Inducing Synesthesia
An interesting way to optimize your brain.
TL;DR: Synesthesia is the fusion of any two perceptions elicited by a single stimulus. A good example is grapheme-color synesthesia where reading a word causes you to see that word in a particular color. In this article, I discuss the different types of synesthesia, the origins of synesthesia, the neurological cause of synesthesia, who in our history has had it, and how it might be possible for someone without synesthesia to induce it in themselves; meaning that you, the reader, could start seeing black and white words in color if you wish. And to help the reader try and elicit synesthesia, I built a google chrome extension (that’s still in the beta-phase) that can color words on webpages.
Perception is the way humans process external stimulus. But to understand the nature of perception consider the classic example of defining color. Imagine Sam and Bob are asked what color this strawberry is.
Both Sam and Bob say that the strawberry is red.
Then they’re asked to describe the color to a blind man. This gives them pause but ultimately they come to the conclusion that red is 440 nm of light.
But finally they’re asked to describe to the man how they personally interpret red. This is no longer a question about what color the strawberry is but more so a question of what the color red appears to be for Sam and for Bob respectively.
This question is very difficult to answer because there is no way to compare what Sam sees in his mind to what Bob sees in his (for now). For all we know, Sam’s perception of green may be equivalent to Bob’s perception of red. But they don’t know that since Sam’s always associated his perception of red to 440nm and Bob’s always associated his perception of red to 440nm.⁰
The nature of perception is intimately intertwined with the person observing the external stimulus. In humans, perception doesn’t always manifest itself as the interpretation of our physical senses — like seeing 440 nm wavelength of light as red. In fact, concepts like physics, biology, chemistry, psychology, time, language are all aspects of reality that we must interpret through the complex medium that is our brain. By interpreting these concepts through our brain, they become simplifications of reality —our minds grasp the overall message but perhaps not all the details.
Yet there are still measurable differences in perceptions which can be both classified and defined. Seeing something that isn’t there is considered a hallucination. Prosopagnosia is the inability to perceive faces. Akinetopsia is motion blindness or an inability to perceive fluid movements. Achromatopsia is color blindness — an inability to perceive color.
Our brain can have a lot of “glitches”. But alterations to perception are not always bad. In fact, I’d like to focus on one that’s rather extraordinary: synesthesia.
By definition, synesthesia is an automatic, consistent perceptual reaction to stimulus that doesn’t corrupt true observations of the world (called veridical perception).
Take an extreme example: Imagine for a moment that your dog is running at you. And as he walks, Bach’s Cello Suite plays in the background, each one of his legs a baton to an invisible orchestra in your head. And each time your dog pauses the cello suite pauses; sometimes it restarts, other times the concert marches on.
This is an example of hearing motion synesthesia. Every time a dog moves, Bach conducts (if you want to see if you have sound synesthesia induced by movement check out this video). But notice that the true nature of reality — the dog walking — is unperturbed, which is different than a hallucination; someone hallucinating doesn’t see the true nature of reality, while someone with synesthesia does see the true nature of reality and something more.
Typically, different synesthesias are defined by their inducers and their concurrents. An inducer is some sort of observation that a person makes. The concurrent is the perception that isn’t normally there. So in the dog example, the inducer would be the movement of the dog and the concurrent would be the perceived sounds heard.
These pairings are typically unidirectional, meaning that if a person heard music and saw colors then that person may not necessarily see colors and hear music. Examples of different synesthesias and their inducer → concurrent pairings are listed below.
Examples of Types of Synesthesia
- Grapheme-Color Synesthesia: (character → color). Seeing a character highlighted in a particular color
- Mirror Touch Synesthesia: (seeing touch → feeling touch). Observing physical touch elicits the feeling of the observed touch without actually being touched.
- Chromesthesia: (sound → color). Sounds elicit color.
- Spatial form(numbers → space) Visualizing numbers or ordinal objects in physical space.
- Lexical-Gustatory Synesthesia: (word or phoneme → taste) Hearing a certain word or reading a word elicits tastes.
- personification synesthesia: (object → perceiving like a person) giving real personality to objects or concepts.
If you want to see what it’s like to have chromesthesia — hear colors — check out the beautiful example below.
Wouldn’t it be fantastic if we could induce synesthesia in ourselves? To see words constantly in color, to see a light-show with notes? Not only does this seem to boost creativity but there are cognitive advantages that come with synesthesia as well. Additionally, some of the greatest minds in history have had synesthesia. (…read on to learn more.)
The examples above are a few of the many different kinds of synesthesia. The interesting part about synesthesia is that it is a fusion of different perceptions. The inducer elicits the typical perception as well as the concurrent. The concurrent doesn’t alter the typical perception.
In an effort to understand how everyone can elicit synesthesia, let’s start with where synesthesia comes from. Why do people develop synesthesia? What predisposes them to synesthesia? Fair warning, I’ll be discussing quite a bit about the current literature on synesthesia as well as relevant aspects of the mind in an effort to help you, the reader, understand both why inducing synesthesia is possible and how to do it.
Why People have Synesthesia (Origins of Synesthesia)
One hypothesis is that synesthesia is caused by currently unknown genetic dispositions. Roughly 40% of synesthetes report a first-degree relative who also has synesthesia, suggesting some sort of polygenetic inheritance. For a while it was thought that synesthesia was X-linked since studies found more female synesthetes to male synesthetes ratio, however this hypothesis has largely been disproved since the disproportionate amount of females seems to be due to methodological flaws [23]
Another factor that could cause synesthesia to develop is brain injury. In order to understand how brain injuries can cause synesthesia we need to digress and learn about the modality of the cerebral cortex, goal-oriented behavior, and how selective attention works in order to understand how sensitive the brain is to perturbations.
There are both structural and functional divisions of the brain¹. Structural divisions highlight human evolution and can be thought of in a hierarchy that varies in complexity. Brains have a brain stem controlling important homeostasis functions, a limbic system playing a role in emotions (and more) and finally surrounding the limbic system is the cerebral cortex which is responsible for most of our complex behavior (abstract thought, speech to name a few). See the image to the left for a visual³. Functional divisions however are regions of the brain that can seem to operate together for a particular task. I’ll be focusing on the functional divisions of the cerebral cortex for now.
The image to the left illustrates how different regions of the cortex are used for different functions. The somatosensory cortex gives us the sensation of touch, the visual cortex processes visual input, the auditory cortex processes the sounds we hear, etc. Most of the time, these regions only get input from the stimulus sensing organs associated with their function: our eyes go to the visual cortex, our ears to the auditory cortex, our tongue the gustatory cortex, etc. and these stimuli are then transduced — or converted — into neuronal activations that our brain can interpret. While this is a simplification of the cerebral cortex and sensory transduction through the central nervous system let’s go along with this idea for now.
The next part we need to understand is goal-oriented behavior. Humans — and primates too — have evolved to have behavior that accomplishes some goal or task. While the brain does have multiple functional areas that each have their own functional role, the brain also has a leader of sorts who gathers and orchestrates these different functional regions depending on the task at hand.
This region is called the anterior cingulate cortex(ACC) and it’s found in the medial frontal cortex. Essentially, the ACC determines which areas of the brain to use for a specific task. A bit more technically, the ACC seems responsible for task-specific activation and inhibition of functional regions during goal-oriented behavior. So for example, if someone was walking in the woods and all of a sudden they stumbled onto a lion, that itch on the back of his or her calf may not be as important as deciding where the lion is in space. Hence, when the current goal becomes “get away from the lion that’s looking at me like it’s lunch time” an inhibition of the “feeling” region of the brain, the somatosensory cortex, occurs and activation of the visual cortex occurs in response to this new goal.
Goal oriented behavior is intertwined with attentional control also called selective attention. Evidence suggests that the areas represented in the image to the left — the dorsal field and the ventral field — are essential for selective attention. Damage in these areas can cause inabilities to attune to particular senses, such as the entire right hand side of space in what’s called spacial neglect.
Now, that was a lot, but let’s take a step back for a moment. Why did I describe different functional regions of the cerebral cortex, goal-oriented behavior, and attention to begin with? The main purpose was to highlight how intricate the communication within the brain can become when trying to accomplish a specific goal. The other reason was to emphasize how delicate this system can be. A brain injury can potentially disrupt certain pathways and systems and cause regions that weren’t originally communicating to start talking to one another. So, returning to the lion example, imagine that the person had an injury that resulted in a disinhibition of the gustatory pathway during attention. Now when the person sees the lion he or she sees both the lion and tastes honey?
Another hypothesis for why synesthesia occurs after brain injury is that because of the brain’s neural plasticity there is proliferation of neural pathways creating connections between different functional areas that didn’t exist before. So now, two adjacent functional areas — like the area that processes visual word input and color — may become connected, which in this example could lead to grapheme-color (word induces color) synesthesia in the person who suffered a brain injury.²
Another theory for the origin of synesthesia is that it could confer an advantage in learning for younger children. During the critical period of childhood (good overview of the critical period can be found here), a child’s perception of two concepts become connected somehow through associative learning. In which case, this new fusion of perception helps the child understand new information about these learned concepts. For instance, if a child is having trouble playing the piano perhaps seeing the notes in color helps the child understand why the notes were out of tune. So, overtime, the child’s brain strengthens the pathway that pairs the auditory cortex with the visual cortex giving the child the ability to see colored notes. In fact, the majority of inducers for people with synesthesia are concepts that are tricky for children to learn; graphemes, time, and music to name a few. So, children with synesthesia might use their synesthetic perception of the concurrent to better understand the inducer [6,24,26]
While genetic dispositions, brain injury, and childhood development seem to increase the likelihood of someone developing synesthesia, what are the similarities within the brain that underly synesthesia, if any? Is there possibly an easy way to elicit synesthesia in people who don’t have it by modifying something in the brain?
A bit more technically, what and where are the structural or functional differences of the brains of syntesthetes compared to nonsynesthetic controls?
The neurological underpinnings of synesthesia
Basically, it seems that synesthesia occurs when different regions of the brain light up together at the same time. A bit more technically, there’s evidence that synesthesia is caused by simultaneous activation of different functional regions of the brain but the underlying mechanism causing the simultaneous activation is still being debated. One hypothesis is that hyperconnectivity is due to increased white matter tracts between functional regions[20], however there are some articles that argue there is no change in the structure of the brain [19]. Some articles notice larger gray matter volumes in functional regions that perceive the inducer stimulus [21]. Others notice changes in both grey matter and white matter[22]. It’s possible that because there are multiple modalities of communication in the brain such white matter, grey matter, glial cells, etc. , and intricate methods of communicating such as goal-oriented communication, speech related connections, etc., influencing or modifying only one of these modalities or parts of the communication network pathways can result in synesthesia. However, more research needs to be done.
I also wanted to detail briefly how I analyze the articles I read. The main idea of the following two summaries is to illustrate how to extract the main argument from an article and understand whether or not the methods used by the article are sufficient to support that main argument. If you’re interested go ahead and keep reading, otherwise skip to the “Why Synesthesia is Worth Investigating” section.
Article Summaries
The following articles are ones that support the idea that synesthesia is caused by hyperconnectivity in the brain. One of the main limitations I’d like to highlight to the reader is that the number of synesthete in both experiments is small.
Intrinsic Network Connectivity Reflects Consistency of Synesthetic Experiences (Dovern et al.): The main idea: In this article, neuroscientists used fMRI technology (learn more about fMRIs here) as a measurement for connectivity in the brains of grapheme-synesthetes. They primarily noted more connectivity between the right frontoparietal region and the visual cortex(see images below).
A functional connectivity difference was found using fMRI voxel based analysis. The fMRI voxel BOLD activation time series was then used in independent component analysis (ICA). ICA generated different interconnected regions that could then be analyzed as their own connected network; the hope of ICA is to discover highly connected regions that are used for specific functions, i.e the visual cortex would be considered its own connected region. The results found higher activity in the areas connecting the medial and lateral visual areas to the fronto-parietal area of synesthetes compared to controls. [14]. I would also say based on other literature I’ve read that the left fronto-parietal lobe is also active in grapheme-color synesthetes, but in this study the differences in ICN activity seems not to have been significant.
Multiple neural mechanisms for coloring words in synesthesia: the main idea: The main experiment used MEG imagining to measure visually evoked fields (VEFs)on the brain. By comparing two grapheme-synesthetes VEF differences to control VEF differences researchers found that there was more activation in specific regions of the visual cortex of synesthetes compared to controls which may explain the underlying synesthete experience for specific characters. Additionally, the perception of seeing a word in color was associated with more activation of the left inferior cortex of syntesthetes compared to controls that occurred with activation of the visual cortex. The sample size of this experiment was 2 syntesthetes and 11 controls (small).
The main methods of this experience come from the following table
The synesthetes had a particular form of synesthesia where for some words they were able to experience complete coloring based on that word, such as POST being seen entirely as red, while for other words coloring only depended on the first character the syntesthetes read, such as RICE where the word itself didn’t evoke a specific color but rather the color paired with R did.
All subjects were then prompted with tests that contained a word or a series of characters that obeyed one of the following specific rules:
- The semantic rule was simply a word that became completely colored when the synesthete saw that word, and pseudo semantic was that same word rearranged (POST became TOSP) causing the synesthete to perceive a word in a specific color according only to the first character and not the entire word.
- The first letter (lexical synesthesia), greek rule was trying to measure how brain activity changed when a synesthete recognized the characters and thus perceived the series of characters in a different colors vs didn’t recognize the characters and had no perception change; this was done by prompting the subjects with a series of english characters and also a series of greek characters and measuring the difference in brain activity.
- The semantic rule experiment
Part B of the graphs indicate the semantic and first letter VEFs of the two synesthetes M.S and T.H and the controls.
Part C represents the differences in semantic and first letter VEFs of all groups; the observation being that both syntesthetes had more activation (as VEFs) in the frontal temporal lobe than the controls when prompted with words that evoked their own color compared to words that were colored only based on the first character.
2. The first letter, greek rule experiment
The differences in the greek and pseudo semantic VEFs for each group are illustrated in part C and may illustrate which regions are activated when triggered by a specific character. It seems that with the controls any character, english or greek, activates only one region of the visual cortex while for the synesthetes english characters in particular elicit higher activation in both the “character processing region” in V4 and posterior temporal grapheme areas in the visual cortex. These results suggest that unlike semantic induced color synesthesia where the fronto-parietal cortex is activated, character based synesthesia activates the aforementioned regions in the visual cortex.
Why Synesthesia is Worth Investigating
But why is synesthesia interesting? Synesthesia isn’t normally a dysfunction (in some cases it can be for example with misophonia where the inducer is paired with a negative emotion) so why is it worth studying? For one, synesthesia can result in boosts in cognitive tasks, such as memory recall, verbal working memory, and visuospatial processing and reasoning in synesthesia related tasks. For example, people with grapheme-color synesthesia had better recall of visual tests, and people with sound synesthesia had a better recall of auditory tests [4]. Synesthesia has the potential to help with cognitive tasks that come from processing the inducer stimulus; for example, a grapheme-color synesthesia who reads a shopping list may recall everything on the list because of the colors it elicited. [4] What’s also interesting is that people with synesthesia have showed slower mental decline while aging compared to controls [13].
Another interesting reason is that these sort of cognitive gains have existed in some of the most extraordinary and intelligent individuals in history.
The following paragraph discusses different synesthetes as well as their respective types of synesthesia.
- Kaitlyn Hova: chromesthesia
- Richard Feynman: Grapheme-Color synesthesia
- Daniel Tammet: sort of spatial form, grapheme-color, chromesthesia blend. His synesthesia is rather unique.
- Nikola Tesla: auditory → visual, his synesthesia is also unique
- Vladimir Nabokov: Grapheme-Color synesthesia
- Hans Zimmer: chromesthesia
- Leigh Erceg: chromesthesia, grapheme-color synesthesia, spatial form.
- Acquired Synesthesia: Jason Padgett: visual → geometric shapes, his synesthesia is also unique.
- Aquired Synesthesia: Neil Harbin: visual → music tones, his synesthesia is more in the realm of cybernetics and human bioengineering.
People who had synesthesia
Kaitlyn Hova is the musician and synestheste in the virtual reality video above and she has chromesthesia. For more details see the VR video above;
Richard Feynman, one of my role models, was a synesthete. According to his book What Do You Care What Other People Think he reveals that he was a graphene-synesthete: he associated numbers and letters (which acted as numeric symbols) with particular colors. Sometimes when “[he]sees equations, [he] sees the letters in colors”[30].
Another example is the savant Daniel Tammet. Savant syndrome is when someone has remarkable capabilities in one particular area, usually despite some mental condition. In Daniel’s case, he was diagnosed with Aspergers and as an autistic (Aspergers) savant. Daniel blends numbers, shapes, and words into personified visual imagery that’s blended with color.
According to a documentary on his life (link here) he doesn’t see numbers but experiences numbers as different colors, shapes, textures, and even movements forming visual landscapes in his mind. In the documentary he describes 1 as a bright light that’s like a flashlight in his face. 2 is a movement from right to left. 5 is the clap of thunder or the sound of a wave against a rock. 6 is small and is the absence of something. 9 is a large number and can be intimidating. So for him, numbers create visual shows and personable actions that becomes the landscape he sees in his mind. [1, 15]
Another example is Nikolas Tesla. Nikolas Tesla had visual synesthesia induced by spoken word.
“When a word was spoken, the image of the object would present itself so vividly to [his] vision, that [he]could not tell whether what [he] saw was real or not… Even though [he] reached out and passed [his] hand through it, the image would remain fixed in space.” [5]. His synesthesia allowed him to visualize the majority of his inventions and design them in his mind, before he wrote anything down. Hence the reason why a majority of his designs were left with characteristically few details.[2]
Vladimir Nabokov, a Russian novelist most famous for his long prose in works like Lolita, sees letters in different colors and sometimes associated different sounds of a letter with different color another example of grapheme-color synesthesia. For example,“The long “a” of the English alphabet has for me the tint of weathered wood, but a French “a” evokes polished ebony” (an interview with BBC 1962). Also Nab(1899–1977) described the letters kzspygv as creating the spectrum from red to violet. [4, 31]
Hans Zimmer, a famous composer who created the soundtrack behind Pirates of the Caribbean, The Dark Night, Superman and more, also has chromesthesia
People who acquired synesthesia
Like we discussed, some synesthetes have have had with their abilities for as long as they remember, but there are others who acquired their abilities after a brain injury.
Jason Padgett is a case of acquired synesthesia. Due to a brain injury he suffered when he was mugged, Jason began seeing fractals everywhere in the world around him. According to an interview, he sees everything in discrete time chunks with fractals persisting over the natural geometry of the world.
Leig Erceg also acquired a rather unique synesthesia after falling into a ravine (source). She apparently attunes to details of an observation first before seeing the overall message of the observation first. She also has grapheme-synesthesia and chromesthesia because of here accident and is now an extraordinarily gifted artist — both in her drawings and her poetry. [18]
Another interesting case of synesthesia is Neil Harbisson. His synesthesia was more so created than acquired. Neil has complete color blindness. So, in an effort to perceive color, he attached what he calls a cyborg antenna to his occipital bone that vibrates at different frequencies of light, allowing him to perceive color as sounds. So his synesthesia is an interesting blend of visual input with different sounds that vary depending on the color.
And the above is only a small subset of the actual population of people who have synesthesia. While there doesn’t seem to be an agreed upon percentage of the population, there are still potentially millions of people across the globe with synesthesia — all with possibly unique synesthesia perceptions.
And what’s amazing is that it’s possible for people without synesthesia to induce it in themselves. There are experiments where scientists attempt to elicit synesthesia in people who don’t have it, and what’s more is that in some they succeeded.
How to Induce Synesthesia
In Acquiring Synaesthesia: Insights from Training Studies by Rothen and Meier they reference a study where researchers attempted to associate tones to color, in particular the tones C and G to red and green. What they found is that after a sufficient number of trials participants began hearing C and seeing red and hearing G and seeing green! An automatic, consistent association occurred[27]. So yes, it is possible to induce synesthesia.
Another study used trained patients to specific grapheme-color where particular characters in the alphabet were mapped to a particular color (a to red, b to blue, c to green …). After approximately four weeks, participants showed a significant stroop effect and interestingly they made internal associations with the character and the color. However, participants did not have the typical synesthesia perceptual visual experience of the color when seeing the character. And, when participants were asked to undergo an identification task searching for a particular character, they fared as well as controls, highlighting the fact that there was no perceptual experience [27]. One possible reason for this could be methodology issues in duration of reading colored words or perhaps the length of the actual experiment.
Other types of learning vectors (such as associative and supervised) were used to try and pair inducers to concurrents however it seems that perceptual experience is usually what’s absent after training [27]. Yet, I’d guess that perhaps there is some issue in the experimental setup since there are experiments where synesthesia has been successfully induced; maybe time and the subject’s effort during experimental training.
There are still studies though that show that after sufficient training patients can start experiencing colors when seeing certain letters. There have been people in a colored novel-reading study that reported that they began experiencing colors when thinking about certain letters [26].
But the main reason why I hypothesize that synesthesia can be induced is because there are methods that can alter the functional connectivity of the brain like meditation. In one study by Hernández, Sergio Elías, et al. [28], they noticed increased gray matter volume in the ACC and the insula in people who meditated with the goal of achieving mental silence. Note that the insula can be thought of as a crossroads that interconnects many different regions of the brain: the limbic system (plays a role in emotion), sensory regions of the cortex like the visual cortex, even the reward based pathways [29]. As mentioned earlier in this article, the ACC plays a role in goal-oriented behavior and attention, so if functional connectivity changes with prolonged focus on a goal then perhaps if the goal changed to become visualizing the colors that were paired to particular words during synesthesia based training there would be a different kind of functional connectivity change that would overtime develop into the functional connectivity associated with synesthetes.
A possibly interesting experiment
One experiment for the future might be to train patients on character → color pairs and have then have them meditate on the characters and their associated colors, attempting to used mediation to elicit the colors. I’ve reached out to leading synesthesia researchers in the field to see if this hypothesis seems plausible (no response yet)⁴.
But until then, I leave this up to the reader to try and induce synesthesia in themselves. I have built a google chrome extension (firefox coming soon) that changes the words on webpages into specific colors. How to use the chrome extension is listed here. The hope is that someone wishing to induce synesthesia uses the chrome extension to train on colored words while also taking periodic times during their day to mediate on some of these colored words⁵; like visualizing apple as red for example.
Synesthesia is a beautiful phenomenon and my hope is that by understanding the condition we might be able to give all people the option to have it themselves. So if you’re interested in inducing grapheme-color, try my extension. Or even try making up your own experiment to elicit different synesthesias like chromesthesia, or personification. You might just find that your world is a bit more colorful, louder, and crowded.
Special thanks to my brother Lazare for helping me organize and review this article. Couldn’t have done it without you.
Footnotes
0. Some argue that we can measure perception by analyzing the network formed by neurons in our brain. Thus, the argument is that if two people, Sam and Bob, seeing the color red have the exact same neural pathway that fires in the exact same manner then their perceptions are identical. One good video illustrating this argument can be found here. However, one problem with this argument is that even if the two pathways are logically the identical, the two pathways are still physically different (if you’re interested in the difference between logical and physical equivalence look at my other article here). So the only way to be certain that the perceptions are the same is to take neural pathway found in Sam’s head and transplant it somehow into Bob’s mind and then show Bob 440nm of light and ask “what color do you see”. If he sees red then only then will their perceptions be equivalent.
1. There’s also pedagogical divisions making it easier to analyze certain regions like Brodmanns areas.
2. While this may be obvious to some I would like to emphasize that brain injuries typically do not result in beneficial abilities and most of the time these injuries come at a terrible cost such as depression, constant migraines, and loss of function in some other area that varies on a case by case basis. Please do not use this article to support the conclusion that getting brain injuries is good; it’s not. Be safe and wear a helmet.
3. Another image representing the structural hierarchy of the brain and it’s plasticity (Bruce Duncan Perry)
4. If I had the resources, I’d like to conduct an experiment that compares the brain activation across three groups: syntesthetes, nonsynesthetes trying to elicit synesthesia with meditation based training, and nonsynesthetetic controls. I hypothesize that overtime nonsynesthetes using meditation to elicit grapheme-color synesthesia would overtime show increasing similarity of functional connectivity of regions in the brain (fronto-parietal lobe connected to visual cortex) that match the functional connectivity of grapheme-color synesthetes compared to the controls.
5. If you’re interested, I highlight my original goals for the project here
References
- (savants that has daniel tammet in it) https://www.youtube.com/watch?v=PPySn3slfXI
- https://futurism.com/know-your-scientist-nikola-tesla
- https://www.firstshowing.net/2013/interview-man-of-steel-composer-hans-zimmer/
- New insights into mechanisms of enhanced synaesthetic memory: Benefits are synaesthesia-type-specific by Lunke, Katrin
Meier, Beat - Futurism, from 1921 interview for the American Magazine
- Ward, Jamie. “Synesthesia.” Annual Review of Psychology, vol. 64, no. 1, Feb. 2013, p. 49. EBSCOhost, libproxy.berkeley.edu/login?qurl=http%3a%2f%2fsearch.ebscohost.com%2flogin.aspx%3fdirect%3dtrue%26db%3dedb%26AN%3d84578718%26site%3deds-live.
- Arend, Isabel, et al. “Neuroanatomical Basis of Number Synaesthesias: A Voxel-Based Morphometry Study.” CORTEX, vol. 101, pp. 172–180. EBSCOhost, doi:10.1016/j.cortex.2018.01.020. Accessed 12 Nov. 2018.
- (neuroanotamtomical evidence for differences in GM b/w synesthestes with different inducer-component pairings)
- Meier, Beat and Nicolas Rothen. “Developing synaesthesia: a primer” Frontiers in human neuroscience vol. 9 211. 20 Apr. 2015, doi:10.3389/fnhum.2015.00211
- Rothen N and Meier B (2014) Acquiring synaesthesia: insights from training studies. Front. Hum. Neurosci. 8:109. doi: 10.3389/fnhum.2014.00109
- Lindahl, Jared R et al. “A phenomenology of meditation-induced light experiences: traditional buddhist and neurobiological perspectives” Frontiers in psychology vol. 4 973. 3 Jan. 2014, doi:10.3389/fpsyg.2013.00973
- Jared Medina, Carrie DePasquale et al.“influence of the body schema on mirror-touch”. Science Direct.
- https://www.theguardian.com/science/2014/apr/27/benefit-synaesthesia-brain-injury-mental-decline
- http://www.jneurosci.org/content/32/22/7614/tab-figures-data
- https://www.psychologytoday.com/us/blog/feeling-too-much/201408/daniel-tammet-autistic-and-synesthetic-savant
- Investigate article: Multiple neural mechanisms for coloring words in synesthesia https://www.ncbi.nlm.nih.gov/pubmed/24486829
- Explanation of what MEG is (http://web.mit.edu/kitmitmeg/whatis.html)
- https://abcnews.go.com/Health/colorado-rancher-suffers-traumatic-brain-injury-accidental-genius/story?id=31053667
- Dojat, Michel, et al. “Magnetic Resonance Imaging Does Not Reveal Structural Alterations in the Brain of Grapheme-Color Synesthetes.” PLoS ONE, vol. 13, no. 4, Apr. 2018, pp. 1–21. EBSCOhost, doi:10.1371/journal.pone.0194422.
- Whitaker, Kirstie J., et al. “White Matter Microstructure throughout the Brain Correlates with Visual Imagery in Grapheme–color Synesthesia.” NeuroImage, vol. 90, Apr. 2014, pp. 52–59. EBSCOhost, doi:10.1016/j.neuroimage.2013.12.054.
- Arend, Isabel, et al. “Research Report: Neuroanatomical Basis of Number Synaesthesias: A Voxel-Based Morphometry Study.” Cortex, vol. 101, Apr. 2018, pp. 172–180. EBSCOhost, doi:10.1016/j.cortex.2018.01.020.
- Hänggi, Jürgen, et al. “The Multiple Synaesthete E.S. — Neuroanatomical Basis of Interval-Taste and Tone-Colour Synaesthesia.” Neuroimage, vol. 43, Jan. 2008, pp. 192–203. EBSCOhost, doi:10.1016/j.neuroimage.2008.07.018.
- Brang, David and V S Ramachandran. “Survival of the synesthesia gene: why do people hear colors and taste words?” PLoS biology vol. 9,11 (2011): e1001205.
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