The data point to several real cognitive advantages:
- Memory: synaesthetes show better retention of words, numbers, and sequences — through the additional sensory 'anchor.'A shopping list in which every word has a colour is easier to remember.
- Creative thinking: the ability to connect the unconnected — metaphorical thinking — is at the heart of creativity.Synaesthesia may be the neural substrate of this capacity: a brain accustomed to cross-modal connections finds non-obvious associations more readily.
- Musicality: chromaesthetes (sound → colour) frequently possess absolute pitch.The additional 'colour marker' for each note may help identify it without an external reference.
- Mathematical intuition: synaesthetes for whom numbers are arranged in space (number-form synaesthesia) often navigate large numbers and patterns more naturally.
Part 5.FamousSynaesthetes:ABriefRegister
- VladimirNabokov: grapheme → colour. 'A' — faded flannel, 'V' — a clear warm pink.
- WassilyKandinsky: sound → colour.His painting directly reflected his attempt to 'write' sound in pigment. 'Blue is typically a heavenly colour.It deepens into infinity' — and this was not a metaphor, but literal perception.
- NikolaiRimsky-Korsakov: keys had colours.C major was white,D major yellow.He debated withAlexanderScriabin about whetherScriabin's colours were 'correct.'
- Phoenix (ThomasMars): the frontman ofPhoenix has spoken about chromaesthesia.The albumWolfgangAmadeusPhoenix was developed with specific sound 'colours' as a guiding principle.
- NikolaTesla: according to some accounts, he had pronounced synaesthesia — words triggered taste and tactile sensations.This is based on his own descriptions rather than clinical documentation.
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