It appears that synesthesia is the basis of our experience of the world, though to different degrees in different individuals. People with synesthesia experience an overlap of the senses, where something like sound can bring up representations of some object or color. As an example, the letter ‘A’ may conjure up the color red. This synesthetic process actually seems to be what normally underlies our perception of language. For example, when I say the word ‘dog’, it elicits imagery of some creature, the letter combination made up of visual symbols (d, o, g), and even the sound of the word. Here we will explore the connection between synesthesia, learning, savantism, and childhood.
This ‘dog’ type of synesthesia seems to be maintained in almost everyone because it is useful to us and we are trained to maintain it. Since society does not define an association between the letter A and the color red as a meaningful associative pattern of sound-symbol-color, most people may drop such associations in favor of holding onto only those associations that society has determined as meaningful. The word ‘dog’ does not necessarily have any inherent or natural meaning, but we have associated such a sound with the dog creature and society has mandated that we maintain such associations. Meanwhile the ‘red-A’ association is not talked about by society much at all, so it will be rare for people to maintain these associations, at least for most individuals. The synesthetic connections that are not used past childhood may become pruned away. There is also evidence that those with synesthesia have increased white matter tracts connecting parts of the brain (Whitaker et al 2014; Zamm et al 2013), which may be these unpruned connections.
When we are children, we have more synapses and connections in the brain, but we eventually grow and begin to prune away these connections in what is termed synaptic pruning. This is important for narrowing down connections and removing associations like ‘red-A’ so that we have a more narrow and refined perception of the world. Much of the more drastic synesthetic sensations are likely pruned away during infancy (Wagner & Dobkins 2011). Though, synaptic pruning continues throughout life, with major periods occurring during youth and adolescence (Spear 2013; Chechik, Meilijson, & Ruppin 1999).
Interestingly, psychedelic drugs induce synaptogenesis (Ly et al 2018), which is arguably the opposite of synaptic pruning. It is the growth of synapses. Psychedelics are also widely known to induce synesthesia temporarily. We might expect that children are constantly having synesthetic and even psychedelic type experiences before synaptic pruning takes over. I’ve argued this in The Phoenix Effect hypothesis in much more detail. The next section covers the update!
It is important to consider that animals of all kinds likely experience synesthesia as well. When an animal hears the sound of water and conjures the associated concept of water in their mind, I feel that this too is a kind of synesthesia. It seems that synesthesia is the very basis of our integrated perceptions of the world. For children they may scan the near-infinite associative cross-sensory patterns and learn how to reduce awareness to only the meaningful patterns.
The Phoenix Effect
Update from The Phoenix Effect:
Like with psychedelics and infants, enhanced structural (infants) and functional connectivity (infants and psychedelics) of the brain is observed in synesthetes (Sinke et al 2012; Rouw & Scholte 2007; Zamm et al 2013). It could be that psychedelics induce synesthesia through synaptogenesis or another related mechanism.
There is also an argument that serotonin hyperactivity during development may bring on synesthesia (Brogaard 2013). Normally, synaptogenesis may reduce as we age out of infanthood, but in the synesthetes, perhaps high serotonin activity causes synaptogenesis to remain intact for longer, thus slowing the synaptic pruning process that normally eliminates synesthetic experiences. A recent book from 2020 actually argues that all children are synesthetes at first, until we lose this ability (Ward & Simner 2020).
From that chapter:
The most influential neurodevelopmental account of synesthesia is the Neonatal Synesthesia Hypothesis (or Infantile Synesthesia Hypothesis) originally put forward by Daphne Maurer and colleagues. Put simply, the idea behind the theory is that all human infants are synesthetes and most people lose this ability during development (becoming adult nonsynesthetes) but a few retain this ability (becoming adult synesthetes). The evidence for the theory comes from several different observations:
1) Increased connectivity during infancy. Synaptic density is greatest soon after birth with synaptic density in sensory cortical regions decreasing toward adult levels earlier than in other regions. Glucose metabolism, a sign of functional synaptic activity (rather than amount of synapses), also shows an early peak and fall. In particular, there is anatomical evidence of pathways from auditory to visual cortex that are normally reduced or removed during development.
2) Less domain specificity during infancy. Cortical regions are far less specialized during infancy and, in particular, may respond more strongly to multiple sensory modalities relative to older children or adults. For example, regions normally specialized for spoken language respond more strongly to visual inputs early in life.
3) Presence of synesthetic-like correspondences in early life. For example, 3- to 4-month-old infants will orient toward high and pointed shapes when played a high-pitched tone and will orient toward low and rounded shapes when played a low-pitched tone. This has been taken as evidence that these correspondences are innate rather than learned.
This notion of a lost synesthesia from childhood also resonates with the points made about lost eidetic memory and phonetic sensitivity. Perhaps synesthesia is an multisensory exploratory mode that exists predominantly in children. Those who undergo less synaptic pruning may maintain some of this synesthesia. Then as we learn which associative sensations are most useful and relevant to our lives, we begin to disconnect the connections that our brain has decided are irrelevant and non-useful to us. This could be understood as a multi-sensory calibration process.
The function of this synesthesia may be very general to learning and perhaps especially language learning. While the association of the letter ‘A’ and the color red might seem erroneous, the association of the word ‘red’ and the color red is considered a correct association in the English language at least. Synesthesia may be somewhat uncommon partly due to the fact that it is essentially defined as having multisensory associations that we normally do not. We do not culturally entrain the population to learn an association like red-A, but we do entrain one for the word and color red. Uncommon associations are merely the ones people have learned on their own, without society’s cultural entrainment. Language may be synesthetic.
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Savantism and Synesthesia
An interesting blog post on Nature noted that synesthesia could be implicated in some cases of savantism. In savantism, individuals are gifted with some amazing cognitive ability, often one that is very particular and also often at the cost of some other ability. Usually it is something like extreme photographic (eidetic) memory. Sometimes it is extreme music capabilities. The costs are often social or other forms of learning impairments. Synesthesia is more common in autism (Baron-Cohen et al 2013), which is also commonly associated to savantism.
The Nature post describes the case of Daniel Tammet, an individual with autism and synesthesia, who was able to memorize and recite 22,514 digits of the number pi. The description Daniel gave for his subjective experience of synesthetic math is quite psychedelic.
Quoted from the Nature post:
In an interview he gave with The Guardian, Daniel explained, “When I multiply numbers together, I see two shapes. The image starts to change and evolve, and a third shape emerges. That’s the answer. It’s mental imagery. It’s like maths without having to think.”
In regards to the autism connection, the paper by Brogaard mentioned earlier argues that synesthesia my be associated to autism due to differences to the serotonergic system in early development (Brogaard 2013).
Most fascinatingly, a study found that adults can be trained to become synesthetes. Not only this, but doing so seemed to improve IQ (Bor et al 2014). On the repeat administration of the IQ test, the participants who were trained to be synesthetes saw an increase in IQ of 12.46 points, while the control subjects only saw minor or basically no improvement. This study was small, so more research would be needed, but it is quite an interesting find.
Besides this, psychedelics have been observed to increase learning and memory, though these effects seem mixed. These effects are likely dose-dependent as well. DMT was found to enhance learning, memory and neurogenesis in a new study (Morales-Garcia et al 2020). One study found that psilocin impaired acquisition in rats and the high dose even impaired retrieval (Rambousek, Palenicek, Vales, & Stuchlik 2014). Another study on psilocybin observed enhanced fear extinction learning that was dose-dependent, occurring more at the lower doses (Catlow, Song, Paredes et al 2013). MDMA enhanced associative and non-associative learning in rabbits (Romano & Harvey, 1994). MDMA was found to enhance plasticity with repeated neurotoxic doses in rats (Morini, Mlinar, Baccini, & Corradetti 2011). MDMA also enhanced fear extinction learning, which is relevant for PTSD (Young, Andero, Ressler, & Howell 2015). LSD was found to enhance associative learning in rabbits (Gimpl, Gormezano, & Harvey 1979) and intrahippocampal LSD was found to accelerate learning in rabbits (Romano, Quinn, Li et al 2010).
Another study found that repeated LSD dosing restored impairments to learning in ‘depressed’ rats (Buchborn, Schröder, Höllt, & Grecksch 2014). A recreational dose of LSD (100ug) revealed cognitive impairments in humans, including deficits to executive function, working memory, and mental flexibility (Pokorny, Duerler, Seifritzet al 2019). Another study claims that cognitive flexibility is increased after the acute dose of LSD (Carhart-Harris, Kaelen, Bolstridge et al 2016).
Dosing LSD in rats was found to accelerate reversal learning, which involves making a choice in a decision making task after learning to make the opposite choice (King, Martin, & Melville 1974). Psychedelics may be able to stimulate cognitive change this way. This seems to be paradoxical to the ‘decreased flexibility’ observed in the other study on LSD. The reversal of learning discussed in the next section is not necessarily reversal learning, but it could be related. Below the described effect is a biological ‘reversal of learning’.
Clearly the effect of these mechanisms on learning is complex. Not to mention, these drugs have multiple mechanisms, which may even oppose one another. One might wonder if the mixed effects observe could also connect to this puzzle of savantism, where enhancements and impairments seem to coexist.
Music Is Synesthetic
Another obvious form of synesthesia that most people have is with music. Music often elicits emotional responses, which are arguably a different kind of interoceptive sense. So in this sense, the synesthesia is temporal-auditory patterns and emotional experiences. I feel that these emotional responses that music elicits may actually be evolved as responses that are intended to originate from vocalizations. There are certain sad sounds a person can make, often times a vocal de-scension. There are also certain kinds of sounds we make with other various emotions. While we speak, we may use these kinds of changes in relative pitch to communicate our tone and mood, and music may exploit some of the patterns of relative pitch to create melodies.
Something else that connects here is the “speech-to-music” illusion. This illusion involves the repetition of speech in a loop, which begins to sound like a melody after some period of time. It is well-known that music involves the repetition of auditory patterns, but why might this become ‘musical’? To me, it seems that repetition may enhance the awareness of nuances and temporal relativity of auditory patterns, thus allowing our brain to better notice the distinct relative pitch changes and essentially a kind of temporal and pitch based geometry. Without the repetition, our brain may not be able to easily track the nuances as the complexity gets too high. When complexity goes exceedingly high, we may experience something akin to ‘white noise’ in which the auditory signal is too chaotic to comprehend meaningfully.
Some of those ideas were explored in the recent article, Musicalization.
Do you remember being psychedelic during childhood? I am very curious about this, so if you remember having memories from very early childhood, please comment about the story below in the comments!
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Citations
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